The MCD spectra of some 8-azapurines

The magnetic circular dichroism spectra of 9-methyl-8-azapurine and of 7-, 8-, and 9-methyl-8-azaadenine have been found to be well resolved; as many as four distinct electronic bands are observable in the 200–350 nm spectral region. CNDO calculations indicate that * excitations are responsible for almost all of the MCD intensity. A comparison of four different parameterizations shows that a modification of Del Bene and Jaffé's CNDO/S procedure correctly predicts, with one exception, the sign of the observed B-terms and is therefore the most satisfactory method.Part LIII in the Stanford Series on Magnetic Circular Dichroism Studies. For Part LII, see J. H. Dawson, J. R. Trudell, R. E. Linder, G. Barth, E. Bunnenberg and C. Djerassi, submitted to Biochemistry.