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Conformational Behaviour of Medium-sized Rings. Part 10. Dithiosalicylides and Trithiosalicylides

DOI: 10.1039/P19820001637

Source and publish data:

Journal of the Chemical Society. Perkin transactions I p. 1637 - 1648 (1982)

Update date:2022-08-05

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Authors:

Guise, G. BruceGuise, G. Bruce

Ollis, W. DavidOllis, W. David

Peacock, Judith A.Peacock, Judith A.

Stephanatou, Julia StephanidouStephanatou, Julia Stephanidou

Stoddart, J. FraserStoddart, J. Fraser

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Article abstract of DOI:10.1039/P19820001637

The trithiosalicylide derivatives (8)-(11) have been synthesised and shown by temperature-dependent 1H n.m.r. spectroscopy to exist in solution as ring inverting (35a)<*>(35b) enantiomeric helical conformations with trans-thioester linkages.The free energies of activation for these conformational changes are ca. 10 kcal mol-1 higher than those for the similar process in the corresponding trisalicylides.In contrast with the trisalicylides, the trithiosalicylides can only ring invert between enantiomeric helical conformations via intermediates containing a cis-thioester linkage.The dithiosalicylide derivatives (3)-(7) have been synthesised; the temperature dependence of the 1H n.m.r. spectrum of di-o-thiothymotide (7) has been interpreted in terms of ring inversion (40a)<*>(40b) between enantiomeric boat conformations.Comparison of the ΔG<*> value of 24.6 kcal mol-1 for this conformational change with that of 17.7 kcal mol-1 previously obtained for di-o-thymotide (41) suggests that cis-thioester linkages are subject to more resonance stabilisation than are cis-ester linkages.

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