Premium
13 C nuclear magnetic resonance studies of saturated heterocycles: II —substituent effects on the 13 C chemical shifts of methyl substituted 1,3‐dithianes and their application to the determination of conformational equilibria
Author(s) -
Pihlaja Kalevi,
Björkqvist Börje
Publication year - 1977
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270090909
Subject(s) - substituent , chemical shift , chemistry , conformational isomerism , cyclohexane , dithiane , resonance (particle physics) , computational chemistry , stereochemistry , molecule , organic chemistry , physics , particle physics
The 13 C chemical shifts for 1,3‐dithiane and 9 methyl substituted derivatives are reported. Only three of the methyl‐1,3‐dithianes were conformationally anancomeric and hence the conformational equilibria must be taken into account when deriving the values of the different substituent effects on the 13 C chemical shifts. The best fit for each substituent effect was obtained when –Δ G θ (5 a ‐Me) for 5‐methyl‐1,3‐dithiane was given the value 3.8 ± 0.3 kJ mol −1 and when the difference between –Δ G θ (2 a ‐Me) and –Δ G θ (5 a ‐Me) for cis ‐2,5‐dimethyl 1,3‐dithiane equalled 3.4 ± 0.4 kJ mol −1 . The conformer populations chosen from our earlier paper 1 were then suitable for all the other conformational equilibria in question. The magnitude of the derived substituent effects are compared with those for cyclohexane and 1,3‐dioxane.