Hubbry Logo
Functional groupFunctional groupMain
Open search
Functional group
Community hub
Functional group
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Contribute something
Functional group
Functional group
Functional group
View on Wikipedia
from Wikipedia
Example functional groups of benzyl acetate:
  Ester group
  Acetyl group
  Benzyloxy group

In organic chemistry, a functional group is any substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition.[1][2] This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis.

A functional group is a group of atoms in a molecule with distinctive chemical properties, regardless of the other atoms in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule by covalent bonds. For repeating units of polymers, functional groups attach to their nonpolar core of carbon atoms and thus add chemical character to carbon chains. Functional groups can also be charged, e.g. in carboxylate salts (−COO−), which turns the molecule into a polyatomic ion or a complex ion. Functional groups binding to a central atom in a coordination complex are called ligands. Complexation and solvation are also caused by specific interactions of functional groups. In the common rule of thumb "like dissolves like", it is the shared or mutually well-interacting functional groups which give rise to solubility. For example, sugar dissolves in water because both share the hydroxyl functional group (−OH) and hydroxyls interact strongly with each other. Plus, when functional groups are more electronegative than atoms they attach to, the functional groups will become polar, and the otherwise nonpolar molecules containing these functional groups become polar and so become soluble in some aqueous environment.

Combining the names of functional groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, the first carbon atom after the carbon that attaches to the functional group is called the alpha carbon; the second, beta carbon, the third, gamma carbon, etc. If there is another functional group at a carbon, it may be named with the Greek letter, e.g., the gamma-amine in gamma-aminobutyric acid is on the third carbon of the carbon chain attached to the carboxylic acid group. IUPAC conventions call for numeric labeling of the position, e.g. 4-aminobutanoic acid. In traditional names various qualifiers are used to label isomers, for example, isopropanol (IUPAC name: propan-2-ol) is an isomer of n-propanol (propan-1-ol). The term moiety has some overlap with the term "functional group". However, a moiety is an entire "half" of a molecule, which can be not only a single functional group, but also a larger unit consisting of multiple functional groups. For example, an "aryl moiety" may be any group containing an aromatic ring, regardless of how many functional groups the said aryl has.

Table of common functional groups

[edit]

The following is a list of common functional groups.[3] In the formulas, the symbols R and R' usually denote an attached hydrogen, or a hydrocarbon side chain of any length, but may sometimes refer to any group of atoms.

Hydrocarbons

[edit]

Hydrocarbons are a class of molecule that is defined by functional groups called hydrocarbyls that contain only carbon and hydrogen, but vary in the number and order of double bonds. Each one differs in type (and scope) of reactivity.

Chemical class Group Formula Structural Formula Prefix Suffix Example
Alkane Alkyl R(CH2)nH Alkyl alkyl- -ane
Ethane
Alkene Alkenyl R2C=CR2 Alkene alkenyl- -ene ethylene
Ethylene
(Ethene)
Alkyne Alkynyl RC≡CR′ alkynyl- -yne
Acetylene
(Ethyne)
Benzene derivative Phenyl RC6H5
RPh 		Phenyl phenyl- -benzene
Cumene
(Isopropylbenzene)

There are also a large number of branched or ring alkanes that have specific names, e.g., tert-butyl, bornyl, cyclohexyl, etc. There are several functional groups that contain an alkene such as vinyl group, allyl group, or acrylic group. Hydrocarbons may form charged structures: positively charged carbocations or negative carbanions. Carbocations are often named -um. Examples are tropylium and triphenylmethyl cations and the cyclopentadienyl anion.

Groups containing halogens

[edit]

Haloalkanes are a class of molecule that is defined by a carbon–halogen bond. This bond can be relatively weak (in the case of an iodoalkane) or quite stable (as in the case of a fluoroalkane). In general, with the exception of fluorinated compounds, haloalkanes readily undergo nucleophilic substitution reactions or elimination reactions. The substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity.

Chemical class Group Formula Structural formula Prefix Suffix Example
haloalkane halo RX halo- alkyl halide
Chloroethane
(Ethyl chloride)
fluoroalkane fluoro RF fluoro- alkyl fluoride
Fluoromethane
(Methyl fluoride)
chloroalkane chloro RCl chloro- alkyl chloride Chloromethane
Chloromethane
(Methyl chloride)
bromoalkane bromo RBr bromo- alkyl bromide
Bromomethane
(Methyl bromide)
iodoalkane iodo RI iodo- alkyl iodide Iodomethane
Iodomethane
(Methyl iodide)

Groups containing oxygen

[edit]

Compounds that contain C–O bonds each possess differing reactivity based upon the location and hybridization of the C–O bond, owing to the electron-withdrawing effect of sp-hybridized oxygen (carbonyl groups) and the donating effects of sp2-hybridized oxygen (alcohol groups).

Chemical class Group Formula Structural formula Prefix Suffix Example
Alcohol Hydroxy ROH
Hydroxyl
Hydroxyl
 hydroxy- -ol methanol
Methanol
Ketone Ketone RCOR′ Ketone -oyl- (-COR′)
or
oxo- (=O)		 -one Butanone
Butanone
(Methyl ethyl ketone)
Aldehyde Aldehyde RCHO Aldehyde formyl- (-COH)
or
oxo- (=O)		 -al acetaldehyde
Acetaldehyde
(Ethanal)
Acyl halide Haloformyl RCOX Acyl halide carbonofluoridoyl-
carbonochloridoyl-
carbonobromidoyl-
carbonoiodidoyl-		 -oyl fluoride
-oyl chloride
-oyl bromide
-oyl iodide 		Acetyl chloride
Acetyl chloride
(Ethanoyl chloride)
Carbonate Carbonate ester ROCOOR′ Carbonate (alkoxycarbonyl)oxy- alkyl carbonate triphosgene
Triphosgene
(bis(trichloromethyl) carbonate)
Carboxylate Carboxylate RCOO−
Carboxylate
Carboxylate

Carboxylate 		carboxylato- -oate Sodium acetate
Sodium acetate
(Sodium ethanoate)
Carboxylic acid Carboxyl RCOOH Carboxylic acid carboxy- -oic acid Acetic acid
Acetic acid
(Ethanoic acid)
Ester Carboalkoxy RCOOR′ Ester alkanoyloxy-
or
alkoxycarbonyl 		alkyl alkanoate Ethyl butyrate
Ethyl butyrate
(Ethyl butanoate)
Hydroperoxide Hydroperoxy ROOH Hydroperoxy hydroperoxy- alkyl hydroperoxide tert-Butyl hydroperoxide
tert-Butyl hydroperoxide
Peroxide Peroxy ROOR′ Peroxy peroxy- alkyl peroxide Di-tert-butyl peroxide
Di-tert-butyl peroxide
Ether Ether ROR′
Ether
Ether
 alkoxy- alkyl ether Diethyl ether
Diethyl ether
(Ethoxyethane)
Hemiacetal Hemiacetal R2CH(OR1)(OH) Hemiacetal alkoxy -ol -al alkyl hemiacetal
Hemiketal Hemiketal RC(ORʺ)(OH)R′ Hemiketal alkoxy -ol -one alkyl hemiketal
Acetal Acetal RCH(OR′)(OR″) Acetal dialkoxy- -al dialkyl acetal
Ketal (or Acetal) Ketal (or Acetal) RC(OR″)(OR‴)R′ Ketal dialkoxy- -one dialkyl ketal
Orthoester Orthoester RC(OR′)(OR″)(OR‴) Orthoester trialkoxy-
Heterocycle
(if cyclic)		 Methylenedioxy (–OCH2O–)

methylenedioxy- -dioxole
1,2-Methylenedioxybenzene
(1,3-Benzodioxole)
Orthocarbonate ester Orthocarbonate ester C(OR)(OR′)(OR″)(OR‴) Orthocarbonate ester tetralkoxy- tetraalkyl orthocarbonate
Tetramethoxymethane
Organic acid anhydride Carboxylic anhydride R1(CO)O(CO)R2 Carboxylic anhydride anhydride Butyric anhydride
Butyric anhydride

Groups containing nitrogen

[edit]

Compounds that contain nitrogen in this category may contain C-O bonds, such as in the case of amides.

