Planar and nonplanar vibrations of cytosine

The formalism developed in the preceding article is used in a normal coordinate analysis of the pyrimidine base cytosine. The results of both planar and nonplanar vibrations are reported. The model yields 66 frequencies with an average error of about 6.5 cm−1 (ca. 0.5%). The vibrational modes are compared with experimental data and discussed in terms of potential energy distributions and Cartesian displacements. Two isolated low‐frequency (near 200 cm−1) out‐of‐plane modes are predicted in the vicinity of where two such modes are believed to occur. In addition, the model has taken into account the observed coalescence of the torsional and wagging modes of the amino group upon deuteration of the amino group. Recent data from sulfur‐substituted cytosine (2‐thiocytosine) were useful in making assignments.