Relative stabilities and molecular structures of the geometrical isomers of alpha,alpha '-dioxasubstituted cycloalkylidenecycloalkanes. A DFT study

The relative stabilities and molecular structures of the geometrical isomer s of seven alpha,alpha'-dioxa derivatives of cycloalkylidenecycloalkanes wi th 3- to 6-membered rings have been studied by DFT calculations at the B3LY P/6-31G* level of theory. In each case, the E form was calculated to have t he lower total energy. The relative energy of the Z isomer proved to increa se regularly with increasing sizes of the two heterocyclic rings, ranging f rom 1.1 to 13.8 kJ mol(-1) on going from the 3,3- to the 6,6-membered rings . Intermediate values of the relative energy were calculated for the Z form s of compounds containing two dissimilar rings. The relative energy of the Z isomer was found to be proportional to d(-9.3), where d = the distance se parating the two O atoms of the Z compound. The molecular structures, elect ric dipole moments, and atomic charges on the O atoms are also discussed.