Chemical class Group Formula Structural formula Prefix Suffix Example
Amide Carboxamide RCONR'R" Amide carboxamido-
or
carbamoyl-		 -amide acetamide
Acetamide
(Ethanamide)
Amidine Amidine R4C(NR1)(NR2R3) amidino- -amidine acetamidine

(acetimidamide)

Guanidine Guanidine RNC(NR2)2) Guanidin- -Guanidine
Guanidinopropionic acid
Amines Primary amine RNH2 Primary amine amino- -amine methylamine
Methylamine
(Methanamine)
Secondary amine R'R"NH Secondary amine amino- -amine dimethylamine
Dimethylamine
Tertiary amine R3N Tertiary amine amino- -amine trimethylamine
Trimethylamine
4° ammonium ion R4N+ Quaternary ammonium cation ammonio- -ammonium Choline
Choline
Hydrazone R'R"CN2H2 hydrazino- -hydrazine
Benzophenone
Imine Primary ketimine RC(=NH)R' Imine imino- -imine
Secondary ketimine RC(=NR)R' Imine imino- -imine
Primary aldimine RC(=NH)H Imine imino- -imine Ethanimine
Ethanimine
Secondary aldimine RC(=NR')H Imine imino- -imine
Imide Imide (RCO)2NR' Imide imido- -imide Succinimide
Succinimide
(Pyrrolidine-2,5-dione)
Azide Azide RN3 Organoazide azido- alkyl azide Phenyl azide
Phenyl azide
(Azidobenzene)
Azo compound Azo
(Diimide) 		RN2R' Azo.pngl azo- -diazene Methyl orange
Methyl orange
(p-dimethylamino-azobenzenesulfonic acid)
Cyanates Cyanate ROCN Cyanate cyanato- alkyl cyanate Methyl cyanate
Methyl cyanate
Isocyanate RNCO Isocyanate isocyanato- alkyl isocyanate Methyl isocyanate
Methyl isocyanate
Nitrate Nitrate RONO2 Nitrate nitrooxy-, nitroxy-

alkyl nitrate

Amyl nitrate
Amyl nitrate
(1-nitrooxypentane)
Nitrile Nitrile RCN cyano- alkanenitrile
alkyl cyanide 		Benzonitrile
Benzonitrile
(Phenyl cyanide)
Isonitrile RNC isocyano- alkaneisonitrile
alkyl isocyanide
Methyl isocyanide
Nitrite Nitrosooxy RONO Nitrite nitrosooxy-

alkyl nitrite

Amyl nitrite
Isoamyl nitrite
(3-methyl-1-nitrosooxybutane)
Nitro compound Nitro RNO2 Nitro nitro-   Nitromethane
Nitromethane
Nitroso compound Nitroso RNO Nitroso nitroso- (Nitrosyl-)   Nitrosobenzene
Nitrosobenzene
Oxime Oxime RCH=NOH Oxime   Oxime Acetone oxime
Acetone oxime
(2-Propanone oxime)
Pyridine derivative Pyridyl RC5H4N

4-pyridyl group
3-pyridyl group
2-pyridyl group

4-pyridyl
(pyridin-4-yl)

3-pyridyl
(pyridin-3-yl)

2-pyridyl
(pyridin-2-yl)

-pyridine Nicotine
Nicotine
Carbamate ester Carbamate RO(C=O)NR2 Carbamate (-carbamoyl)oxy- -carbamate Chlorpropham
Chlorpropham
(Isopropyl (3-chlorophenyl)carbamate)

Groups containing sulfur

[edit]

Compounds that contain sulfur exhibit unique chemistry due to sulfur's ability to form more bonds than oxygen, its lighter analogue on the periodic table. Substitutive nomenclature (marked as prefix in table) is preferred over functional class nomenclature (marked as suffix in table) for sulfides, disulfides, sulfoxides and sulfones.

Chemical class Group Formula Structural formula Prefix Suffix Example
Thiol Sulfhydryl RSH Sulfhydryl sulfanyl-
(-SH) 		-thiol Ethanethiol
Ethanethiol
Sulfide
(Thioether) 		Sulfide RSR' Sulfide group substituent sulfanyl-
(-SR') 		di(substituent) sulfide
Dimethyl sulfide

(Methylsulfanyl)methane (prefix) or
Dimethyl sulfide (suffix)
Disulfide Disulfide RSSR' Disulfide substituent disulfanyl-
(-SSR') 		di(substituent) disulfide
Dimethyl disulfide

(Methyldisulfanyl)methane (prefix) or
Dimethyl disulfide (suffix)
Sulfoxide Sulfinyl RSOR' Sulfinyl group -sulfinyl-
(-SOR') 		di(substituent) sulfoxide DMSO
(Methanesulfinyl)methane (prefix) or
Dimethyl sulfoxide (suffix)
Sulfone Sulfonyl RSO2R' Sulfonyl group -sulfonyl-
(-SO2R') 		di(substituent) sulfone Dimethyl sulfone
(Methanesulfonyl)methane (prefix) or
Dimethyl sulfone (suffix)
Sulfinic acid Sulfino RSO2H sulfino-
(-SO2H) 		-sulfinic acid Hypotaurine
2-Aminoethanesulfinic acid
Sulfonic acid Sulfo RSO3H Sulfonyl group sulfo-
(-SO3H) 		-sulfonic acid Benzenesulfonic acid
Benzenesulfonic acid
Sulfonate ester Sulfo RSO3R' Sulfonic ester (-sulfonyl)oxy-
or
alkoxysulfonyl- 		R' R-sulfonate Methyl trifluoromethanesulfonate
Methyl trifluoromethanesulfonate or
Methoxysulfonyl trifluoromethane (prefix)
Thiocyanate Thiocyanate RSCN Thiocyanate thiocyanato-
(-SCN) 		substituent thiocyanate Phenyl thiocyanate
Phenyl thiocyanate
Isothiocyanate RNCS Isothiocyanate isothiocyanato-
(-NCS) 		substituent isothiocyanate Allyl isothiocyanate
Allyl isothiocyanate
Thioketone Carbonothioyl RCSR' Thione -thioyl-
(-CSR')
or
sulfanylidene-
(=S) 		-thione Diphenylmethanethione
Diphenylmethanethione
(Thiobenzophenone)
Thial Carbonothioyl RCSH Thial methanethioyl-
(-CSH)
or
sulfanylidene-
(=S) 		-thial
Thiocarboxylic acid Carbothioic S-acid RC=OSH
Thioic S-acid
Thioic S-acid
 mercaptocarbonyl- -thioic S-acid Thiobenzoic acid
Thiobenzoic acid
(benzothioic S-acid)
Carbothioic O-acid RC=SOH
Thioic O-acid
Thioic O-acid
 hydroxy(thiocarbonyl)- -thioic O-acid
Thioester Thiolester RC=OSR' Thiolester S-alkyl-alkane-thioate S-methyl thioacrylate
S-Methyl thioacrylate
(S-Methyl prop-2-enethioate)
Thionoester RC=SOR' Thionoester O-alkyl-alkane-thioate
Dithiocarboxylic acid Carbodithioic acid RCS2H
Dithiocarboxylic acid
Dithiocarboxylic acid
 dithiocarboxy- -dithioic acid Dithiobenzoic acid
Dithiobenzoic acid
(Benzenecarbodithioic acid)
Dithiocarboxylic acid ester Carbodithio RC=SSR' Dithioate -dithioate

Groups containing phosphorus

[edit]

Compounds that contain phosphorus exhibit unique chemistry due to the ability of phosphorus to form more bonds than nitrogen, its lighter analogue on the periodic table.

Chemical class Group Formula Structural formula Prefix Suffix Example
Phosphine
(Phosphane)		 Phosphino R3P A tertiary phosphine phosphanyl- -phosphane Methylpropylphosphane
Methylpropylphosphane
Phosphonic acid Phosphono Phosphono group phosphono- substituent phosphonic acid Benzylphosphonic acid
Benzylphosphonic acid
Phosphate Phosphate Phosphate group phosphonooxy-
or
O-phosphono- (phospho-) 		substituent phosphate Glyceraldehyde 3-phosphate
Glyceraldehyde 3-phosphate (suffix)
Phosphocholine
O-Phosphonocholine (prefix)
(Phosphocholine)
Phosphodiester Phosphate HOPO(OR)2 Phosphodiester [(alkoxy)hydroxyphosphoryl]oxy-
or
O-[(alkoxy)hydroxyphosphoryl]- 		di(substituent) hydrogen phosphate
or
phosphoric acid di(substituent) ester 		DNA
O‑[(2‑Guanidinoethoxy)hydroxyphosphoryl]‑l‑serine (prefix)
(Lombricine)

Groups containing boron

[edit]

Compounds containing boron exhibit unique chemistry due to their having partially filled octets and therefore acting as Lewis acids.

