Cycloheptene

cis-Cycloheptene[1]
IUPAC name (Z)-Cycloheptene
Other names cis-Cycloheptene
Identifiers
CAS number	628-92-2 Y
PubChem	12363
ChemSpider	11857 Y
Jmol-3D images	Image 1
SMILES C\1=C\CCCCC/1
InChI InChI=1S/C7H12/c1-2-4-6-7-5-3-1/h1-2H,3-7H2 Y Key: ZXIJMRYMVAMXQP-UHFFFAOYSA-N Y InChI=1/C7H12/c1-2-4-6-7-5-3-1/h1-2H,3-7H2 Key: ZXIJMRYMVAMXQP-UHFFFAOYAQ
Properties
Molecular formula	C7H12
Molar mass	96.17 g/mol
Density	0.824 g/cm3
Boiling point	112-114.7 °C
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Cycloheptene is a 7-membered cycloalkene with a flash point of -7 C°. It is a raw material in organic chemistry and a monomer in polymer synthesis. Cycloheptene can exist as either the cis- or the trans-isomer.

cis-Cycloheptene	trans-Cycloheptene

trans-Cycloheptene

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.^[2] The double bond in the trans isomer is very strained.^[3] 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°.^[2] 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 very low, quick isomerization to the cis-isomer takes place. In a 2005 publication, it is argued that trans-cycloheptene isomerization occurs by an alternative lower energy pathway.^[2] 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.

References

1. ^ Cycloheptene at Sigma-Aldrich
2. ^ ^{a b c} Michael E. Squillacote, James DeFellipis, and Qingning Shu How Stable Is trans-Cycloheptene? J. Am. Chem. Soc.; 2005; 127(45) pp 15983 - 15988; (Article) DOI: 10.1021/ja055388i Abstract
3. ^ D. Cain, D. M. Pawar and E. A. Noe, "Conformational studies of trans-cycloheptene, trans-cycloheptene oxide, and trans-bicyclo [5.1.0] octane by ab initio calculations", Journal of Molecular Structure: THEOCHEM, volume 674, issues 1-3, April 2004, Pages 251-255

External links

• MSDS