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1H and 13C N.M.R. Studies on the Positional Isomers of Methyl Thialaurate and Methyl Thiastearate
Jie, Marcel S. F. Lie Ken,Bakare, Oladapo
, p. 2121 - 2126 (2007/10/02)
1H N.m.r. analysis of methyl thialaurate and methyl thiastearate shows that the sulphur atom in the alkyl chain has a significant deshilding effect (α-effect) on the chemical shift of the protons of the adjacent methylene and methyl groups, and also on the methyl protons of the methoxycarbonyl (ester) function.It was possible to identify seven of the positional isomers in each series by examining the chemical shifts and the splitting pattern of the signals in the 1H n.m.r. spectra of these fatty acid ester analogues.The 13C n.m.r. results showed that this S atom has an interesting effect (α-, β-, and γ-effect) on the chemical shift of the carbonyl carbon atom of the methoxycarbonyl (ester) function: the sulphur atom exerts a significant shilding effect in the case of the 2-, 3-, and 4-thia isomers.In the remaining isomers the sulphur atom causes a strong deshilding effect on the methylene or methyl carbon atoms on either side of the sulphide linkage.These results permitted all positional isomers of methyl thialaurate to be identified by this technique, while 10 out of the 16 positional isomers of methyl thiastearate could be characterized.