Chemical class Group Formula Structural formula Prefix Suffix Example
Boronic acid Borono RB(OH)2
Borono- substituent
boronic acid
Phenylboronic acid
Phenylboronic acid
Boronic ester Boronate RB(OR)2
O-[bis(alkoxy)alkylboronyl]- substituent
boronic acid
di(substituent) ester
Borinic acid Borino R2BOH
Hydroxyborino- di(substituent)
borinic acid
Borinic ester Borinate R2BOR
O-[alkoxydialkylboronyl]- di(substituent)
borinic acid
substituent ester
2-Aminoethoxydiphenyl borate
Diphenylborinic acid 2-aminoethyl ester
(2-Aminoethoxydiphenyl borate)

Groups containing metals

[edit]
Chemical class Structural formula Prefix Suffix Example
Alkyllithium RLi (tri/di)alkyl- -lithium

methyllithium

Alkylmagnesium halide RMgX (X=Cl, Br, I)[note 1] -magnesium halide

methylmagnesium chloride

Alkylaluminium Al2R6 -aluminium

trimethylaluminium

Silyl ether R3SiOR -silyl ether

trimethylsilyl triflate

note 1 Fluorine is too electronegative to be bonded to magnesium; it becomes an ionic salt instead.

Names of radicals or moieties

[edit]

These names are used to refer to the moieties themselves or to radical species, and also to form the names of halides and substituents in larger molecules.

When the parent hydrocarbon is unsaturated, the suffix ("-yl", "-ylidene", or "-ylidyne") replaces "-ane" (e.g. "ethane" becomes "ethyl"); otherwise, the suffix replaces only the final "-e" (e.g. "ethyne" becomes "ethynyl").[4]

When used to refer to moieties, multiple single bonds differ from a single multiple bond. For example, a methylene bridge (methanediyl) has two single bonds, whereas a methylidene group (methylidene) has one double bond. Suffixes can be combined, as in methylidyne (triple bond) vs. methylylidene (single bond and double bond) vs. methanetriyl (three double bonds).

There are some retained names, such as methylene for methanediyl, 1,x-phenylene for phenyl-1,x-diyl (where x is 2, 3, or 4),[5] carbyne for methylidyne, and trityl for triphenylmethyl.

Chemical class Group Formula Structural formula Prefix Suffix Example
Single bond R• Ylo-[6] -yl
Methyl group
Methyl radical
Double bond R: ? -ylidene
Methylidene
Triple bond R⫶ ? -ylidyne
Methylidyne
Carboxylic acyl radical Acyl R−C(=O)• ? -oyl
Acetyl

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Functional group

View on Grokipedia
from Grokipedia
In , a functional group is an atom or a group of atoms that imparts similar chemical properties to different compounds in which it occurs, thereby defining the characteristic reactivity and behavior of families of organic molecules. These groups are typically small assemblies of atoms, often two to four in number, that exhibit consistent responses to specific reagents, enabling predictable chemical transformations. Functional groups form the cornerstone of by allowing molecules to be analyzed and synthesized based on their reactive sites rather than their entire structure, which simplifies , prediction of , and reaction planning. This functional group approach treats organic compounds as consisting of an inert framework attached to one or more reactive functional units, dominating the field and facilitating the classification of diverse substances into manageable categories. For instance, the presence of a hydroxyl group (-OH) characterizes alcohols, which are polar and capable of hydrogen bonding, while a (C=O) defines aldehydes and ketones, influencing their reactions. Other prominent examples include:
  • Alkenes and alkynes, featuring carbon-carbon double (C=C) and triple (C≡C) bonds, respectively, which confer unsaturation and enable addition reactions.
  • Carboxylic acids (-COOH), which are acidic due to the carboxyl group and form salts with bases.
  • Amines (-NH₂, -NHR, or -NR₂), nitrogen-containing groups that act as bases and nucleophiles in biological and synthetic contexts.
  • Halides (-X, where X is F, Cl, Br, or I), which serve as leaving groups in substitution and elimination reactions.
The priority of functional groups in IUPAC nomenclature dictates the suffix of a compound's name, with higher-priority groups like carboxylic acids taking precedence over others such as alcohols. This systematic organization underscores the role of functional groups in both theoretical understanding and practical applications, from pharmaceuticals to .

Fundamentals

Definition and Characteristics

In , a functional group is defined as an atom or a group of atoms responsible for the characteristic chemical reactions of the parent molecule, exhibiting similar properties whenever it occurs in different compounds. This structural feature determines the family's physical and chemical behaviors, often independent of the surrounding molecular framework. According to the International Union of Pure and Applied Chemistry (IUPAC), organic compounds typically consist of a relatively unreactive carbon-based backbone combined with one or more functional groups that dictate the compound's reactivity and properties. Functional groups impart specific physical properties, such as polarity and acidity, which influence , points, and intermolecular forces in molecules. For instance, polar functional groups enable hydrogen bonding or dipole-dipole interactions, enhancing solubility compared to nonpolar hydrocarbons. Chemically, they serve as primary sites of reactivity, where reactions preferentially occur due to localized or bond strain; the carbon-carbon in alkenes (denoted as C=C), for example, provides pi electrons that facilitate reactions, distinguishing it from the saturated single bonds in alkanes. These characteristics allow chemists to predict molecular behavior based on the presence of such groups, regardless of the overall molecular size. Understanding functional groups builds on the foundational structure of organic molecules, which are primarily composed of carbon atoms forming chains or rings with single, double, or triple bonds to or other elements. This carbon skeleton provides stability, while functional groups introduce variability in reactivity. Unlike general substituents—such as alkyl or groups that merely modify the parent chain without defining its principal chemical class—functional groups are the reactive moieties that establish the compound's core identity and reaction profile in and synthesis.

Historical Development

The concept of functional groups in chemistry emerged from early observations of reactivity in the late , particularly through Antoine Lavoisier's work on . Lavoisier demonstrated that oxygen plays a central role in processes, interpreting it as a rather than the release of phlogiston, which highlighted how specific elements could impart characteristic reactivity to compounds. This shift laid foundational insights into reactive components within substances, influencing the later recognition of atom groups responsible for similar behaviors across organic molecules. In the , the field advanced significantly with Friedrich Wöhler's 1828 synthesis of from inorganic precursors, which challenged and spurred systematic study of organic structures. Wöhler, collaborating with , contributed to the radical theory, positing that stable groups of atoms—such as the benzoyl radical—act as persistent units in reactions, akin to elements in . This idea was formalized by Jean-Baptiste-André Dumas in the , who expanded the theory to explain substitution reactions in organic compounds, viewing molecules as assemblies of interchangeable radicals that dictate reactivity patterns. Liebig's development of analytical techniques further enabled the identification and of these groups, solidifying their role in organic analysis. The term "functional group" emerged in the late , with its use becoming standardized at the , where rules were established to indicate principal functional groups via suffixes in compound names. Hermann Kolbe's contributions in the emphasized how specific atom assemblages could be manipulated predictably in structural formulas, advancing the alongside contemporaries like Charles Gerhardt. By the late , and Joseph Achille Le Bel independently proposed the tetrahedral arrangement of carbon atoms in 1874, integrating into structural theory and underscoring how functional groups influence spatial arrangements and reactivity. The refined the functional group concept through experimental and theoretical advancements. Spectroscopic techniques, evolving from early UV-visible methods to and NMR spectroscopy in the mid-century, provided direct evidence of group-specific vibrational and magnetic properties, confirming their consistent behaviors across compounds. Concurrently, the advent of in the 1920s, particularly the valence bond and theories developed by , , and others, offered a mechanistic explanation for the electronic delocalization and reactivity inherent to functional groups, bridging empirical observations with atomic-level understanding.

