Electron spin densities in alternant hydrocarbon mononegative and mono-positive ions and in odd alternant hydrocarbon radicals

Abstract

A comparison is made between MO calculations of electron spin densities in alternant hydrocarbon mono-negative and mono-positive ions and in odd alternant hydrocarbon radicals. For the positive and negative ions the Hückel MO treatment leads to satisfactory results, whereas for radicals configuration interaction must be taken into account. In a preliminary communication McConnell and Chesnut (see ref [14]) also noticed the necessity of π-π interaction in the MO calculations of electron spin densities of hydrocarbon free radicals. In this way negative spin densities are found for those carbon atoms in the radical at which in the non-bonding MO the electron densities are zero. This difference between alternant ions and radicals is due to the fact that in the singly charged ions the odd electron (‘positive hole’) may approximately be considered to move in the electrostatic field of the neutral carbon atoms of the hydrocarbon molecule, whereas in odd alternant hydrocarbon radicals the odd electron forms an integral part of the neutral system.