Stereochemical and electronic interaction studies of some N-methoxy- N-methyl-2-[(4′-substituted)phenylsulfinyl]propanamides

• Published in: Journal of molecular structure Vol. 892; no. 1; pp. 360 - 372
• Main Authors: Olivato, Paulo R., Domingues, Nelson L.C., Mondino, Mirta G., Lima, Filipe S., Zukerman-Schpector, Julio, Rittner, Roberto, Colle, Maurizio Dal
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-12-2008
• Subjects: Infrared spectroscopy; N-methoxy- N-methyl-2-[(4′-substituted)phenylsulfinyl]propanamides; Stereochemical isomerism; Theoretical calculations; X-ray diffraction analysis; N-methoxy- N-methyl-2-[(4′-substituted)phenylsulfinyl]propanamides; Infrared spectroscopy; Theoretical calculations; X-ray diffraction analysis; Stereochemical isomerism
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2008.06.003

The
1H NMR spectra of
N-methoxy-
N-methyl-2-[(4′-substituted)phenylsulfinyl]-propanamides [Y-Ph-S(O)CH(Me)C(O)N(OMe)Me; Y
=
OMe
1, Me
2, H
3, Cl
4, NO
2
5] along with the X-ray diffraction analysis of the nitro-derivative (
5), have shown the existence of two pairs of diastereomers (racemic mixture) [C
RS
S/C
SS
R (
diast
1) and C
RS
R/C
SS
S (
diast
2)] in the ratio of
ca. 7:3, respectively. The
ν
CO IR analysis of the title compounds supported by HF and B3LYP/6-31G∗∗ calculations of
3 and of the parent
N-methoxy-
N-methyl-propanamide (
6) by HF, have shown that
diast
1 exists in an equilibrium between the two more polar and more stable
quasi-cis (
q-c
1
and
q-c
2
) conformers and the
gauche(g) conformer. The population of the
g conformer in the equilibrium increases with the increase in the solvent polarity, which is attributed to a larger solvation effect on the carbonyl and sulfinyl groups.
Diast
2 of compound
3 occurs in the gas phase as an equilibrium between the most stable
quasi-gauche (q-g) conformer and the
quasi-cis (q-c) conformer, both presenting very similar dipole moments. The former is stabilized by electrostatic and charge transfer interactions, which results in a less solvated spatial arrangement. Moreover, all conformers of both diastereomers are stabilized by several intramolecular hydrogen bonds. X-ray single crystal analysis performed for
diast
1 and for
diast
2 of
5 indicates that both stereoisomers assume, in the solid state, the
anti-clinal (
gauche) conformation. For the crystal packing,
diast
1 of
5 is made up of three molecules joined through two centro-symmetric H...O hydrogen bonds.