CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
congresos y reuniones científicas
Matrix Photochemestry of CH3C(O)SR with R = H, CH3, C(O)CH3: Theoretical Study of RSH∙∙∙H2CCO molecular complexes
LUCIANA C. JUNCAL; A. LORENA PICONE; ROSANA M. ROMANO
Workshop; Resmol, Reactividad y solvatación a nivel molecular; 2011
During the last years our research group in La Plata has been interested in the study of matrix-isolated molecular complexes. The Matrix isolation technique, combined with FTIR spectroscopy, is a powerful tool for the isolation and characterization of small van der Waals molecules. On a previous work Romano et al. have presented the matrix isolation study of CH3C(O)SH (1), CH3C(O)SCH3 (2) and CH3C(O)SC(O)CH3 (3). The matrix photochemistry of these compounds has been shown to result in a multichannel mechanism (Figure 1). The main process to be observed was the photochemical conversion of 1, 2 and 3 into ketene together with the thiol RSH, where R is H, CH3 and CH3CO, depending on the starting compound. The shifts in some of the infrared absorptions of the major products in comparison with the isolated compounds, gave us reasons to believe that the decomposition leads to loose complexes between the ketene and the corresponding thiol, which are necessarily confined to the same matrix cage by the rigidity of the Ar matrix at low temperatures. In this work we present the results of theoretical calculations of 1:1 molecular complexes between H2CCO and RSH that explain the main features of the IR spectra after the photochemical decomposition of 1, 2 and 3. The theoretical calculations were performed using Gaussian 03 program system. The B3LYP density theory (DFT) method was used, in combination with 6-31+G* and aug-cc-pVDZ basis set. The calculations reveal in same cases more than one potential energy minima. The vibrational properties were calculated to confirm that these structures correspond to energy minima with no imaginary frequencies, and to compare the theoretical infrared shifts with the experimental ones. The bonding properties of the complexes have been interpreted by natural bond orbital analysis (NBO) in terms of ?donor-acceptor? interactions.