endo-Anomeric and exo-anomeric effects in 2-substituted tetrahydropyrans
- 1 January 1985
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Chemical Communications
- No. 8,p. 467-468
- https://doi.org/10.1039/c39850000467
Abstract
Determinations by variable temperature 13C and/or 1H n.m.r spectroscopy of equilibrium constants for inversion of 2-substituted tetrahydropyrans and comparisons with substituted cyclohexanes have given ‘anomeric effects (ΔΔH°)’ of +2.12, +0.75, +0.61, and –0.33 kcal mol–1(1 cal = 4.184 J) for substituents Cl, OMe, OH, and NHMe respectively; this sequence confirms the importance of antiperiplanar n-σ* stabilisation but supports the suggestion that endo-anomeric and exo-anomeric effects which occur in the same conformation are competitive.Keywords
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