| Автор | Lomas, John S. |
| Автор | Adenier, Alain |
| Дата выпуска | 2002 |
| dc.description | Di-1-adamantyl and (1-adamantyl)(tert-butyl) analogues are compared with the previously studied 3- or 3- and 4-substituted 2-thienyl(di-tert-butyl)methanols. The equilibrium constants for synâ anti rotamerization ([syn]/[anti]) are slightly greater than for the smaller di-tert-butyl derivatives. In the intramolecularly hydrogen-bonded anti rotamers, neither the <sup>1</sup>H NMR shift of the hydroxy proton nor the OH stretching frequency, both indicators of intramolecular hydrogen bond strength, is greatly affected by a change in the tert-alkyl group; these changes in the equilibrium constants must, therefore, be attributed to variations in steric effects. The rotation barriers for the compounds with the larger tert-alkyl groups are much enhanced and better differentiated. In all three sets the synâ anti and antiâ syn rotation barriers are linearly correlated, and either can be correlated with the free energy difference. Nevertheless, the data do not meet the criteria for a classical Lefflerâ Grunwald-type rate-equilibrium relationship. Molecular mechanics calculations (MMFF94 force field) account fairly well for the variation in the free energy difference for rotamer pairs of the di-1-adamantyl, (1-adamantyl)(tert-butyl) and di-tert-butyl derivatives, but slightly overestimate the small differences in the equilibrium constants for the three series. The calculated rotation barriers for the di-tert-butyl compounds are about 7 kcal mol<sup>â 1</sup> higher than those observed. Those for 2-anisyl-, phenyl- and 2-tolyldialkylmethanols are increasingly overestimated as the rotation barrier rises, but a good correlation ranging over 20 kcal mol<sup>â 1</sup> is obtained; this correlation is not coincident with that for the thiophene derivatives. |
| Формат | application.pdf |
| Издатель | Royal Society of Chemistry |
| Название | Rate and equilibrium effects of tert-alkyl groups on rotamerization in 3,4-alkylenedioxy-, 3-alkoxy- and 3,4-dialkoxy-2-thienyl(di-tert-alkyl)methanols: an IR, NMR, kinetics and MM studyElectronic supplementary information (ESI) available: additional experimental data. See http://www.rsc.org/suppdata/p2/b2/b203714a/ |
| Тип | research-article |
| DOI | 10.1039/b203714a |
| Electronic ISSN | 1364-5471 |
| Print ISSN | 0300-9580 |
| Журнал | Journal of the Chemical Society, Perkin Transactions 2 |
| Первая страница | 1264 |
| Последняя страница | 1270 |
| Аффилиация | Lomas John S.; ITODYS, Université de Paris 7 |
| Аффилиация | Adenier Alain; ITODYS, Université de Paris 7 |
| Выпуск | 7 |
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