Vibrational assignment of alpha-cyanoacetylacetone

The infrared and Raman spectra of alpha -cyanoacetylacetone have been analy zed by the aid of ab initio calculations at post-Hartree-Fock (MP2) and den sity functional theory (DFT) levels and by considering the spectral behavio r upon deuteration of the enolated proton. The results are compared with th ose of acetylacetone. The calculated hydrogen bond strength is 16.26 kcal/m ol. It is shown that a strong interaction between C=C stretch and OH in-pla ne bending motions in CNAA as well as other beta -diketones give rise to tw o Raman active lines in 1500 and 1300 cm(-1) regions. The intensity ratio o f these two lines could be used as criteria for the estimation of the intra molecular hydrogen bond strength in the cis-enol form of beta -diketones. ( C) 2001 Elsevier Science B.V. All rights reserved.