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Neopentane
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| Names | |||
|---|---|---|---|
| Preferred IUPAC name
2,2-Dimethylpropane[2] | |||
| Other names
Neopentane
Tetramethylmethane[1] | |||
| Identifiers | |||
3D model (JSmol)
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| Abbreviations | Me4C | ||
| 1730722 | |||
| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.006.677 | ||
| EC Number |
| ||
| 1850 | |||
| MeSH | neopentane | ||
PubChem CID
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| UNII | |||
| UN number | 2044 | ||
CompTox Dashboard (EPA)
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| Properties | |||
| C(CH3)4 | |||
| Molar mass | 72.151 g·mol−1 | ||
| Appearance | Colorless gas | ||
| Odor | Odorless | ||
| Density |
| ||
| Melting point | −16.5 °C (2.3 °F; 256.6 K) | ||
| Boiling point | 9.5 °C (49.1 °F; 282.6 K) | ||
| 33.2 mg/L | |||
| Solubility | Soluble in ethanol, diethyl ether, carbon tetrachloride | ||
| log P | 3.11 | ||
| Vapor pressure | 146 kPa (at 20 °C)[3] | ||
Henry's law
constant (kH) |
4.7 nmol Pa−1 kg−1 | ||
Refractive index (nD)
|
1.3476 (at 6 °C) | ||
| Thermochemistry | |||
Heat capacity (C)
|
121.07–120.57 J K−1 mol−1 | ||
Std molar
entropy (S⦵298) |
217 J K−1 mol−1 | ||
Std enthalpy of
formation (ΔfH⦵298) |
−168.5–−167.3 kJ mol−1 | ||
Std enthalpy of
combustion (ΔcH⦵298) |
−3.51506–−3.51314 MJ mol−1 | ||
| Hazards | |||
| GHS labelling:[4] | |||
  
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| Danger | |||
| H220, H411 | |||
| P203, P210, P222, P273, P280, P377, P381, P391, P403, P501 | |||
| NFPA 704 (fire diamond) | |||
| 450 °C (842 °F; 723 K)[6] | |||
| Related compounds | |||
Related alkanes
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Related compounds
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Neopentane, also called 2,2-dimethylpropane, is a double-branched-chain alkane with five carbon atoms, with the chemical formula C(CH3)4. Neopentane is a flammable gas at room temperature and pressure which can condense into a highly volatile liquid on a cold day, in an ice bath, or when compressed to a higher pressure.
Neopentane is the simplest alkane with a quaternary carbon, and has achiral tetrahedral symmetry. It is one of the three structural isomers with the molecular formula C5H12 (pentanes), the other two being n-pentane and isopentane. Out of these three, it is the only one to be a gas at standard conditions; the others are liquids.
It was first synthesized by Russian chemist Mikhail Lvov in 1870.[7]
Nomenclature
[edit]The traditional name neopentane, coined by William Odling in 1876,[8] was still retained in the 1993 IUPAC recommendations,[9][10] but is no longer recommended according to the 2013 recommendations.[2] The preferred IUPAC name is the systematic name 2,2-dimethylpropane, but the substituent numbers are superfluous because it is the only possible "dimethylpropane".
A neopentyl substituent, often symbolized by "Np", has the structure Me3C–CH2– for instance neopentyl alcohol (Me3CCH2OH or NpOH). As Np also symbolises the element neptunium (atomic number 93), one should use this abbreviation with care.
The obsolete name tetramethylmethane is also used, especially in older sources.[11][12]
Physical properties
[edit]Boiling and melting points
[edit]The boiling point of neopentane is only 9.5 °C, significantly lower than those of isopentane (27.7 °C) and normal pentane (36.0 °C). Therefore, neopentane is a gas at room temperature and atmospheric pressure, while the other two isomers are liquids.
