Intramolecular hydrogen bonding in 2-nitromalonaldehyde: Infrared spectrum and quantum chemical calculations

2-Nitromalonaldehyde (NO(2)MA), a simple compound to study the intramolecular hydrogen bond, has been synthesized and deuterated at the enolated proton. Molecular structure and vibrational frequencies of NO(2)MA have been investigated by means of density functional theory (DFT) calculations. The geometrical parameters obtained in the B3LYP level using 6-31G**, 6-311G**, and 6-311 + + G** basis sets and compared with the corresponding parameters of malonaldehyde (MA). Frequencies calculated at B3LYP level using the 6-311 G** and 6311 + + G** basis sets are in good agreement with the corresponding experimental results for light and deuterated compounds in CCl4/CS2 solution. The percentage of deviation of the bond lengths and bond angles was used to give a picture of the normal modes, and serves as a basis for the assignment of the wavenumbers. Theoretical calculations show that the hydrogen bond strength of NO(2)MA is slightly stronger than that of MA, which is in agreement with the spectroscopic results. The observed nu OH/nu OD and gamma OH/gamma OD appears at about 2880/2100 and 911/695 cm-(1) respectively, are consistent with the calculated geometry and proton chemical shift results. To investigate the effect of NO2 group on the hydrogen bond strength, the charge distributions, steric effects, and electron delocalization in NO(2)MA and MA were studied by the Natural Bond Orbital (NBO) method for optimized model compounds at B3LYP/6-311 + + G** level of theory. The results of NBO analysis indicate that the electron-withdrawing effect of NO2 group decreases the hydrogen bond strength, but the steric and resonance effects increase the strength of the bond. (c) 2005 Elsevier B.V. All rights reserved.