The analysis of the IR carbonyl band of the N-methoxy-N-methyl-2-[(4’-substituted)phenylthio]propanamides Y-PhSCH(Me)C(O)N(OMe)Me (Y=OMe 1, Me 2, H 3, Cl 4, NO2 5), supported by B3LYP/cc-pVDZ calculations of 3, indicated the existence of two gauche conformers (g1 and g2), the g1 conformer being the more stable and the less polar one (in gas phase and in solution). Both conformers are present in solution of the polar solvents (CH2Cl2 and CH3CN) for 1-5 and in solution of the less polar solvent (CHCl3) for 1-4, while only the g1 conformer is present in solution of non polar solvents (n-C6H14 and CCl4) and in solution of CHCl3 for 5. NBO analysis shows that both the σC-S→ π*C=O (hyperconjugative) and the πC=O→ σ*C-S orbital interactions contribute almost to the same extent for the stabilization of g1 and g2 conformers. The π*C=O→ σ*C-S, nS→ π*C=O and the nS→ π*C=O orbital interactions stabilize more the g1 conformer than the g2 one. Moreover, the suitable geometry of the g1 conformer leads to its stabilization through the LPO2→ σ*C8-H11 orbital interaction (hydrogen bond) along with the strong Oδ-[CO]....Hδ+[o-Ph] electrostatic interaction. On the other hand, the appropriate geometry of the g2 conformer leads to its stabilization by the LPO22→ σ*C9-H13 orbital interaction (hydrogen bond) along with the weak Oδ-[OMe].... Hδ+[o’-Ph] electrostatic interaction. As for the 4’-nitro derivative 5 the ortho-phenyl hydrogen atom becomes more acidic, leading to a stronger Oδ-[CO].... Hδ+[o-Ph] interaction and, thus, into a larger stabilization of the g1 conformer in the whole series. This trend is responsible for the unique IR carbonyl band in CHCl3 solution of 5. The larger occupancy of the π*C=O orbital of the g1 conformer relative to that of the g2 conformer, along with the Oδ-[CO].... Hδ+[o-Ph] electrostatic interaction (hydrogen bond) justifies the lower carbonyl frequency of the g1conformer with respect to the g2 one, in gas phase and in solution.

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

DAL COLLE, Maurizio
2009

Abstract

The analysis of the IR carbonyl band of the N-methoxy-N-methyl-2-[(4’-substituted)phenylthio]propanamides Y-PhSCH(Me)C(O)N(OMe)Me (Y=OMe 1, Me 2, H 3, Cl 4, NO2 5), supported by B3LYP/cc-pVDZ calculations of 3, indicated the existence of two gauche conformers (g1 and g2), the g1 conformer being the more stable and the less polar one (in gas phase and in solution). Both conformers are present in solution of the polar solvents (CH2Cl2 and CH3CN) for 1-5 and in solution of the less polar solvent (CHCl3) for 1-4, while only the g1 conformer is present in solution of non polar solvents (n-C6H14 and CCl4) and in solution of CHCl3 for 5. NBO analysis shows that both the σC-S→ π*C=O (hyperconjugative) and the πC=O→ σ*C-S orbital interactions contribute almost to the same extent for the stabilization of g1 and g2 conformers. The π*C=O→ σ*C-S, nS→ π*C=O and the nS→ π*C=O orbital interactions stabilize more the g1 conformer than the g2 one. Moreover, the suitable geometry of the g1 conformer leads to its stabilization through the LPO2→ σ*C8-H11 orbital interaction (hydrogen bond) along with the strong Oδ-[CO]....Hδ+[o-Ph] electrostatic interaction. On the other hand, the appropriate geometry of the g2 conformer leads to its stabilization by the LPO22→ σ*C9-H13 orbital interaction (hydrogen bond) along with the weak Oδ-[OMe].... Hδ+[o’-Ph] electrostatic interaction. As for the 4’-nitro derivative 5 the ortho-phenyl hydrogen atom becomes more acidic, leading to a stronger Oδ-[CO].... Hδ+[o-Ph] interaction and, thus, into a larger stabilization of the g1 conformer in the whole series. This trend is responsible for the unique IR carbonyl band in CHCl3 solution of 5. The larger occupancy of the π*C=O orbital of the g1 conformer relative to that of the g2 conformer, along with the Oδ-[CO].... Hδ+[o-Ph] electrostatic interaction (hydrogen bond) justifies the lower carbonyl frequency of the g1conformer with respect to the g2 one, in gas phase and in solution.
2009
Paulo R., Olivato; Nelson L. C., Domingues; Mirta G., Mondino; Cláudio F., Tormena; Roberto, Rittner; DAL COLLE, Maurizio
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/530616
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 15
  • ???jsp.display-item.citation.isi??? 13
social impact