Autori: V. Chiş, A. Pîrnău, T. Jurcă, M. Vasilescu, S. Simon, O. Cozar, L. David

Editorial: Chemical Physics, 316, p.153-163, 2005.

Rezumat:

In this work, we report a combined experimental and theoretical study on molecular structure and vibrational properties of pyrazinamide
(PZA) molecule, with particular emphasize on its intermolecular hydrogen bonds (HBs). FT-IR/ATR, Raman and NMR
spectroscopic techniques were coupled with theoretical calculations performed at B3LYP and BLYP levels of theory, in conjunction
with 6-31G(d) and cc-pVDZ basis sets. The influence of intermolecular interactions effects on molecular properties have been considered
by calculations performed on PZA dimer. The theoretical geometrical parameters (i.e. bond length: 2.895 A ˚ and bond angle:
178.4
of the intermolecular HB are in excellent agreement with the experiment and suggest a moderate, mostly electrostatic interaction.
This is also sustained by the calculated intermolecular interaction energy of 13.82 kcal/mol which is in line with the corresponding
values for the strongly bound HB dimers formed by N–H


C@O bonds.
All the experimental vibrational bands have been discussed and assigned to normal modes or to combinations and overtones on
the basis of B3LYP and BLYP calculations. With respect to the study of Kalkar et al. and Wang et al. [Spectrochim. Acta, 45A
(1989) 641; Spectrochim. Acta, 56A (2000) 2637.], some modes have been reassigned in the light of present theoretical results. It
is also shown that a very good quantitative agreement between the experimental and calculated chemical shifts both for 1H and
13C nuclei can only be reached by modelling the intermolecular interactions. Moreover, theoretical and experimental NMR data
suggest that only one of the two protons of NH2 group is involved in intermolecular hydrogen bonds.
 2005 Elsevier B.V. All rights reserved.

Cuvinte cheie: Pyrazinamide; FT-IR/ATR; Raman; NMR; DFT; Intermolecular hydrogen bond