Raman and infrared spectra, normal coordinate analysis and ab initio calculations of 4-Amino-2-chloropyrimidine-5-carbonitrile

• Infrared and Raman spectra of 4-amino-5-pyrimidinecarbonitrile (ACPC) were obtained.
• B3LYP and MP2 frequency calculations were carried out for ACPC at the 6-31G* basis set.
• Vibrational interpretations were in good agreement with the calculated wavenumbers.
• Computational and experimental results favor the pyramidal amino form.

The present work reports an experimental and theoretical study of molecular structure of 4-Amino-2-chloropyrimidine-5-carbonitrile (ACPC) in solid phase. Raman and infrared (IR) spectra of ACPC have been recorded in the region of 3600–100 cm−1 and 4000–200 cm−1, respectively. Calculations with the methods of B3LYP and Møller–Plesset second perturbation (MP2) were carried out for structural and vibrational predictions. The computational approaches were tested and adapted by comparing the predicted spectra to results obtained experimentally. In order to assign the calculated frequencies for the recorded ones, a normal coordinate analysis has been performed for vibrations with respect to the nuclei displacements for all the fundamental frequencies. By computing and analyzing, in detail, the infrared and Raman spectra of ACPC, the changes in the vibrational features were probed by identifying two tautomers of ACPC; (i) amino ACPC which could exist in two conformational structures, and (ii) imino ACPC which could exist in four conformational structures. Both computational and spectral results were in favor of the amino tautomer with no evidence for the existence of interconversion between amino and imino forms. Moreover, only one of the amino ACPC conformers was found to be the most stable one where the hybridization of amino group was found to be sp3. The theoretical predictions agree well with the available experimental data, accounting for the interconversion process in the amino/imino functional groups. We demonstrate that vibrational spectroscopy constitutes a powerful tool for studying molecular structure due to its high sensitivity to changes in molecular geometry.

A novel Raman and infrared spectral and computational investigation of 4-Amino-2-chloropyrimidine-5-carbonitrile were carried out using B3LYP and MP2(full) methods at 6-31G(d) basis set. The current study verifies geometry, structure, NH2 barriers and complete vibrational assignments of the investigated molecule in favor of amino conformer with pyramidal NH2 moiety with no evidence for the existence of imino form.Figure optionsDownload as PowerPoint slide