The melting point of neopentane (−16.6 °C), on the other hand, is 140 degrees higher than that of isopentane (−159.9 °C) and 110 degrees higher than that of n-pentane (−129.8 °C). This anomaly has been attributed to the better solid-state packing assumed to be possible with the tetrahedral neopentane molecule; but this explanation has been challenged on account of it having a lower density than the other two isomers. Moreover, its enthalpy of fusion is lower than the enthalpies of fusion of both n-pentane and isopentane, thus indicating that its high melting point is due to an entropy effect resulting from higher molecular symmetry. Indeed, the entropy of fusion of neopentane is about four times lower than that of n-pentane and isopentane.[13]
1H NMR spectrum
[edit]Because of neopentane's full tetrahedral symmetry, all protons are chemically equivalent, leading to a single NMR chemical shift δ = 0.902 when dissolved in carbon tetrachloride.[14] In this respect, neopentane is similar to its silane analog, tetramethylsilane, whose single chemical shift is zero by convention.
The symmetry of the neopentane molecule can be broken if some hydrogen atoms are replaced by deuterium atoms. In particular, if each methyl group has a different number of substituted atoms (0, 1, 2, and 3), one obtains a chiral molecule. The chirality in this case arises solely by the mass distribution of its nuclei, while the electron distribution is still essentially achiral.[15]
Derivatives
[edit]The alcohol pentaerythritol can be described as the result of replacing one hydrogen in each of the four methyl groups by a hydroxyl (–OH) group.
A linear polymer with alternating neopentane and orthocarbonate groups, which can be described as an ester (pentaerythritol orthocarbonate, white crystalline solid) with formula [(−CH2)2C(CH2−)2 (−O)2C(O−)2]n, was synthesized in 2002.[16]
References
[edit]- ^ Aston, J.G.; Messerly, G.H., Heat Capacities and Entropies of Organic Compounds II. Thermal and Vapor Pressure Data for Tetramethylmethane from 13.22K to the Boiling Point. The Entropy from its Raman Spectrum, J. Am. Chem. Soc., 1936, 58, 2354.
- ^ a b "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 652. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
- ^ "Neopentane | C5H12 - PubChem".
- ^ "Neopentane". pubchem.ncbi.nlm.nih.gov. Retrieved 5 May 2026.
- ^ "Neopentane". pubchem.ncbi.nlm.nih.gov. Retrieved 5 May 2026.
- ^ "Neopentane". pubchem.ncbi.nlm.nih.gov. Retrieved 5 May 2026.
- ^ Zeitschrift für Chemie (in German). Quandt & Händel. 1870.
- ^ Philosophical Magazine. Taylor & Francis. 1876.
- ^ Table 19(a) Acyclic and monocyclic hydrocarbons. Parent hydrocarbons
- ^ Panico, R. & Powell, W. H., eds. (1994). A Guide to IUPAC Nomenclature of Organic Compounds 1993. Oxford: Blackwell Science. ISBN 978-0-632-03488-8.
- ^ Whitmore, Frank C.; Fleming, Geo. H. (1934-09-01). "Preparation of Tetramethylmethane (Neopentane) and Determination of its Physical Constants1". Journal of the American Chemical Society. 55 (9): 3803–3806. doi:10.1021/ja01336a058. ISSN 0002-7863.
- ^ LaCoste, Lucien J. B. (1934-10-15). "The Rotational Wave Equation of Tetramethylmethane for Zero Potential and a Generalization". Physical Review. 46 (8): 718–724. Bibcode:1934PhRv...46..718L. doi:10.1103/PhysRev.46.718.
- ^ Wei, James (1999). "Molecular Symmetry, Rotational Entropy, and Elevated Melting Points". Ind. Eng. Chem. Res. 38 (12): 5019–5027. doi:10.1021/ie990588m.
- ^ Spectral Database for Organic Compounds, Proton NMR spectrum of neopentane Archived 2020-04-14 at the Wayback Machine, accessed 4 Jun 2018.
- ^ Haesler, Jacques; Schindelholz, Ivan; Riguet, Emmanuel; Bochet, Christian G.; Hug, Werner (2007). "Absolute configuration of chirally deuterated neopentane" (PDF). Nature. 446 (7135): 526–529. Bibcode:2007Natur.446..526H. doi:10.1038/nature05653. PMID 17392783. S2CID 4423560.
