title: Conjugation and hyperconjugation in conformational analysis of cyclohexene derivatives containing an exocyclic double bond.
abstract: The equilibrium geometry, ring-inversion pathway barriers for analogues of cyclohexene with an exocyclic double bond have been studied using the MP2/6-311 G(d,p) level of theory. The equilibrium conformation of the ring depends on conjugation between the endocyclic and exocyclic double bonds. Interactions between conjugated double bonds include the pi-pi conjugation and interactions between the lone pair of the heteroatom of the exocyclic double bond and the sigma-antibonding orbital of the endocyclic single bond. In the case of the tetrahydrocycles with double bonds separated by a methylene group the balance between the pi --> sigma* hyperconjugation interactions between the exocyclic double bond and the neighboring methylene group and the n --> sigma* interaction between the lone pair of the heteroatom and the sigma-antibonding orbitals of the C(sp(2))-C(sp(3)) bond determine the geometrical parameters of the ring. The character of the potential-energy surface around the saddle point depends on the position of the exocyclic double bond and the orientation of the hydrogen atom attached to the heteroatom of the V group of the periodic table in the tetrahydrocycles with double bonds separated by a methylene group.
authors.affiliation: STC Institute for Single Crystals, National Academy of Sciences of Ukraine, 60 Lenina Avenue, Kharkiv 61001, Ukraine.
authors.forename: Svetlana V
authors.initials: SV
authors.lastname: Shishkina
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Shishkin
authors.forename: Sergey M
authors.initials: SM
authors.lastname: Desenko
authors.forename: Jerzy
authors.initials: J
authors.lastname: Leszczynski