Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

An aromaticity scheme for annulenes is developed and applied on set of [6] to [18]annulenes. The dependence of annulenes aromaticity on the ring size, noncoplanarity and strain is considered which factors are in the aromaticity indices HOMA_W and HOMA_M implicitely included. The decrease in aromaticity index with increasing ring size was modelled for [4n+2] and [4n] annulenes by the functions Δ_4n+2(N) and Δ_4n(N). Two quantities, κ_d and ν_s, as the average measures of noncoplanarity and strain have been defined. Significant correlations of the differences Δ_x(N) - HOMA_W and Δ_x(N) - HOMA_M, which represent the decrease in aromaticity index by noncoplanarity and strain, with a function of the parameters κ_d and ν_s, have been obtained. The quantitative results show that not only the [4n]annulenes, but also the large part of the [4n+2]annulenes are antiaromatic, even for the presence of noncoplanarity and strain in the molecules.