Conformations and barriers to inversion of seven-membered cyclic oxamides and their monothio- and dithio-analogues: a study by dynamic nuclear magnetic resonance spectroscopy and molecular mechanics
- 1 January 1981
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 10,p. 1344-1350
- https://doi.org/10.1039/p29810001344
Abstract
Conformations and barriers to inversion of NN′-dialkylperhydrodiazepine-2,3-dione and its monothio- and dithio-analogues have been studied by 1H n.m.r. spectroscopy and by molecular mechanics calculations. Experiments as well as calculations indicate that the compounds studied adopt a twist-boat conformation (C2 symmetry). The inversion of the ring system involves a passage through a Cs structure with a planar s-cis-(thio)oxamide unit. The free energy barriers increase in the order oxamide < monothio-oxamide < dithio-oxamide. The calculations indicate that the dominant part of the barrier is of steric origin; the electrostatic contribution is <20% of the total barrier height.Keywords
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