The analysis of the IR carbonyl band of the N-methoxy-N-methyl-2-[(4’-substituted)phenylsulfonyl]propanamides Y-PhSCH(Me)C(O)N(OMe)Me (Y=OMe 1, Me 2, H 3, Cl 4, NO2 5), supported by HF/6-31G(d,p) calculations of 3, indicated the existence of two gauche conformers (g1 and g2), being the g1 conformer the most stable and the least polar one (in gas phase and in solution). Both conformers are present in solution of the non polar solvent (CCl4) for 1-5 and in solution of the more polar solvents (CHCl3 ) for 1, 4, 5 and (CH2Cl2) for 5, while only the g1 conformer is present in solution of the most polar solvent (CH3CN) for 1-5. The g1 and g2 conformers correspond to the racemic mixture of diastereomers (diast1 and diast2 ) whose relative configurations are [C(3)RNR]/ [C(3)SNS] and [C(3)RNS]/ [C(3)SNR], respectively. The computed carbonyl frequencies for g1 (diast1) and g2 (diast2) stereoisomers of 3 matches well the values the experimental values. In fact the νCO frequencies for g1 (1669 cm-1) and g2 (1681 cm-1) in gas phase corresponds to the more intense lower less intense and higher doublet νCO frequency components, respectively, in solution of the non polar solvent CCl4 (fundamental and first overtone) for compounds 1-5. The NBO analysis shows that the most important orbital interaction for 3 is the nN → π*CO interaction which corresponds to the [O-C=N ↔ -O-C=N+] conjugation, being the delocalization energy for the g1 conformer larger than that for the g2 conformer The following orbital interactions stabilize the g1 conformer into a large extent than the g2 one: LPO11(SO2)→σ*C19-H20 (OMe); LPO1(CO)→σ*C23-H26 (NMe), π*C2=O1 →σ*C3-S4. On the other hand the g2 conformer is stabilized into a larger extent than the g1 one: LPO11(SO2)→σ*C3-S4; LPO11(SO2)→σ*S4-C5; σC3-S4→π*C2=O1; πC2=O1→σ*C3-S4. Therefore the overall balance of the orbital interaction for both conformers (g1 and g2) conformers indicates that the g1 conformer is more stable than the g2 one, which in turn is in good agreement with the theoretical and experimental data from which the g1 conformer is more stable than the g2 one.The abnormal solvent effect observed on the relative intensities of the carbonyl doublet components, is due to the closeness between the sulfonyl oxygen (O11) and the methoxyl oxygen (O18) atoms of the g2 conformer (diast2) which hinders the solvation of these atoms with respect to the same atoms of the g1 conformer (diast1). X-ray single crystal analysis performed for 3 shows the existence of two g2a and g1b conformers of diastereomers (diast2a and diast1b) whose absolute configurations are [C(3)RNS] and [C(3)RNR], respectively. Contrarily to the gas state, in the crystal. the more polar g2a conformer is the more stable and the less polar g1b conformer is the less populated The larger stabilization of the g2a conformer over the g1b form in the crystals may be associated with a larger energy gain deriving from dipole moment coupling in the former conformer along with a series of C-H…O electrostatic and hydrogen bond interactions

Spectroscopic and theoretical studies of some N-methoxy-N-methyl-2-[(4´-substituted) phenylsulfonyl]propanamides

DAL COLLE, Maurizio
2009

Abstract

The analysis of the IR carbonyl band of the N-methoxy-N-methyl-2-[(4’-substituted)phenylsulfonyl]propanamides Y-PhSCH(Me)C(O)N(OMe)Me (Y=OMe 1, Me 2, H 3, Cl 4, NO2 5), supported by HF/6-31G(d,p) calculations of 3, indicated the existence of two gauche conformers (g1 and g2), being the g1 conformer the most stable and the least polar one (in gas phase and in solution). Both conformers are present in solution of the non polar solvent (CCl4) for 1-5 and in solution of the more polar solvents (CHCl3 ) for 1, 4, 5 and (CH2Cl2) for 5, while only the g1 conformer is present in solution of the most polar solvent (CH3CN) for 1-5. The g1 and g2 conformers correspond to the racemic mixture of diastereomers (diast1 and diast2 ) whose relative configurations are [C(3)RNR]/ [C(3)SNS] and [C(3)RNS]/ [C(3)SNR], respectively. The computed carbonyl frequencies for g1 (diast1) and g2 (diast2) stereoisomers of 3 matches well the values the experimental values. In fact the νCO frequencies for g1 (1669 cm-1) and g2 (1681 cm-1) in gas phase corresponds to the more intense lower less intense and higher doublet νCO frequency components, respectively, in solution of the non polar solvent CCl4 (fundamental and first overtone) for compounds 1-5. The NBO analysis shows that the most important orbital interaction for 3 is the nN → π*CO interaction which corresponds to the [O-C=N ↔ -O-C=N+] conjugation, being the delocalization energy for the g1 conformer larger than that for the g2 conformer The following orbital interactions stabilize the g1 conformer into a large extent than the g2 one: LPO11(SO2)→σ*C19-H20 (OMe); LPO1(CO)→σ*C23-H26 (NMe), π*C2=O1 →σ*C3-S4. On the other hand the g2 conformer is stabilized into a larger extent than the g1 one: LPO11(SO2)→σ*C3-S4; LPO11(SO2)→σ*S4-C5; σC3-S4→π*C2=O1; πC2=O1→σ*C3-S4. Therefore the overall balance of the orbital interaction for both conformers (g1 and g2) conformers indicates that the g1 conformer is more stable than the g2 one, which in turn is in good agreement with the theoretical and experimental data from which the g1 conformer is more stable than the g2 one.The abnormal solvent effect observed on the relative intensities of the carbonyl doublet components, is due to the closeness between the sulfonyl oxygen (O11) and the methoxyl oxygen (O18) atoms of the g2 conformer (diast2) which hinders the solvation of these atoms with respect to the same atoms of the g1 conformer (diast1). X-ray single crystal analysis performed for 3 shows the existence of two g2a and g1b conformers of diastereomers (diast2a and diast1b) whose absolute configurations are [C(3)RNS] and [C(3)RNR], respectively. Contrarily to the gas state, in the crystal. the more polar g2a conformer is the more stable and the less polar g1b conformer is the less populated The larger stabilization of the g2a conformer over the g1b form in the crystals may be associated with a larger energy gain deriving from dipole moment coupling in the former conformer along with a series of C-H…O electrostatic and hydrogen bond interactions
2009
Paulo R., Olivato; Nelson L. C., Domingues; Adriana K. C. A., Reis; Elisângela, Vinhato; Mirta G., Mondino; Julio Zukerman, Schpector; Roberto, Rittner; DAL COLLE, Maurizio
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1377557
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