A theoretical scheme of annulenes aromaticity

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 HOMAW and HOMAM implicitely included. The decrease in aromaticity index with increasing ring size was modelled for [4n+2] and [4n] annulenes by the functions Δ4n+2(N) and Δ4n(N). Two quantities, κd and νs, as the average measures of noncoplanarity and strain have been defined. Significant correlations of the differences Δx(N) - HOMAW and Δx(N) - HOMAM, which represent the decrease in aromaticity index by noncoplanarity and strain, with a function of the parameters κd and νs, 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.