- ^ Vodak, David T.; Braun, Matthew; Iordanidis, Lykourgos; Plévert, Jacques; Stevens, Michael; Beck, Larry; Spence, John C. H.; O'Keeffe, Michael; Yaghi, Omar M. (2002). "One-Step Synthesis and Structure of an Oligo(spiro-orthocarbonate)". Journal of the American Chemical Society. 124 (18): 4942–4943. Bibcode:2002JAChS.124.4942V. doi:10.1021/ja017683i. PMID 11982342.
External links
[edit]- Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD)
- IUPAC Nomenclature of Organic Chemistry (online version of the "Blue Book")
Neopentane
View on Grokipediafrom Grokipedia
Nomenclature and structure
Names and identifiers
Neopentane is the retained trivial name for the branched alkane with the molecular formula C₅H₁₂, where the "neo-" prefix historically denotes a structure featuring a new or alternative branching pattern, specifically a terminal tert-butyl group attached to a chain. The preferred IUPAC name is 2,2-dimethylpropane. This systematic name was established under modern IUPAC rules to reflect the longest carbon chain of three atoms with two methyl substituents on the central carbon. The name neopentane originated in the 19th century and was retained in the 1993 IUPAC recommendations for general nomenclature but is no longer recommended in the 2013 IUPAC Blue Book, which prioritizes the systematic name for precision and consistency. Common synonyms for this compound include tetramethylmethane, reflecting its structure as a methane molecule substituted with four methyl groups, and occasionally shortened forms like dimethylpropane, though the latter is less precise. These alternative names arise from early organic chemistry conventions emphasizing structural motifs over strict chain-length rules. Key chemical identifiers for neopentane are the CAS Registry Number 463-82-1, the IUPAC International Chemical Identifier (InChI) InChI=1S/C5H12/c1-5(2,3)4/h1-4H3, and the simplified molecular-input line-entry system (SMILES) notation CC(C)(C)C. These standardized codes facilitate database searches, regulatory compliance, and computational modeling in chemical informatics. As one of the three structural isomers of pentane (C₅H₁₂), neopentane contrasts with the linear n-pentane and the singly branched isopentane (2-methylbutane), highlighting its unique highly symmetric, branched configuration centered on a quaternary carbon atom.Molecular geometry
Neopentane has the molecular formula C₅H₁₂ and features a central quaternary carbon atom bonded to four equivalent methyl groups, represented by the structural formula (CH₃)₄C.[1] This arrangement results in ideal tetrahedral geometry at the central carbon, characterized by C–C bond lengths of 1.534 ± 0.003 Å and bond angles of 109.5°.[6] The identical substituents confer Td point group symmetry to the molecule, yielding high overall symmetry and a nearly spherical shape that distinguishes it as the most compact isomer of pentane.[7] The quaternary carbon center in this neo- configuration introduces substantial steric crowding from the four adjacent methyl groups, providing a structural basis for reduced accessibility in potential reactions.[8] Unlike its linear isomer n-pentane, which adopts an extended chain conformation, neopentane's extreme branching promotes denser intermolecular packing due to its symmetric, globular form.[1]Physical properties
Thermodynamic properties
Neopentane is a colorless gas at room temperature and standard atmospheric pressure (25 °C, 1 atm), condensing to a highly volatile liquid below its boiling point of 9.5 °C.[1] Its molar mass is 72.15 g/mol.[1] The melting point of neopentane is -16.5 °C, and its boiling point is 9.5 °C at 1 atm.[1] The density of neopentane is 3.12 kg/m³ for the gas phase at its boiling point and 601 kg/m³ for the liquid phase at the boiling point. Its vapor pressure is 146 kPa at 20 °C.[1] Neopentane exhibits low solubility in water (approximately 33 mg/L at 25 °C), rendering it practically insoluble, but it is soluble in organic solvents such as ethanol and diethyl ether.[1] The critical point occurs at a temperature of 160.6 °C and a pressure of 3.20 MPa.[9]| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -16.5 °C | Standard pressure | PubChem |
| Boiling point | 9.5 °C | 1 atm | PubChem / NIST WebBook |
| Density (gas) | 3.12 kg/m³ | At boiling point | Calculated (ideal gas approx.) |
