Planarity of conjugated cyclic systems and prediction of rotational constants : ab initio and semi-empirical calculations of some cross-conjugated compounds

Abstract Ab initio and semi-empirical calculations have been carried out on six cyclic cross-conjugated compounds: fulvene, cyclopentadienone, 2,5-cyclohexadienone, 4,4-dimethyl-2,5-cyclohexadienone, 3-methylene-1,4-cyclohexadiene and 3,3-dimethyl-6-methylene-1,4-cyclohexadiene. The results are compared with experimental data as far as it is available.