Heterocyclic Betaine Derivatives of Alternant Hydrocarbons

Abstract

Publisher Summary This chapter discusses the chemistry of a major group of heterocyclic mesomeric betaines, those which are isoelectronic with odd alternant hydrocarbon anions. The structural types of the heterocycles include N -oxides, N -imides, and N -ylides. The chemistry of these systems with seven conjugated atoms, with eleven conjugated atoms, with thirteen conjugated atoms, with fifteen conjugated atoms, with seventeen conjugated atoms, and with nineteen conjugated atoms is reviewed. The electronic structure of the mesomeric betaines is presented through the perturbation molecular orbital (PMO) model. Frontier orbitals of several betaines are calculated using the Huckel method and the electroselectivity is correctly predicted on the basis of the orbital symmetry. The pericyclic reactions of mesomeric betaines are also presented which include valence tautomerism, dimerization, and cycloadditions. The chemistry of heterocyclic betaines derived from even alternant hydrocarbon dianions is discussed for (1) mesomeric betaines, and (2) cross-conjugated betaines.