Theoretical studies of force fields and IR spectra of isocytosine

Abstract

The optimized geometries, complete harmonic force fields, and infrared intensities of isocytosine tautomers, amino-hydroxy and amino-oxoN(1)H, were calculated at the ab initio Hartree–Fock level using the 6-31G* basis set. The theoretical force fields were scaled by empirical scale factors, which were determined by fitting to the IR spectrum of the amino-oxo form and were then transferred to the amino-hydroxy form. The average deviations between experimental and computed frequencies are 7.6 cm−1 for amino-oxo and 9.5 cm−1 for amino-hydroxy, respectively. The assignments of the fundamental frequencies and the transferability of the force constant scale factors are also presented. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 53–60, 1999