An E.S.R. study of some nitrogen substituted free radicals

Abstract

An E.S.R. study of the reaction between 1,4-benzoquinone and sodium azide was made and spectra obtained of some novel triazolo-1,4-semiquinones and also some hitherto unobserved amino-1,4-semiquinones.

These results are interpreted in terms of two competing types of addition of HN₃ to quinone, one being dipolar addition, leading to triazolohydroquinones and the other leading to azidohydroquinones. The decomposition of azidohydroquinones provides a new route to amino-substituted radicals.

Using the McLachlan method for calculating Huckel molecular orbital energies in the anilino radical cation, suitable Huckel parameters for nitrogen were derived. These parameters were tested by calculating spin distributions in the aminophenoxyl series and were then used to confirm the assignments of experimental splitting constants in the amino-and heterocyclic semiquinones.

The occurrence of negative McLachlan spin densities in some of the radicals has been discussed and an attempt has been made to interpret the high-field line broadening in the triazolo-1,4-semiquinone spectrum.