title: Dynamic (1)H NMR spectroscopic study of the ring inversion in N-sulfonyl morpholines--studies on N-S interactions.
abstract: The effect of the exocyclic conjugation, via d-p orbital interaction and/or negative hyperconjugation (anomeric effect) of the N-S bond, on the inversion of the morpholine ring in some N-arylsulfonyl morpholines is studied by variable-temperature (1)H NMR spectroscopy in different solvents. The observed free energy barriers are 9.2-10.3 kcal mol(-1); the lower values were obtained with increasing conjugation (substituents of higher electron withdrawing power) along the series. The barrier to ring inversion of 1e was solvent independent. X-ray data of compounds 1b,d reveal the chair conformation of the six-membered ring, the flattened pyramidal orientation of the ring nitrogen atom, and the sulfonyl group in equatorial position with the plane containing the C(aryl)-S-N bond perpendicular to the plane of the benzene ring. In addition, the sulfonamide group prefers a conformation with the S-C bond antiperiplanar with respect to the nitrogen atom lone pair and the -CH(2)-N-CH(2)- moieties in staggered conformation with the S-O bonds of the SO(2) group.
authors: Department of Chemistry, Faculty of Science, University of Sistan & Baluchestan, Zahedan, Iran. modaresi@chem.usb.ac.ir
authors: Ali Reza
authors: AR
authors: Modarresi-Alam
authors: Homeyra Alsadat
authors: HA
authors: Amirazizi
authors: Hajar
authors: H
authors: Bagheri
authors: Hamid-Reza
authors: HR
authors: Bijanzadeh
authors: Erich
authors: E
authors: Kleinpeter
mesh_terms: D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D015394:Molecular Structure; D009025:Morpholines / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000737:chemistry*
chemical_list: D009025:Morpholines; D013449:Sulfonamides