A Computational Study on Azaazulenes

Abstract

All possible aza analogs of azulene, containing from one to three nitrogen atoms in the five-membered ring or from one to five nitrogen atoms in the seven-membered ring, have been theoretically considered to obtain information about their stabilities and aromaticities. Total electronic energy and nucleus independent chemical shift (NICS) data have been used to evaluate stability and aromaticity, respectively. The stabilities of the structures are strongly affected by the positions of the nitrogen atoms. Calculations of azaazulenes show that stability is decreased with close proximity of the nitrogen atoms. When nitrogen in the five-membered ring is adjacent to a ring junction, aromaticity of the cyclopentadienyl anion is reduced and that of the tropylium cation is increased. The number of nitrogen atoms affects the aromaticity of the system.