Vibrational spectra and structure of N-(4-cyanobenzylidene)-aniline, its N-15 and D-5 isotopomers and their monomeric dianions: an experimental and ab initio study

The structure of both N-(4-cyanobenzylidene)-aniline molecule and its monom eric dianion has been studied by means of vibrational spectra and ab initio calculations. The assignment of the fundamental frequencies of the studied Schiff base and its isotopic analogues has been performed on the basis of the infrared and Raman spectra and theoretical data. The band position of t he C=N double bond in the monomeric dianion of the studied compound has bee n determined based on the isotopic frequency shift of the respective N-15-l abeled in azomethine group and D-5-labeled in aniline ring isotopomers: the conversion of the N-(4-cyanobenzylidene)-aniline molecule to the monomeric dianion leads to more than 300 cm(-1) frequency decrease of the nu(C=N) ba nd. The theory predicts quite well the structural changes accompanying the conversion of N-(4-cyanobenzylidene)-aniline to its monomeric dianion; the electronic density distribution is spread over the whole molecule. (C) 1999 Elsevier Science B.V. All rights reserved.