Importance and Applications

Role in Organic Chemistry

Functional groups play a pivotal role in by serving as the primary sites of reactivity within molecules, enabling chemists to predict and generalize chemical behavior across diverse compounds. These groups, consisting of specific atoms or arrangements of atoms, dictate characteristic reactions regardless of the surrounding molecular structure. For example, carbonyl groups (C=O) consistently undergo or oxidation reactions, allowing predictions about how aldehydes or ketones will respond to like reducing agents or nucleophiles. This predictive power stems from the localized electronic properties of functional groups, which influence bond strengths and electron densities, facilitating the classification of compounds into where reactivity patterns are consistent. The structural organization provided by functional groups forms the foundation for systematic study in , as molecules are categorized based on their principal functional group. This approach groups compounds like alcohols (R-OH), which exhibit hydrogen bonding and acidity, separately from ketones (R-C(=O)-R), which are prone to enolization and carbonyl-specific reactions. Such classification simplifies the analysis of reaction mechanisms and synthetic planning, as compounds within the same family share analogous reactivity profiles, allowing chemists to apply established reaction conditions broadly. This organizational principle underpins the development of reaction databases and predictive models in computational . In synthetic routes, functional groups are essential targets for interconversions, where one group is transformed into another to construct desired molecular architectures. These transformations, often involving oxidation, reduction, or substitution, exploit the inherent reactivity of the groups to achieve selectivity. A representative example is the oxidation of a to an , which introduces a reactive carbonyl for further elaboration. This step is crucial in multi-step syntheses, as it allows progression along oxidation ladders while preserving the carbon skeleton. The oxidation of primary alcohols to aldehydes is typically performed using (PCC) in to avoid over-oxidation to carboxylic acids. The general transformation is represented as: \ceR−CH2−OH−>[PCC][CH2Cl2]R−CHO\ce{R-CH2-OH ->[PCC][CH2Cl2] R-CHO} Under these conditions, the reaction proceeds via chromate ester formation and subsequent elimination, yielding the aldehyde in high selectivity. This method exemplifies how functional group interconversions enable precise control in .

Applications in Synthesis and Biology

Functional groups serve as essential handles in , enabling chemists to direct reactivity and construct complex through selective transformations. In multi-step syntheses, protecting groups are commonly employed to temporarily mask reactive functional groups, such as alcohols or amines, preventing unwanted side reactions while allowing modifications elsewhere in the . For instance, the acetal protection of carbonyl groups facilitates the selective manipulation of other sites, a strategy pivotal in assembling intricate structures. This approach proved crucial in the total synthesis of natural products like penicillin V, achieved by John C. Sheehan in 1957, where the β-lactam ring—a strained amide functional group—and the thiazolidine heterocycle were constructed via targeted activations of carboxylic acid and amine groups. The synthesis highlighted how functional groups dictate stereoselectivity and ring closure, yielding the antibiotic in a landmark demonstration of synthetic control over biologically active scaffolds. In biological systems, functional groups underpin the structure and function of biomolecules, with phosphate groups forming the phosphodiester backbone of DNA for genetic stability and information transfer, while amide linkages in peptide bonds connect amino acids in proteins to enable folding and catalysis. Enzyme specificity often relies on precise recognition of these groups; for example, proteases distinguish amide bonds in substrates through hydrogen bonding and steric fit at the active site, ensuring selective hydrolysis. Contemporary applications extend to , where sulfonamide groups mimic substrates to inhibit bacterial folate synthesis, as in sulfamethoxazole, revolutionizing therapy since the 1930s. Advances like have further amplified these uses, particularly through copper-catalyzed azide-alkyne cycloaddition (CuAAC), a bioorthogonal reaction that ligates (R-N₃) and terminal (R'-C≡CH) groups to form stable 1,2,3-triazoles without interfering with living systems. This method, independently reported by Meldal and by Fokin/Sharpless in 2002, enables precise labeling of biomolecules . \ce{R-N3 + R'-C#CH ->[Cu(I) cat.] 1,4-disubstituted-1,2,3-triazole}

Classification and Nomenclature

Classification by Composition

Functional groups in organic chemistry are classified primarily according to their elemental composition, which provides a framework for understanding their structural and reactive characteristics. The main categories encompass hydrocarbons, composed exclusively of carbon and hydrogen atoms; and heteroatom groups, which incorporate elements such as oxygen, nitrogen, sulfur, halogens, and phosphorus. This system organizes functional groups based on the presence and type of heteroatoms or specific bond arrangements that confer distinct chemical behavior, with hydrocarbons acting as the foundational reference point lacking such elements. The rationale for this compositional classification stems from the role of heteroatoms in altering molecular polarity and reactivity through differences in , availability, and bond strengths compared to pure carbon-hydrogen frameworks. In hydrocarbons, baseline reactivity arises from C-H bonds or pi bonds in unsaturated systems, whereas heteroatoms introduce sites for nucleophilic or electrophilic interactions; for example, the electronegative in -X groups create polar C-X bonds susceptible to substitution, and oxygen in >C=O groups enables reactions due to the electrophilic carbonyl carbon. This approach highlights how elemental makeup dictates the group's influence on the overall molecule without overlapping into detailed reactivity profiles. Subgroups within these categories are delineated by specific structural motifs, such as C=C for unsaturated hydrocarbons, -X for halogen-containing groups, and >C=O for carbonyls, each representing a non-exhaustive set of arrangements that define reactivity classes through their atomic connectivity. For instance, the in alkenes introduces unsaturation to the backbone, while the to a provides a potential, and the carbonyl's C=O linkage establishes a key electrophilic center. The following table provides a high-level overview of primary categories by elemental composition, including representative subgroups and general formulas:
CategoryKey Element(s)Representative SubgroupsGeneral Formula
HydrocarbonsC, HAlkanes, Alkenes, AlkynesR-H, R2_2C=CR2_2, RC≡CR
Halogen-ContainingF, Cl, Br, IAlkyl halidesR-X
Oxygen-ContainingOAlcohols, Ethers, CarbonylsR-OH, R-OR', R2_2C=O
Nitrogen-ContainingNAmines, NitrilesR-NH2_2, R-C≡N
Sulfur-ContainingSThiols, ThioethersR-SH, R-S-R
This tabular summary illustrates the compositional diversity while emphasizing structural simplicity in each class.

Nomenclature Principles

In organic nomenclature, the International Union of Pure and Applied Chemistry (IUPAC) defines a strict seniority order for functional groups to ensure unambiguous naming of compounds. This order determines which functional group serves as the principal characteristic group, forming the basis of the parent hydride name and expressed as a suffix, while subordinate groups are cited as prefixes. The seniority is based on criteria such as oxidation state and structural complexity, as outlined in the IUPAC recommendations. The highest-ranking classes include acids and their derivatives, which dictate the parent chain selection. For example, carboxylic s receive the suffix -oic acid, and the carbon of the -COOH group is included in the chain numbering. Lower-ranking groups like alcohols use the suffix -ol only if no higher group is present. When multiple functional groups occur, the chain is chosen to contain the senior group, numbered from the end nearest to it, and subordinate groups receive prefixes such as hydroxy- for -OH or oxo- for =O in ketones when not principal. Multiplicative prefixes (e.g., di-, tri-) are employed for identical groups, with locants assigned to yield the lowest possible numbers. The following table summarizes the seniority order for selected principal functional classes, from highest to lowest priority, with corresponding suffixes (for acyclic compounds) and example prefixes for subordinate use. This order is derived directly from IUPAC's Table 4.1 in the Nomenclature of Organic Chemistry (Blue Book, 2013).
Seniority RankClassSuffix (Principal)Prefix (Subordinate)Example
1Carboxylic acids-oic acidcarboxy-CH₃COOH: ethanoic acid
2Carboxylic esters-oatealkoxycarbonyl-CH₃COOCH₃: methyl ethanoate
3Acid halides-oyl halidehalocarbonyl-CH₃COCl: ethanoyl
4Amides-amidecarbamoyl-CH₃CONH₂: ethanamide
5Nitriles-nitrilecyano-CH₃CN: ethanenitrile
6Aldehydes-alformyl-CH₃CHO: ethanal
7Ketones-oneoxo-CH₃COCH₃: propan-2-one
8Alcohols-olhydroxy-CH₃CH₂OH:
9Amines-amineamino-CH₃CH₂NH₂: ethanamine
10Alkenes-ene-CH₂=CH₂: ethene
11Alkynes-yne-HC≡CH: ethyne
12Alkanes-ane-CH₃CH₃:
For simple alcohols like CH₃CH₂OH, the IUPAC name is , where the two-carbon chain is the parent "" modified by the -ol at position 1 (implied). In contrast, a compound with both a and an alcohol, such as HOCH₂CH₂CH₂COOH, is named 4-hydroxybutanoic ; the group has higher seniority, forming the suffix -oic on a four-carbon chain, with the alcohol as the prefix hydroxy- at the lowest possible after prioritizing the (position 1). IUPAC names often differ from retained common names for familiar compounds, particularly those without complex substituents. For instance, the ketone CH₃COCH₃ is systematically propan-2-one, but the common name acetone is retained for general use. Handling unsaturation follows similar rules: if a principal group coexists with double or triple bonds, the suffix incorporates them (e.g., -enoic acid for unsaturated acids like CH₂=CHCOOH, prop-2-enoic acid), with chain numbering giving the principal group the lowest number, followed by the unsaturation locants.

