Unusual spectroscopic behaviour of the carbonyl and carbon-carbon double-bond groups in the infrared spectra of simple nitroenaminoketone derivatives

The assignment of the vibrational spectra of several isomers of the simple nitroenamine Me(H)N-C(H)=C(NO2)COMe has been theoretically examined (DFT at the B3LYP level using cc-pvtz basis sets) and a normal mode analysis of vi brations has been undertaken. Contrary to the usually expected, analysis of the computed IR spectra shows the inversion of the carbonyl stretching ban d and the 'enamine band' (a coupled mode that is mainly a combination of th e C=C and C-N stretchings) for the configurational isomer where the amino a nd carbonyl groups are forming an intramolecular hydrogen bonding. (C) 2000 Elsevier Science B.V. All rights reserved.