Five and nine membered (heteronines) heterocyclic molecules. Theoretical approach

The presence or absence of aromaticity in nine membered heterocyclic molecules (heteronines) has been studied from a theoretical point of view (B3LYP/6-311G(2d,p) level). For comparison, the aromaticity of pyrrole, thiophene and furan was analysed. The aromaticity of azonine and thionine is well established along with the problems that arise from the stabilisation of the latter. The origin of oxonine non-aromaticity is discussed in terms of atomic charges and electronegativity. Results for the ion cyclononatetraenide are also reported. Reaction coordinates leading to thionine derivatives are studied. Condensed Fukui functions derived from electronic structure calculations were computed for five and nine membered heterocyclic molecules. These reactivity indices explain the observed products with electrophiles. The stability and the reactivity of these molecules may be understood in terms of the present results.