525575-07-9Relevant academic research and scientific papers
Conformational analysis of some N,N-diethyl-2-[(4′-substituted) phenylthio] acetamides
Vinhato, Elisangela,Olivato, Paulo R.,Zukerman-Schpector, Julio,Dal Colle, Maurizio
, p. 738 - 746 (2013/11/06)
The conformational analysis of some N,N-diethyl-2[(4′-substituted) phenylthio]acetamides bearing the substituents OMe 1, Me 2, H 3, Cl 4, Br 5 and NO2 6, was performed by vCO IR analysis, along with B3LYP/6-311++G(d,p) and Polarisable Continuum Model (PCM) calculations, as well as NBO analysis for 1,3, and 6 and X-ray diffraction for 4. The results of the calculations indicated the existence of two stable conformation pairs, i.e. gauche (anti; syn) (most stable) and cis (anti; syn) in the gas phase. The gauche conformers were less polar with respect to the cis ones for 1 and 3, but more polar for 6. The most intense IR carbonyl doublet component observed at the lower frequency can be ascribed to the gauche conformers g(anti; syn) for 3-6 in n-C6H14, which is in agreement with the gauche and cis relative stabilities and frequencies resulting from the PCM calculations. Similarly, the single IR band for 1 and 2 in n-hexane may be attributed to the gauche conformers. The PCM calculations compared well with the IR data for the compounds in solution, showing that there is a progressive increase of the cis/gauche population ratio as the solvent polarity increases. The NBO analysis indicated that the gauche(anti; syn) conformation in the gas phase was stabilized by the relevant LPS4 → πC2=01 * πC2=01 → σ* c3-s4, σC3-S4 → πc2=01 *,πc2=01* → σc3-S4*, and LPO1 → σ C11-H28 orbital interactions, which were absent in the cis(anti; syn) conformer. On the contrary, the cis conformer for derivatives 1, 3, and 6 were stabilized by the σC3-S4 → σC2-N5 * orbital interaction (through bond coupling), along with the additional LPO1 → σS4-C10* interaction for 6. Moreover, the electrostatic repulsion between the C δ+-Sδ- and Cδ+= O δ dipoles (Repulsive Field Effect) contributed to both the larger destabilization and increase of the vCO frequency of the cis conformer with respect to the gauche conformer. X-ray single crystal analysis indicates that compound 4 assumes the c2(anti) conformation in the solid state, which is the conformation obtained by compound 6 in the gas phase. To obtain the largest energy gain, the molecules were arranged in the crystal in a six-molecules synthon mediated by C-H···O and Cl-···Cl interactions, where the chlorine atoms were related by a crystallographic inversion center.