Common Functional Groups

Hydrocarbon Groups

Hydrocarbon functional groups are the simplest class of functional groups in , consisting exclusively of carbon and atoms, and they form the non-polar skeletal framework of many organic molecules. These groups are derived from and are characterized by their saturated or unsaturated C-C and C-H bonds, which impart stability and hydrophobicity to the compounds they are part of. Unlike functional groups containing heteroatoms, hydrocarbon groups exhibit minimal polarity due to the similar electronegativities of carbon (2.55) and (2.20), resulting in weak intermolecular forces such as dispersion forces. Alkyl groups represent the saturated functional groups, obtained by removing one from an . The general for an is \ceCnH2n+1−\ce{C_nH_{2n+1}-}, where n≥1n \geq 1, and they are classified as primary, secondary, or tertiary based on the number of carbon atoms attached to the carbon bearing the free valence. For example, the (−\ceCH3-\ce{CH3}) is derived from (\ceCH4\ce{CH4}), making it the simplest with n=1n=1. These groups are non-polar and contribute to the overall hydrophobicity of s, as their C-H bonds have low moments. Unsaturated hydrocarbon groups include alkenyl and alkynyl groups, which contain carbon-carbon double or triple bonds, respectively, introducing sites for potential reactivity while maintaining the composition. Alkenyl groups, such as the vinyl (ethenyl) group −\ceCH=CH2-\ce{CH=CH2}, are derived from alkenes by removal of a , with the double-bonded carbons exhibiting sp2sp^2 hybridization and trigonal planar around the unsaturated carbons. The general formula for a simple alkenyl group like ethenyl is \ceC2H3−\ce{C2H3-}, and the arises from the overlap of p orbitals perpendicular to the framework. Alkynyl groups, exemplified by the ethynyl group -\ce{C#CH}, are derived from alkynes and feature spsp-hybridized carbons with linear , where the consists of one and two s formed by p-orbital overlap. These unsaturations alter the and compared to alkyl groups but preserve the non-polar nature of the C-H bonds. Aryl groups are unsaturated functional groups derived from aromatic hydrocarbons, such as the \ceC6H5−\ce{C6H5-}, which is obtained by removing a from (\ce[C6H6](/page/C6H6)\ce{[C6H6](/page/C6H6)}). In aryl groups, the carbon atoms in the ring are sp2sp^2-hybridized, forming a planar hexagonal structure with delocalized pi electrons across six p orbitals, one from each carbon. This delocalization, known as , involves the pi electrons being shared equally among the ring bonds, resulting in all C-C bonds having equal length (approximately 139 pm) and enhanced stability compared to localized double bonds in alkenes. The resonance stabilization energy for is about 36 kcal/mol, making aryl groups particularly resistant to addition reactions that would disrupt the aromatic system. Overall, groups exhibit low polarity and high hydrophobicity, as their non-polar C-H bonds do not form bonds with , leading to poor in aqueous environments and preferential association with non-polar solvents. This property underlies their role as the hydrophobic tails in and . A key reactivity pattern for these groups is their complete in oxygen, producing and ; for (\ceCH4\ce{CH4}), the reaction is \ceCH4+2O2−>CO2+2H2O\ce{CH4 + 2O2 -> CO2 + 2H2O}, releasing approximately 890 kJ/mol of and exemplifying the high calorific value of hydrocarbons as fuels.

Halogen-Containing Groups

Halogen-containing functional groups, also known as haloorganics, feature one or more atoms (, , , or iodine) covalently bonded to a carbon atom, typically replacing a in a framework. These groups introduce significant polarity into molecules due to the substantial differences between carbon (electronegativity 2.5) and the (F: 4.0, Cl: 3.0, Br: 2.8, I: 2.5), creating a dipole moment that makes the carbon atom partially positive and the halogen partially negative. This polarity enhances reactivity compared to nonpolar s, enabling the to serve as leaving groups in various transformations. Alkyl halides, with the general formula R-X where R is an and X is a , exemplify the most reactive halogen-containing functional groups. The C-X bond in these compounds is polarized, with the difference drawing away from carbon, rendering it electrophilic and susceptible to nucleophilic attack. Among halogens, forms the strongest C-X bond (bond dissociation energy approximately 485 kJ/mol), attributed to its highest , which strengthens the bond through enhanced coulombic attraction despite the small atomic size of . In contrast, bonds with , , and iodine weaken progressively (C-Cl: 327 kJ/mol, C-Br: 285 kJ/mol, C-I: 213 kJ/mol), facilitating easier cleavage in reactions. Aryl halides, represented as C₆H₅-X, consist of a halogen directly attached to an sp²-hybridized carbon in a ring. Their reactivity is markedly reduced compared to alkyl halides because resonance from the aromatic ring delocalizes , strengthening the C-X bond and decreasing its polarity, which hinders standard pathways like SN1 or SN2. This resonance stabilization involves overlap of the halogen's p-orbitals with the π-system of the ring, effectively donating electron density back to the carbon-halogen bond. Vinyl halides, featuring a bonded to an sp²-hybridized carbon in a C=C-X arrangement, exhibit similar low reactivity to aryl halides. The sp² hybridization imparts higher s-character (33% s versus 25% in sp³), holding closer to the nucleus and resulting in a shorter, stronger C-X bond that resists nucleophilic approach. This structural feature, combined with the planar geometry around the , sterically and electronically impedes backside attack required for many substitution reactions. The primary reactivity of alkyl halides involves mechanisms, SN1 and SN2, where the acts as a . In SN2 reactions, a attacks the carbon from the back side in a concerted, bimolecular process, leading to inversion of configuration; this pathway favors primary alkyl halides and less sterically hindered systems. SN1 proceeds via a unimolecular rate-determining step forming a intermediate, favored by tertiary alkyl halides in polar protic solvents, followed by capture that can yield . A representative example is the of an alkyl bromide: R-Br+OH−→R-OH+Br−\text{R-Br} + \text{OH}^- \rightarrow \text{R-OH} + \text{Br}^- This equation illustrates the general substitution, where the mechanism (SN1 or SN2) depends on the substrate structure, strength, and .

Oxygen-Containing Groups

Oxygen-containing functional groups are characterized by the presence of oxygen atoms bonded to carbon, imparting significant polarity to molecules due to oxygen's high (3.44 on the Pauling scale). This polarity enables these groups to participate in hydrogen bonding, which influences , boiling points, and intermolecular interactions in organic compounds. Common examples include alcohols, ethers, carbonyls, carboxylic acids, epoxides, and peroxides, each exhibiting distinct reactivity patterns driven by the oxygen's electron-withdrawing effects. Alcohols and phenols feature a hydroxyl group (-OH) attached to a carbon chain (R-OH for alcohols) or an aromatic ring (Ar-OH for ). The -OH group allows for strong intramolecular and intermolecular hydrogen bonding, elevating boiling points compared to hydrocarbons of similar molecular weight; for instance, boils at 78°C versus -42°C for . Alcohols are weakly acidic with pKa values ranging from 15 to 18, depending on the substitution (e.g., pKa 15.5, tertiary alcohols higher), forming ions upon deprotonation. exhibit greater acidity (pKa ~10) due to resonance stabilization of the phenoxide ion by the aromatic ring, enabling reactions like . Both groups contribute to the polarity and solvating properties of molecules in aqueous environments. Ethers consist of an oxygen atom bridged between two alkyl or aryl groups (R-O-R'), lacking a on oxygen and thus unable to form bonds as donors. This results in lower s and limited polarity compared to alcohols, making ethers excellent aprotic solvents like ( 34.6°C). Ethers display low reactivity under neutral conditions, resisting and oxidation, though they can undergo cleavage with strong acids such as HI. Their stability and solvating ability for both polar and nonpolar substances make them invaluable in synthetic chemistry and extractions. Carbonyl groups (C=O) are central to aldehydes (R-CHO) and ketones (R-COR'), where the carbon-oxygen exhibits high polarity, with partial positive charge on carbon and negative on oxygen (dipole moment ~2.3-2.7 D). This polarity activates the carbonyl carbon toward reactions, such as hydration or Grignard addition, where nucleophiles attack the electrophilic carbon, often followed by to restore the tetrahedral intermediate. Aldehydes are more reactive than ketones due to steric hindrance in the latter and the absence of an stabilizing the carbonyl in aldehydes. These groups underpin reactivity in metabolic pathways and synthesis. Carboxylic acids possess both a carbonyl and a hydroxyl group (R-COOH), forming stable dimers through intermolecular hydrogen bonding between the acidic -OH and the carbonyl oxygen of adjacent molecules, which increases boiling points (e.g., acetic acid at 118°C). They are moderately acidic with pKa values of 4-5, dissociating to ions (R-COO⁻) more readily than alcohols due to delocalization of the negative charge. A key transformation is esterification, an acid-catalyzed equilibrium reaction with alcohols: \ceR−COOH+R′−OH⇌[H+]R−COO−R′+H2O\ce{R-COOH + R'-OH ⇌[H+] R-COO-R' + H2O} This reaction, exemplified by the formation of from acetic acid and , is reversible and driven forward by excess alcohol or water removal. Epoxides are three-membered cyclic ethers with an oxygen atom bonded to two adjacent carbons, creating that enhances reactivity as electrophiles. The strained C-O bonds facilitate ring-opening reactions with nucleophiles, often under acidic or basic conditions, leading to anti addition products useful in stereoselective synthesis. Peroxides feature an oxygen-oxygen (R-O-O-R), which is weak (bond energy ~146 kJ/mol) and prone to homolytic cleavage, contributing to their role as oxidizing agents or in compounds, though they exhibit limited stability in organic contexts.