| Density (liquid) | 601 kg/m³ | At boiling point | Engineering sources |
| Vapor pressure | 146 kPa | 20 °C | PubChem |
| Critical temperature | 160.6 °C | - | NIST WebBook |
| Critical pressure | 3.20 MPa | - | NIST WebBook |
Spectroscopic properties
Neopentane's high tetrahedral (T_d) symmetry results in highly simplified spectra across various spectroscopic techniques, reflecting the equivalence of its four methyl groups. In proton nuclear magnetic resonance (¹H NMR) spectroscopy, all 12 hydrogen atoms are chemically equivalent, producing a single sharp singlet at approximately 0.9 ppm (in CCl₄ solvent), with no splitting observed due to the absence of neighboring protons.[10] In carbon-13 nuclear magnetic resonance (¹³C NMR) spectroscopy, the molecule displays only two signals: one for the central quaternary carbon and one for the four equivalent methyl carbons, typically appearing around 25–30 ppm in the aliphatic region.[11] The infrared (IR) spectrum of neopentane features characteristic aliphatic C-H stretching vibrations as a strong band near 2900 cm⁻¹, along with weaker C-C skeletal deformations in the 1000–1500 cm⁻¹ range.[12] In mass spectrometry (electron ionization), the molecular ion appears weakly at m/z 72, with the base peak at m/z 57 arising from the loss of a methyl radical (CH₃•), and secondary fragments at m/z 41 and 29 from further cleavages.[13] Ultraviolet-visible (UV-Vis) spectroscopy reveals no significant absorption bands for neopentane in the typical 200–800 nm range, as saturated alkanes lack conjugated systems or chromophores capable of π → π* or n → π* transitions, rendering the compound transparent in this spectral region.[1]Synthesis and production
Laboratory synthesis
Neopentane was first prepared in 1870 by Russian chemist Mikhail Lvov, marking an early milestone in the synthesis of branched alkanes.[14] A classic laboratory method for its preparation involves the coupling reaction of methylmagnesium chloride with tert-butyl chloride in toluene at approximately 45°C, as described by Whitmore and Fleming in 1933; this Grignard-based alkylation yields neopentane after hydrolysis and isolation.[15] Alternative routes include hydrogenolysis of neopentyl compounds, such as the high-pressure hydrogenation of neopentanoic acid at elevated temperatures (typically above 200°C with catalysts like nickel or ruthenium), which decarboxylates and reduces the carboxylic acid to the corresponding alkane. Reduction of pentaerythritol derivatives, such as through exhaustive hydrogenation or halogenation followed by reduction, also provides access to neopentane on a small scale.[16] Following synthesis, neopentane is purified by fractional distillation under reduced pressure to separate it from unreacted reagents and byproducts, or by preparative gas chromatography for samples requiring purity exceeding 99.99 mol%.[17] These techniques exploit its low boiling point (9.5°C) and volatility.[18] Yields in laboratory syntheses are typically low (often below 50%), primarily due to steric hindrance around the quaternary carbon center, which impedes nucleophilic attack and promotes elimination side reactions; all procedures require an inert atmosphere, such as nitrogen or argon, to avoid oxidation or moisture-induced decomposition of organometallic intermediates.[15]Industrial production
Neopentane is primarily produced on an industrial scale through the demethylation of higher neoalkanes, such as neohexane (2,2-dimethylbutane) or neoheptane, via catalytic cracking processes. These methods employ zeolite-based catalysts in reactors, often under controlled temperatures and pressures to optimize yield, as detailed in processes developed around 2018 that focus on efficient isomer conversion from C6-C8 feedstocks.[19][20] Additionally, neopentane is obtained as a minor byproduct during petroleum refining and natural gas processing, where it constitutes a small fraction of the C5 hydrocarbon stream separated from crude oil fractions or syngas-derived products.[21][1] Separation from the C5 mixture, which includes n-pentane and isopentane, typically involves fractional distillation exploiting neopentane's lower boiling point of approximately 9.5°C, or adsorption techniques using molecular sieves such as zeolite Y to achieve selective isolation of the highly branched isomer.[1][22] Due to its niche applications, neopentane production remains low-volume, with global market estimates indicating a value of approximately USD 150 million in 2024, projected to reach USD 300 million by 2033.[23] Recent technological advancements focus on improving production efficiency and reducing environmental impact.[24] For industrial use, neopentane is purified to greater than 99% via fractional distillation or advanced adsorption, ensuring removal of linear pentane impurities that could affect performance in downstream processes.[25]Chemical properties
