Cycloheptene

Cycloheptene is a 7-membered cycloalkene with a flash point of −6.7 °C. It is a raw material in organic chemistry and a monomer in polymer synthesis.^{[not in body]} Cycloheptene can exist as either the cis- or the trans-isomer.

Under normal conditions, the cycloheptene double bond forms the cis isomer. However, the unstable trans isomer is an accessible reactive intermediate. Methyl benzoate catalyzes singlet photosensitization; irradiating cis-cycloheptene and it with ultraviolet light at −35 °C produces a detectible trans-cycloheptene population.

The anti-Bredt trans isomer is very strained, and the unsaturated carbons are partly pyramidal. The pyramidalization angle is estimated at 37° and the p orbital misalignment 30.1°. The isomer decomposes facily through a dimolecular, diradical pathway, even at temperatures too low for double-bond rotation.