Conformational studies by dynamic nuclear magnetic resonance. Part 30. Exchange kinetics between the rotamers of 2-acyl-furans and -thiophenes
- 1 January 1985
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 11,p. 1839-1844
- https://doi.org/10.1039/p29850001839
Abstract
Low-temperature 13C n.m.r. spectra allowed the observation of two different groups of signals, corresponding to the O,O-anti- and O,O-syn-rotamers, of a number of 2-acylfurans with the following alkyl groups bonded to carbonyl: Me, Et, Pri, But, pentan-3-yl. The ratios of these rotamers in dimethyl ether were thus obtained, and the barriers for the syn-anti interconversion were found to decrease with increasing bulkiness of the alkyl groups. Although separate 13C signals could not be detected for the rotamers of the corresponding 2-acylthiophenes, line-broadening effects nonetheless allowed measurement of the interconversion barriers. Lanthanide-induced shift experiments carried out on the latter derivatives (at both 1H and 13C frequencies) showed that in all the 2-acylthiophenes investigated the S,O-syn rotamers are predominant.Keywords
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