Planar valence force constants and assignments for pyrimidine derivatives

Abstract

Overlay calculations have been carried out to obtain a set of transferable valence force constants for the planar modes of pyrimidine derivatives. A 42 parameter force field was adjusted to reproduce 233 experimental frequencies of 10 molecules. Computations were based on previous work on isotopic analogs of uracil and cytosine, and new data on thymine, 1-methylthymine, 1-methyluracil, and N-deuterated analogs. The average frequency error was below one percent. Assignments and characteristic frequencies are discussed on the basis of the potential energy distribution.