The analysis of the IR νCO bands of the 2-ethylsulfinyl-(4'-substituted)-phenylthioacetates 4’-Y-C6H4SC(O)CH2S(O)Et (Y = NO2 1, Cl 2, Br 3, H 4, Me 5, OMe 6) supported by B3LYP/6-31G(d,p) calculations along with the NBO analysis for 1, 4 and 6 and X-ray analysis for 3, indicated the existence of four gauche (q-g-syn, g3-syn, g1-anti and q-g2-syn) conformers for 1–6. The calculations reproduce quite well the experimental results, i.e. the computed q-g-syn and g3-syn conformers correspond in the IR spectrum (in solution), to the νCO doublet higher frequency component of larger intensity, while the computed g1-anti conformer correspond to the νCO doublet lower frequency component (in solution). NBO analysis showed that the nS→π*C1-O2, nO(CO)→σ*C1-S3, nO(CO)→σ*C1-C4 orbital interactions are the main factors which stabilize the q-g-syn, g3-syn, g1-anti and q-g2-syn conformers for 1, 4 and 6. The nO(CO)→σ*C1-S3 interaction which stabilizes the q-g-syn, g3-syn and q-g2-syn conformers into a larger extent than the g1-anti conformer, is responsible for the larger νCO frequencies of the former conformers relative to the latter one. The q-g-syn, g3-syn and q-g2-syn conformers are further stabilized by σC4-S5→π*CO (strong), π*CO /σ∗C4-S5, nO(CO)→σ*C6-H17[Et] (weak) and π*CO /σ∗C4-S5 (strong) orbital interactions. The g1-anti conformer is also stabilized by σC4-S5→π*CO (strong), πCO /σ∗C4-S5, nO(CO)→σ*C6-H17[Et], πC9=C11[Ph] →σ∗C4-H16[α-CH2] (weak), nO(SO)→σ*C11-H23[o-Ph] (medium) and π*CO /σ∗C4-S5 (strong) orbital interactions. The q-g-syn conformeris further stabilized by Oδ−(CO)…Sδ+(SO) attractive Coulombic interaction while the q-g2-syn conformer is destabilized by the nS5…Oδ−(CO) repulsive Coulombic interaction. This analysis indicates the following conformer stabilization order: q-g-syn; g3-syn > g1-anti q-g2-syn. X-ray single crystal analysis of 3 indicates that it assumes in the solid a distorted q-g2-syn geometry which is stabilized through almost the same orbital and Coulombic interaction which takes place for the q-g2-syn conformer, in the gas, along with dipole moment coupling and a series intermolecular C-H…O interactions.
Spectroscopic and theoretical studies of some 2-ethylsulfinyl-(4'-substituted)-phenylthioacetates
DAL COLLE, Maurizio
2010
Abstract
The analysis of the IR νCO bands of the 2-ethylsulfinyl-(4'-substituted)-phenylthioacetates 4’-Y-C6H4SC(O)CH2S(O)Et (Y = NO2 1, Cl 2, Br 3, H 4, Me 5, OMe 6) supported by B3LYP/6-31G(d,p) calculations along with the NBO analysis for 1, 4 and 6 and X-ray analysis for 3, indicated the existence of four gauche (q-g-syn, g3-syn, g1-anti and q-g2-syn) conformers for 1–6. The calculations reproduce quite well the experimental results, i.e. the computed q-g-syn and g3-syn conformers correspond in the IR spectrum (in solution), to the νCO doublet higher frequency component of larger intensity, while the computed g1-anti conformer correspond to the νCO doublet lower frequency component (in solution). NBO analysis showed that the nS→π*C1-O2, nO(CO)→σ*C1-S3, nO(CO)→σ*C1-C4 orbital interactions are the main factors which stabilize the q-g-syn, g3-syn, g1-anti and q-g2-syn conformers for 1, 4 and 6. The nO(CO)→σ*C1-S3 interaction which stabilizes the q-g-syn, g3-syn and q-g2-syn conformers into a larger extent than the g1-anti conformer, is responsible for the larger νCO frequencies of the former conformers relative to the latter one. The q-g-syn, g3-syn and q-g2-syn conformers are further stabilized by σC4-S5→π*CO (strong), π*CO /σ∗C4-S5, nO(CO)→σ*C6-H17[Et] (weak) and π*CO /σ∗C4-S5 (strong) orbital interactions. The g1-anti conformer is also stabilized by σC4-S5→π*CO (strong), πCO /σ∗C4-S5, nO(CO)→σ*C6-H17[Et], πC9=C11[Ph] →σ∗C4-H16[α-CH2] (weak), nO(SO)→σ*C11-H23[o-Ph] (medium) and π*CO /σ∗C4-S5 (strong) orbital interactions. The q-g-syn conformeris further stabilized by Oδ−(CO)…Sδ+(SO) attractive Coulombic interaction while the q-g2-syn conformer is destabilized by the nS5…Oδ−(CO) repulsive Coulombic interaction. This analysis indicates the following conformer stabilization order: q-g-syn; g3-syn > g1-anti q-g2-syn. X-ray single crystal analysis of 3 indicates that it assumes in the solid a distorted q-g2-syn geometry which is stabilized through almost the same orbital and Coulombic interaction which takes place for the q-g2-syn conformer, in the gas, along with dipole moment coupling and a series intermolecular C-H…O interactions.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