Nitrogen-Containing Groups

Nitrogen-containing functional groups are characterized by the presence of a atom bonded to carbon or , often featuring a of electrons that imparts basicity and nucleophilic properties to the . These groups play a crucial role in due to nitrogen's moderate (3.04 on the Pauling scale), which is lower than oxygen's (3.44), allowing the to be more available for or nucleophilic attack compared to oxygen analogs like alcohols or ethers. Amines represent the simplest and most common nitrogen-containing functional groups, classified by the number of alkyl or aryl substituents attached to the nitrogen atom: primary amines (RNH₂), secondary amines (R₂NH), and tertiary amines (R₃N). The lone pair on nitrogen in amines confers basicity, with aliphatic amines typically exhibiting pK_b values in the range of 3 to 5, corresponding to pK_a values of about 10 to 11 for their conjugate acids. This basicity arises from the ability of the nitrogen lone pair to accept a proton, as illustrated by the protonation of a primary amine: R-NH2+H+⇌R-NH3+\text{R-NH}_2 + \text{H}^+ \rightleftharpoons \text{R-NH}_3^+ The resulting ammonium ion enhances solubility in aqueous media and enables nucleophilic behavior in reactions such as alkylation or acylation./23%3A_Amines/23.01%3A_Relative_Basicity_of_Amines_and_Other_Compounds) Quaternary ammonium salts, formed by exhaustive methylation of tertiary amines followed by treatment with silver oxide to generate the hydroxide, undergo Hofmann elimination upon heating, yielding an alkene and trimethylamine; this E2 reaction favors the less substituted alkene due to steric factors around the bulky nitrogen leaving group./21%3A_Amines_and_Their_Derivatives/21.08%3A_Quaternary_Ammonium_Salts%3A__Hofmann_Elimination) Amides feature a attached to (R-CONH₂ for primary amides), where delocalization between the and the carbonyl π* orbital significantly reduces basicity compared to amines; the pK_a of protonated amides is around -0.5, making them much weaker bases. This also imparts planarity to the group, with the C-N bond exhibiting partial double-bond character and restricted rotation, influencing molecular conformation and stability in peptides and proteins. Unlike the nucleophilic amines, amides are less reactive at due to this delocalization, though the carbonyl carbon remains electrophilic./23%3A_Amines/23.01%3A_Relative_Basicity_of_Amines_and_Other_Compounds)/09%3A_Organic_Chemistry/9.09%3A_Nitrogen-Containing_Compounds-_Amines_and_Amides) Nitriles contain a carbon-nitrogen (R-C≡N), where the high polarity of the C≡N bond—stemming from nitrogen's —renders the carbon atom electrophilic and the group overall polar, with a dipole moment of about 3.9 D for . This polarity contributes to higher boiling points than hydrocarbons of similar molecular weight and enables addition reactions at the triple bond, such as to carboxylic acids./Nitriles/Properties_of_Nitriles/Nitrile_Properties) Imines, with the general structure R-CH=NR', feature a carbon-nitrogen double bond analogous to the carbonyl in aldehydes but with reduced basicity; the pK_a of protonated imines is typically 5 to 7, lower than that of amines due to the sp² hybridization of nitrogen, which holds the lone pair in an orbital with more s-character and less availability for protonation. The C=N bond imparts rigidity and polarity, making imines key intermediates in reductive amination and useful in coordinating to metals via the nitrogen lone pair./07%3A_Acid-base_Reactions/7.06%3A_Acid-base_properties_of_nitrogen-containing_functional_groups)

Sulfur-Containing Groups

Sulfur-containing functional groups play a significant role in due to the larger atomic size of sulfur compared to oxygen, which imparts greater and distinct reactivity patterns, such as enhanced nucleophilicity and thiophilic tendencies./Thiols_and_Sulfides/Nucleophilicity_of_Sulfur_Compounds) These groups often exhibit lower and variable oxidation states, leading to versatile transformations not typically seen in their oxygen analogs. Thiols, with the general formula R-SH, are characterized by their moderate acidity, with pKa values around 10, making them more acidic than alcohols but less so than carboxylic acids. This acidity arises from the weaker S-H bond strength relative to O-H bonds, facilitating to form thiolates, which are strong nucleophiles. Low-molecular-weight thiols possess a characteristic foul , often described as garlic-like, due to their volatility and interaction with olfactory receptors./15%3A_Oxidation_and_Reduction_Reactions/15.07%3A_Redox_Reactions_of_Thiols_and_Disulfides) A key reactivity feature of thiols is their oxidation to disulfides, represented by the equation: 2R-SH→R-S-S-R+2H++2e−2 \text{R-SH} \rightarrow \text{R-S-S-R} + 2\text{H}^+ + 2\text{e}^- This two-electron oxidation process can be mediated by mild oxidants like air or iodine and is crucial for forming stable S-S linkages./15%3A_Oxidation_and_Reduction_Reactions/15.07%3A_Redox_Reactions_of_Thiols_and_Disulfides) Sulfides, or thioethers (R-S-R'), serve as sulfur analogs to ethers but display heightened nucleophilicity owing to sulfur's larger size and lower electronegativity, which allows for better orbital overlap in transition states./Thiols_and_Sulfides/Nucleophilicity_of_Sulfur_Compounds) This property enables sulfides to act as soft nucleophiles in reactions with soft electrophiles, such as alkyl halides, forming sulfonium salts. Unlike ethers, sulfides are readily oxidized to higher-oxidation-state derivatives, highlighting their reactivity gradient. Sulfoxides (R₂S=O) and sulfones (R₂SO₂) represent oxidized forms of sulfides, with sulfur in +4 and +6 oxidation states, respectively, compared to -2 in sulfides._UNDER_CONSTRUCTION/14%3A_Thiols_and_Sulfides) Sulfoxides feature a polar S=O bond, conferring chirality when the substituents differ, and they serve as versatile solvents or chiral auxiliaries in synthesis due to their ability to coordinate metals. Sulfones, with two S=O bonds, are more stable and electron-withdrawing, often used to stabilize carbanions in umpolung reactivity. These compounds are typically prepared by controlled oxidation of sulfides using reagents like hydrogen peroxide or mCPBA. Thiocarbonyl groups, exemplified by thioesters (R-C(=O)-SR'), replace the oxygen in carbonyl derivatives with sulfur, resulting in a softer, more nucleophilic sulfur center that enhances reactivity toward hard electrophiles.Complete_and_Semesters_I_and_II/Map%3A_Organic_Chemistry(Wade)/22%3A_Carboxylic_Acid_Derivatives_and_Nitriles/22.09%3A_Thioesters-_Biological_Carboxylic_Acid_Derivatives) This structural modification lowers the barrier for nucleophilic acyl substitution compared to oxygen esters, making thioesters key intermediates in reactions. In , sulfur's ability to form crosslinks is exemplified by its role in , where elemental reacts with unsaturated polymers like to create durable S-S bridges, enhancing elasticity and strength. In biology, thiols such as those in contribute to via bonds, though their detailed roles are explored elsewhere./15%3A_Oxidation_and_Reduction_Reactions/15.07%3A_Redox_Reactions_of_Thiols_and_Disulfides)