Stability and reactivity
Neopentane exhibits high chemical stability as a branched alkane, lacking weak bonds or functional groups that would promote reactivity under ambient conditions. Its tetrahedral (Td) symmetry and steric hindrance from the quaternary central carbon atom contribute to this inertness, making it unreactive toward most common reagents at room temperature.[26][27] The compound is inert to dilute acids, bases, and oxidizing agents, showing no significant reaction even upon prolonged exposure due to the absence of accessible sites for nucleophilic or electrophilic attack. This resistance underscores its utility as a model compound in studies of steric effects on molecular interactions.[28] Thermally, neopentane remains stable up to approximately 500°C but undergoes decomposition above this temperature primarily through C-C bond cleavage, yielding methane and isobutene as major products in a radical chain mechanism suppressible by nitric oxide. This high thermal threshold has made it a valuable probe for investigating steric influences in catalytic processes.[29][30] In the presence of high-pressure hydrogen and metal catalysts such as platinum, neopentane undergoes hydrogenolysis via stepwise loss of methyl groups, initially forming isobutane and methane, with further fragmentation possible under more forcing conditions. This pathway highlights the role of catalytic surfaces in overcoming the steric barriers inherent to its structure.[31][32] Isomerization to other pentane isomers, such as isopentane, occurs over acidic catalysts but proceeds slowly owing to the difficulty in generating a carbocation at the quaternary carbon center, often competing with hydrogenolysis in bifunctional systems.[33][34]Combustion and oxidation
Neopentane undergoes complete combustion in oxygen to produce carbon dioxide and water, following the balanced equation:
with a standard enthalpy of combustion of -3514.1 kJ/mol for the gas phase at 298 K.[18]
This reaction exhibits clean-burning characteristics, producing minimal soot due to the highly branched structure that favors complete oxidation, alongside a high heat release consistent with its exothermic enthalpy. Neopentane's combustion has been extensively studied in alkane oxidation kinetics, particularly for understanding low-temperature pathways, cool flames, and negative temperature coefficient behavior in jet-stirred reactors and flow systems.[35][36]
Partial oxidation of neopentane under controlled conditions, such as in low-temperature gas-phase reactions, yields small amounts of oxygenated products including alcohols like methanol and tert-butanol, and aldehydes like formaldehyde and acetone. However, selectivity is low and inefficient owing to the molecule's branching, which promotes radical rearrangements and favors fragmentation over stable partial oxidation intermediates.[37]
Key oxidative derivatives include neopentyl alcohol ((CH₃)₃CCH₂OH), formed as an initial primary substitution product via hydrogen abstraction and oxygen addition at a methyl group, though its yield is limited by steric hindrance in subsequent steps. Pentaerythritol (C(CH₂OH)₄) represents a fully hydroxylated derivative, achieved conceptually through multi-step oxidation and hydroxylation of all methyl groups on the neopentane core, serving as a polyol precursor in materials. In 2002, a linear oligo(spiro-orthocarbonate) polymer incorporating pentaerythritol units alternating with orthocarbonate linkages, with repeating formula [−O−CH₂−C(CH₂−O−)₃−C(−O−)₄−]ₙ, was synthesized via condensation of pentaerythritol and tetraethyl orthocarbonate at 260 °C, offering potential in expanding polymer materials science applications.[38]