On the chirality of 2-hydroxy-NN-dialkythiobenzamides. Demonstration of three consecutive conformational processes
- 1 January 1980
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 7,p. 949-956
- https://doi.org/10.1039/p29800000949
Abstract
The geminal anisochronism observed in the 1H n.m.r. spectra of some of the title compounds has previously been ascribed to different causes. It has now been unequivocally shown that the geminal anisochronism is a consequence of the molecular chirality arising from slow rotation of the aryl ring with respect to the thioamide group. The free-energy barrier to this process has been found to lie in the range 11.2–13.4 kcal mol–1, increasing with the size of the N-alkyl groups. A lower energy process (ΔG‡= 8.6 kcal mol–1) in 2-hydroxy-NN-di-isobutylthiobenzamide has been identified as the exchage of the isobutyl groups between two anti-periplanar positions. The third process with the highest barrier in each case (ΔG‡= 13.4–15.6 kcal mol–1) is the E–Z exchange of the alkyl groups by rotation around the C(S)–N bond.Keywords
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