Theoretical study of annulenes structure [14], [16] and [18] annulenes

The quantum-chemical methods EHT, CNDO/2, MINDO/2 and the method of empirical potentials have been used for calculation of equilibrium geometry of six isomers of [14] annulene, four isomers of [16], and three isomers of [18] annulenes. The bond strengths and degree of delocalization are characterized by the overlap populations and the Wiberg indices. Relative stabilities have been determined by comparison of enthalpies of formation calculated by the MINDO/2 and empirical potential methods. Influence of internal strain of the molecules on their stability lowering is discussed. The degree of aromaticity has been determined by calculation of several aromaticity indexes.