Adenine residue: A normal‐coordinate analysis of the vibrational spectra

The frequencies observed for adenine in the Raman spectra of adenosine monophosphate (AMP) and biopolymers such as poly(A), DNA, and RNA are compared with those calculated for a model compound, 9‐methyladenine, in which the methyl group is taken as a unit mass concentrated on the carbon. The force field used is a Urey‐Bradley field already tested on polycrystalline adenine and its analogs D‐substituted on the nitrogens, on the carbon at position 8, and on both. Assignments for adenine residue Raman bands are proposed and discussed on the basis of observed and calculated D‐shifts. These assignments are examined, in particular, for bands common to both adenine and guanine residues by analysis of their behavior for Raman hypochromism.