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 νCO IR analysis, along with B3LYP/6-311++G(d,p) and PCM calculations NBO analysis (for 1, 3 and 6) and X-ray diffraction (for 4). Calculations indicated the existence of two stable conformation pairs i.e. gauche (anti; syn) (most stable) and and cis (anti; syn) in the gas phase. The gauche conformers are the less polar with respect to the cis ones for 1 and 3 while the cis conformers are the less polar relative to the gauche ones for 6. The comparison between experimental (IR) and (PCM) data indicated that the most intense carbonyl doublet component can be ascribed to the gauche conformers g(anti; syn) for 3-6 (IR), in n-C6H14, which are more stable and have a lower calculated frequency than the cis ones. In the same way the single band for 1 and 2 in n-hexane (IR) may be attributed to the gauche conformers. The PCM computations compare well with the IR data in solution, showing that there is a progressive increase of cis/gauche population ratio as the solvent polarity increases. The gauche(anti; syn) preference in the gas phase was ascribed to the combination of LPS4→pi*C2=O1, piC2=O1→σ*C3-S4, σC3-S4→pi*C2=O1, pi*C2=O1→σ*C3-S4 and LPO1→σ*C11-H28 orbital interactions (NBO analysis), which are present only in g(anti; syn) conformers. On the other hand the cis conformers for derivatives 1, 3 and 6 are stabilized by the σC3-S4→σ* C2-N5 orbital interaction (though bond coupling) along with the LPO1→σ*S4-C10 interaction for 6. The gauche preference may be ascribed to the stabilizing orbital interactions in the gauche conformers and also to the destabilization of the cis conformer due to the electrostatic repulsion between Cδ+‒Sδ- and Cδ+=Oδ- dipoles. This Repulsive Field Effect is also responsible for the higher νCO frequency of the cis conformer with respect to that of the gauche conformer in the whole series. X ray single crystal analysis of 4 indicates that this compound adopts in the solid the cis2 conformation obtained in the gas phase for compound 6. In order to obtain the largest energy gain the molecules are arranged in the crystal by six molecules synthons mediated by C-H…O and Cl…Cl interactions. The geometry of this last interaction is called Type I, as the chlorine atoms are related by a crystallographic inversion center.
Conformational analysis of some N,N-diethyl-2-[(4'-substituted)phenylthio] acetamides
DAL COLLE, Maurizio
2013
Abstract
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 νCO IR analysis, along with B3LYP/6-311++G(d,p) and PCM calculations NBO analysis (for 1, 3 and 6) and X-ray diffraction (for 4). Calculations indicated the existence of two stable conformation pairs i.e. gauche (anti; syn) (most stable) and and cis (anti; syn) in the gas phase. The gauche conformers are the less polar with respect to the cis ones for 1 and 3 while the cis conformers are the less polar relative to the gauche ones for 6. The comparison between experimental (IR) and (PCM) data indicated that the most intense carbonyl doublet component can be ascribed to the gauche conformers g(anti; syn) for 3-6 (IR), in n-C6H14, which are more stable and have a lower calculated frequency than the cis ones. In the same way the single band for 1 and 2 in n-hexane (IR) may be attributed to the gauche conformers. The PCM computations compare well with the IR data in solution, showing that there is a progressive increase of cis/gauche population ratio as the solvent polarity increases. The gauche(anti; syn) preference in the gas phase was ascribed to the combination of LPS4→pi*C2=O1, piC2=O1→σ*C3-S4, σC3-S4→pi*C2=O1, pi*C2=O1→σ*C3-S4 and LPO1→σ*C11-H28 orbital interactions (NBO analysis), which are present only in g(anti; syn) conformers. On the other hand the cis conformers for derivatives 1, 3 and 6 are stabilized by the σC3-S4→σ* C2-N5 orbital interaction (though bond coupling) along with the LPO1→σ*S4-C10 interaction for 6. The gauche preference may be ascribed to the stabilizing orbital interactions in the gauche conformers and also to the destabilization of the cis conformer due to the electrostatic repulsion between Cδ+‒Sδ- and Cδ+=Oδ- dipoles. This Repulsive Field Effect is also responsible for the higher νCO frequency of the cis conformer with respect to that of the gauche conformer in the whole series. X ray single crystal analysis of 4 indicates that this compound adopts in the solid the cis2 conformation obtained in the gas phase for compound 6. In order to obtain the largest energy gain the molecules are arranged in the crystal by six molecules synthons mediated by C-H…O and Cl…Cl interactions. The geometry of this last interaction is called Type I, as the chlorine atoms are related by a crystallographic inversion center.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
