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Updated: Jun 22, 2026

Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
Published on: July 27, 2022
Dynamic (1)H NMR spectroscopic study of the ring inversion in N-sulfonyl morpholines--studies on N-S interactions
Ali Reza Modarresi-Alam1, Homeyra Alsadat Amirazizi, Hajar Bagheri
1Department of Chemistry, Faculty of Science, University of Sistan & Baluchestan, Zahedan, Iran. modaresi@chem.usb.ac.ir
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.
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