Other Heteroatom Groups

Phosphoryl groups, denoted as >, represent a key functional motif in phosphorus-containing compounds, where the phosphorus atom is bonded to oxygen via a and typically to three other substituents, such as in esters of the form (RO)₃P=O. These groups exhibit tetrahedral around the central atom, arising from the arrangement of four oxygen substituents (considering the double bond as a single and a ), which facilitates their role in biological and synthetic contexts. In biological systems, phosphoryl groups are integral to phospholipids, amphipathic molecules that self-assemble into bilayers forming the fundamental structure of cell membranes, thereby regulating the passage of ions and molecules across cellular boundaries./14%3A_Biological_Molecules/14.03%3A_Phospholipids_in_Cell_Membranes) Organoboranes, with the general formula R₃B, feature a tricoordinate atom that imparts strong Lewis acidity due to an empty p-orbital, enabling coordination with nucleophiles and their application in cross-coupling reactions such as the Suzuki-Miyaura coupling, where aryl or alkenyl boranes react with organic halides under to form carbon-carbon bonds. Organometallic functional groups include Grignard reagents, RMgX, where R is an alkyl or aryl group and X is a ; these exhibit carbanion-like reactivity at the carbon attached to magnesium, allowing to electrophiles like carbonyl compounds due to the polarized C-Mg bond. Silanes incorporate -based functional groups such as Si-H or Si-C linkages, where the larger atomic size of compared to carbon results in longer bonds and reduced polarity, leading to lower reactivity toward oxidation and relative to analogous carbon compounds. A prominent example involving is the , which converts carbonyl compounds to alkenes using phosphonium ylides; the reaction proceeds as follows: \ceR3P=CH2+R′2C=O−>R′2C=CH2+R3P=O\ce{R3P=CH2 + R'2C=O -> R'2C=CH2 + R3P=O} This transformation, discovered by Georg Wittig, relies on the nucleophilic attack of the carbon on the carbonyl, forming an oxaphosphetane intermediate that collapses to the and triphenylphosphine oxide.

Properties and Reactivity

Influence on Molecular Properties

Functional groups profoundly shape the physical and chemical properties of organic molecules by introducing specific electronic effects, polarity, and interaction capabilities that dictate behaviors such as points, acidity, and . These influences arise primarily from the group's ability to participate in intermolecular forces or alter , enabling chemists to predict molecular behavior based on functional group presence. For example, polar functional groups like alcohols and carbonyls enhance dipole-dipole interactions and hydrogen bonding, while nonpolar groups favor weaker van der Waals forces. Polar functional groups increase molecular polarity, strengthening intermolecular forces and elevating physical properties like and points. The hydroxyl group (-OH) in enables hydrogen bonding, resulting in a of 78°C, far higher than propane's -42°C, where only dispersion forces operate despite comparable molecular sizes. Similarly, groups (-NH₂) promote dipole interactions, contributing to higher viscosity and in compounds like compared to alkanes. Functional groups modulate acidity and basicity through inductive or effects on electron density. Electron-withdrawing groups, such as , stabilize conjugate bases by pulling electrons, thereby lowering pKa values; (Cl₃CCOOH) has a pKa of 0.7 due to the strong inductive withdrawal by three atoms, rendering it far more ic than acetic acid (pKa 4.76). Conversely, electron-donating groups like alkyl chains raise pKa, reducing acidity in carboxylic acids. Spectroscopic properties provide distinctive signatures for functional groups, aiding identification via characteristic absorption or shift patterns. In infrared (IR) spectroscopy, the carbonyl group (C=O) exhibits a strong stretching absorption at approximately 1700 cm⁻¹, arising from the bond's high dipole moment and vibrational frequency. Nuclear magnetic resonance (NMR) spectroscopy reveals deshielding effects; protons adjacent to electronegative groups, such as those alpha to a carbonyl (CH-C=O), resonate at 2.0-2.5 ppm in ¹H NMR, shifted downfield from alkane protons at 0.9-1.8 ppm due to reduced electron density. Hydroxyl protons typically appear at 1-5 ppm, variable with hydrogen bonding. Solubility patterns hinge on functional group polarity, balancing hydrophilic and hydrophobic tendencies. Polar groups like -OH or -COOH form hydrogen bonds with water, enhancing aqueous solubility; for instance, low-molecular-weight alcohols dissolve readily, while introducing nonpolar chains reduces solubility via the hydrophobic effect. Amphiphilic molecules, featuring polar heads (e.g., sulfonate -SO₃⁻) and nonpolar tails (e.g., alkyl chains), exhibit surface-active properties as surfactants, lowering water's surface tension and forming micelles above critical micelle concentrations to solubilize hydrophobic substances.

Reactivity Patterns and Transformations

Functional groups govern the chemical reactivity of organic molecules, enabling predictable transformations that interconvert one functional group into another through specific mechanistic pathways. These reactivity patterns—such as and elimination at unsaturated sites, nucleophilic substitution at carbonyls, oxidation and reduction of alcohols and carbonyls, and metal-catalyzed cross-couplings—form the foundation of synthetic organic chemistry, allowing chemists to build complex structures from simple precursors. The selectivity of these reactions often stems from the inherent electronic properties of the functional groups, which dictate nucleophilic or electrophilic attack and stabilize key intermediates. A prominent reactivity involves and elimination reactions at unsaturated functional groups, particularly and alkynes. In , hydrogen halides like HBr add across the of an following , where the hydrogen attaches to the carbon bearing more hydrogens, and the bonds to the more substituted carbon, due to the formation of the more stable intermediate. For instance, the reaction of with HBr proceeds as \ceCH2=CH2+HBr−>CH3CH2Br\ce{CH2=CH2 + HBr -> CH3CH2Br}, yielding in high yield under acidic conditions. The reverse process, elimination (e.g., E1 or E2 mechanisms), removes HX from alkyl halides to regenerate the alkene, often requiring a base and , thus enabling reversible interconversions between saturated and unsaturated hydrocarbons. Nucleophilic acyl substitution represents a core transformation for carbonyl-based functional groups, including esters, amides, and acid chlorides, where a displaces a at the acyl carbon. The mechanism proceeds via addition of the nucleophile to the electrophilic carbonyl, forming a tetrahedral intermediate, followed by elimination of the leaving group and reformation of the C=O bond. A classic example is the hydrolysis of an ester, such as ethyl acetate, where water or hydroxide attacks the carbonyl, expelling the alkoxide to produce a carboxylic acid and alcohol: \ceRCOOR′+H2O−>RCOOH+R′OH\ce{RCOOR' + H2O -> RCOOH + R'OH}. This reaction, accelerated under acidic or basic conditions, is pivotal for degrading esters in synthetic and biochemical contexts. Oxidation and reduction reactions provide essential tools for adjusting the of functional groups, particularly oxygen- and nitrogen-containing ones. Primary alcohols can be selectively oxidized to aldehydes using (PCC), a chromium(VI)-based reagent that avoids over-oxidation to carboxylic acids by operating in anhydrous . The transformation, \ceRCH2OH−>[PCC]RCHO\ce{RCH2OH ->[PCC] RCHO}, involves hydride abstraction and proceeds in high yield for benzylic or allylic alcohols, as developed by and in 1975. , conversely, convert carbonyls back to alcohols using agents like , highlighting the interconversions central to functional group manipulation. Cross-coupling reactions, often catalyzed by transition metals, enable the formation of new carbon-carbon bonds between organometallic species and organic halides, expanding the toolkit for functional group interconversions. The , a palladium-catalyzed coupling of aryl or vinyl halides with alkenes, involves , coordination-insertion, and beta-hydride elimination to yield substituted alkenes with high (typically trans). For example, iodobenzene couples with to form styrene, \cePhI+CH2=CH2−>[Pd]PhCH=CH2+HI\ce{PhI + CH2=CH2 ->[Pd] PhCH=CH2 + HI}, under basic conditions in polar solvents, as independently reported by Mizoroki and Heck in the 1970s. This pattern is widely applied in pharmaceutical synthesis due to its tolerance of various functional groups. Orthogonal reactivity patterns allow multiple functional groups within a to undergo selective transformations independently, minimizing the need for protecting groups and enabling efficient multi-step syntheses. This selectivity arises from tailored reaction conditions or catalysts that target one group without affecting others, such as copper-catalyzed couplings orthogonal to palladium-mediated ones. For instance, in polyfunctional substrates, aryl iodides can be coupled via Pd catalysis while amines remain inert, facilitating precise control over reaction sequences. The polarity of functional groups, influencing nucleophilicity and electrophilicity, underpins these patterns by directing site-specific reactivity.

