Experimental and ab initio MO studies on the IR spectra and structure of cyanoacetamide, its carbanion and dianion

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 1998-06, Vol.54 (6), p.843-853
• Main Authors: Binev, Ivan G., Stamboliyska, Bistra A., Binev, Yuri I.
• Format: Article
• Language: English
• Subjects: Ab initio force field; Carbanion; Conformation; Cyanoacetamide; Dianion
• ISSN: 1386-1425
• DOI: 10.1016/S1386-1425(98)00008-0

The structures of cyanoacetamide NC–CH 2–CONH 2, its carbanion NC− CH−CONH 2 and dianion NC− CH−CO NH , and of their perdeutero and 15N labelled analogues have been studied by means of both IR spectra and ab initio HF 6-31G and 6-31+G(d) calculations. Both the spectral and structural changes, accompanying the conversion of cyanoacetamide into the carbanion, spread over the whole molecule; the carbanion → dianion changes are localized mainly within the carboxamido group. The theory predicts qualitatively well the strong frequency decreases (165 and 247 cm −1) and the strong intensity increases (29 fold and 1.7 fold) of the CN and CO stretching bands respectively, resulting from the conversions studied. The first (carbanionic) electric charge is delocalized over the methide (0.36 e −), carboxamide (0.33 e −) and cyano (0.31 e −) groups; the greater part (0.74 e −) of the second (nitranionic) charge remains localized within the carboxamido group. The possible conformers of the species studied are also discussed. The anionic species exist as ion pairs in dimethyl sulfoxide solutions.