Dynamic 1H NMR spectroscopic study of the ring inversion in N-sulfonyl morpholines-studies on N-S interactions
- 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 1H 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 Caryl;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 ;CH2;N;CH2; moieties in staggered conformation with the S;O bonds of the SO2The 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 1H 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 Caryl;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 ;CH2;N;CH2; moieties in staggered conformation with the S;O bonds of the SO2 group.…
Author details: | Ali Reza Modarresi-Alam, Homeyra Alsadat Amirazizi, Hajar Bagheri, Hamid-Reza Bijanzadeh, Erich KleinpeterORCiDGND |
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ISSN: | 0022-3263 |
Publication type: | Article |
Language: | English |
Year of first publication: | 2009 |
Publication year: | 2009 |
Release date: | 2017/03/25 |
Source: | Journal of organic chemistry. - ISSN 0022-3263. - e-ISSN 1520-6904. - 74 (2009), 13, S. 4740 - 4746 |
Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie |
Peer review: | Referiert |