References

  1. https://goldbook.iupac.org/terms/view/F02555
  2. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/functbl.htm
  3. https://chemed.chem.purdue.edu/genchem/topicreview/bp/2organic/function.html
  4. https://www.chem.fsu.edu/chemlab/chm1046course/functional.html
  5. https://open.maricopa.edu/fundamentalsoforganicchemistry/chapter/functional-groups/
  6. http://www.chem.ucla.edu/harding/IGOC/F/functional_group.html
  7. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_I_%28Liu%29/02%253A_Fundamental_of_Organic_Structures/2.04%253A_IUPAC_Naming_of_Organic_Compounds_with_Functional_Groups
  8. https://colapret.cm.utexas.edu/courses/functionalgroups.pdf
  9. https://doi.org/10.1351/pac199466051077
  10. https://dept.harpercollege.edu/chemistry/chm/100/dgodambe/thedisk/qual/9back.htm
  11. https://www.chem.uiuc.edu/GenChemReferences/nomenclature_rules.html
  12. https://www.acs.org/education/whatischemistry/landmarks/lavoisier.html
  13. http://chem125-oyc.webspace.yale.edu/125/history99/4RadicalsTypes/radicals1832-40/Dumas1837.html
  14. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%253A_Organic_Chemistry_%28Vollhardt_and_Schore%29/02._Structure_and_Reactivity%253A_Acids_and_Bases_Polar_and_Nonpolar_Molecules/2.4%253A_Functional_Groups%253A_Centers_of__Reactivity
  15. https://courses.lumenlearning.com/suny-orgbiochemistry/chapter/organic-compounds-with-functional-groups/
  16. https://www.ch.imperial.ac.uk/local/organic/tutorial/aaorgsynthyr2.pdf
  17. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_%28Organic_Chemistry%29/Alcohols/Reactivity_of_Alcohols/The_Oxidation_of_Alcohols/Oxidation_by_PCC_%28pyridinium_chlorochromate%29
  18. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Basic_Principles_of_Organic_Chemistry_%28Roberts_and_Caserio%29/13%253A_Polyfunctional_Compounds_Alkadienes_and_Approaches_to_Organic_Synthesis/13.10%253A_Protecting_Groups_in_Organic_Synthesis
  19. https://pubs.acs.org/doi/10.1021/cr0200769
  20. https://www.semanticscholar.org/paper/THE-TOTAL-SYNTHESIS-OF-PENICILLIN-V-Sheehan-Henery-Logan/3a0210a58fc79f18d87b9032b56c58d58c4b541d
  21. https://bio.libretexts.org/Courses/University_of_California_Davis/BIS_2A%253A_Introductory_Biology_-_Molecules_to_Cell/BIS_2A%253A_Introductory_Biology_%28Easlon%29/Readings/03.4%253A_Functional_Groups
  22. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/enzyme-specificity
  23. https://pmc.ncbi.nlm.nih.gov/articles/PMC8046889/
  24. https://openstax.org/books/organic-chemistry/pages/3-1-functional-groups
  25. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Basic_Principles_of_Organic_Chemistry_(Roberts_and_Caserio)/02%3A_Structural_Organic_Chemistry/2.03%3A_Classification_by_Functional_Groups
  26. https://iupac.org/wp-content/uploads/2021/06/Organic-Brief-Guide-brochure_v1.1_June2021.pdf
  27. https://iupac.qmul.ac.uk/BlueBook/P4.html
  28. https://pubchem.ncbi.nlm.nih.gov/compound/10413
  29. https://pubchem.ncbi.nlm.nih.gov/compound/Acetone
  30. https://opentextbc.ca/introductorychemistry/chapter/hydrocarbons/
  31. https://goldbook.iupac.org/terms/view/A00228
  32. https://chem.libretexts.org/Courses/Heartland_Community_College/HCC%253A_Chem_162/22%253A_An_Introduction_to_Organic_Chemistry/22.2%253A_Alkanes%252C_Cycloalkanes%252C_Alkenes%252C_Alkynes%252C_and_Aromatics
  33. https://goldbook.iupac.org/terms/view/A00464
  34. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_%28Physical_and_Theoretical_Chemistry%29/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Intermolecular_Forces/Hydrophobic_Interactions
  35. https://energyeducation.ca/encyclopedia/Methane
  36. https://chemserv.centre.edu/muzyka/organic/jsmol/alhalrx1.htm
  37. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/chapt12.htm
  38. https://www.wiredchemist.com/chemistry/data/bond_energies_lengths.html
  39. https://web.pdx.edu/~wamserc/C336S02/23%2C24notes.htm
  40. https://ocw.uci.edu/upload/files/chapter_7_chem_51a_f14.pdf
  41. https://www.chem.uci.edu/files/smith_textbook/smi96656_c07_001_034.pdf
  42. https://cactus.utahtech.edu/smblack/chem2310/ch9/LG_key_Ch9.pdf
  43. https://crab.rutgers.edu/~alroche/Ch06.pdf
  44. https://web.pdx.edu/~wamserc/CH331F96/notes/Ch8notes.htm
  45. https://pubchem.ncbi.nlm.nih.gov/compound/Propane
  46. https://www.chem.indiana.edu/wp-content/uploads/2018/03/pka-chart.pdf
  47. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/alcohol2.htm
  48. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/aldket1.htm
  49. https://pressbooks.lib.jmu.edu/chemistryatoms/chapter/aldehydes-ketones-carboxylic-acids-and-esters/
  50. https://www.monash.edu/student-academic-success/chemistry/reactions-of-organic-compounds/organic-reactions-and-synthesis-pathways/organic-reactions-esterification-and-transesterification
  51. https://www.oit.edu/sites/default/files/document/chapter-1-7.pdf
  52. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/03%3A_Organic_Compounds-_Alkanes_and_Their_Stereochemistry/3.01%3A_Functional_Groups
  53. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/24%3A_Amines_and_Heterocycles/24.03%3A_Basicity_of_Amines
  54. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/special2.htm
  55. https://web.pdx.edu/~wamserc/C334F99/9notes.htm
  56. https://www.sciencedirect.com/topics/engineering/sulfur-vulcanization
  57. https://chemistry.ucsd.edu/undergraduate/student-resources/CHEM40-Chapter09-UCSD-ED-23-24.pdf
  58. https://pubs.acs.org/doi/10.1021/bk-2016-1236.ch001
  59. https://chemed.chem.purdue.edu/genchem/topicreview/bp/2organic/grignard.html
  60. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/17%3A_Alcohols_and_Phenols/17.05%3A_Alcohols_from_Carbonyl_Compounds_-_Grignard_Reagents
  61. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/silanes.htm
  62. https://open.maricopa.edu/fundamentalsoforganicchemistry/chapter/intermolecular-forces/
  63. https://chem.libretexts.org/Courses/Kenyon_College/Chemistry_231_and_232_-_Kenyon_College_%28Getzler_Hofferberth_and_Hunsen%29/8%253A_Hydroxy_of_Functional_Group%253A_Alcohols%253A_Properties_Preparation_and_Strategy_of_Synthesis/8.2%253A_Structural_and__Physical__Properties_of_Alcohols
  64. https://wou.edu/chemistry/courses/online-chemistry-textbooks/ch103-allied-health-chemistry/ch103-chapter-5-covalent-bonds-organic-functional-groups-and-biological-molecules/
  65. https://www.uvm.edu/~jgoldber/courses/chem36/NewFiles/PSSolutions/chap16asolns.pdf
  66. https://www.chem.uci.edu/files/smith_textbook/smi96656_c19_001_022.pdf
  67. https://chem.libretexts.org/Courses/Athabasca_University/Chemistry_350%253A_Organic_Chemistry_I/12%253A_Structure_Determination-_Mass_Spectrometry_and_Infrared_Spectroscopy/12.07%253A_Interpreting_Infrared_Spectra
  68. https://sites.science.oregonstate.edu/~gablek/CH335/Chapter10/ChemicalShift.htm
  69. https://open.maricopa.edu/fundamentalsoforganicchemistry/chapter/6-6-1h-nmr-spectra-and-interpretation/
  70. https://www.monash.edu/student-academic-success/chemistry/structure-and-properties-of-organic-compounds/properties-and-trends-of-organic-compounds
  71. https://digitalcommons.lib.uconn.edu/context/dissertations/article/7147/viewcontent/PhD_Dissertation.pdf
  72. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/addene1.htm
  73. https://crab.rutgers.edu/~alroche/Ch08.pdf
  74. https://www.vanderbilt.edu/AnS/Chemistry/Rizzo/Chem220b/Ch20.pdf
Add your contribution
Related Hubs
Contribute something
User Avatar
No comments yet.