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Chemical name cycloheptene
Chemical formula C7H12
Molecular mass 96.17 g/mol
Melting point °C
Boiling point 112-114.7 °C
Density 0.824 g/cm3
CAS number 628-92-2
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Cycloheptene is a 7-membered cycloalkene. It is a raw material in organic chemistry and a monomer in polymer synthesis.


With cycloheptene, the cis isomer is always assumed but the trans isomer does also exist. One procedure for the organic synthesis of trans-cycloheptene is by singlet photosensitization of cis-cycloheptene with methyl benzoate and ultraviolet light at - 35°C. The double bond in the trans isomer is very strained. Part of the steric strain is relieved by pyramidalization of the alkene carbons, the pyramidalization angle is estimated at 37° (compared to a zero angle in an unstrained alkene) and the p-orbital misalignment is 30.1°. Because the barrier for rotation of the double bond in ethylene is approximately 65 kcal/mol (270 kJ/mol and can only be lowered by the estimated strain energy of 30 kcal/mol (125 kJ/mol) present in the trans isomer, trans-cycloheptene should be a stable molecule just as its homologue trans-cyclooctene. In fact it is not and unless the temperature is kept at very low temperatures quick isomerization to the cis isomer takes place. In a 2005 publication [1] it is argued that trans-cycloheptene isomerization occurs by an alternative lower energy pathway. Based on the experimentally observed second order reaction kinetics for isomerization, two trans-cycloheptene molecules in the proposed pathway first form a diradical dimer. The two heptane radical rings then untwist to an unstrained conformation and in the final step the dimer is cleaved again into two cis-cycloheptene molecules. Note that the photoisomerization of Maleic acid to fumaric acid with bromine is also bimolecular.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cycloheptene". A list of authors is available in Wikipedia.
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