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Markham GD, Bock CW
The interaction of water with sulfonium ions and the effects of hydration on the energetics of methyl group transfer: An ab initio molecular orbital study of the hydration of (CH3)(3) S+ and (CH3)(2) S+CH2CO2
Structural Chemistry (1996) 7:281-300.
Abstract
The interactions of the sulfonium ions (CH3S+ (CH3)(2)S+CH2CO2- , and (CH3S+- CH2CH2CO2- with up to four water molecules have been studied by ab initio molecular orbital methods. Complexes of (CH3S+ with one to three water molecules involve strong electrostatic sulfur-oxygen interactions; in contrast, the sulfide (CH3)(2)S interacts with water molecules via weak S-H hydrogen bonds, suggesting that methyl-group transfer from (CH3S+ in aqueous solution involves a significant alteration of the hydration pattern around the sulfur atom. Two conformers of (CH3)(2)S+CH2CO2- were found that display sulfur-oxygen distances which are approximately 0.3 Angstrom less than the sum of the sulfur and oxygen van der Waals radii, indicating a strong intramolecular electrostatic interaction. For the complexes (CH3)(2)S+CH2CO2- . nH(2)O (n = 1-4), water interacts primarily with the carboxylate group via hydrogen bonds, rather than electrostatically with the sulfur atom, although in complexes with the three- and four-water complexes, the proximity of the positively charged sulfur atom to the carboxylate group significantly alters the hydration pattern compared to that in the corresponding of complexes CH3SCH2CO2-. Thus, methyl transfer from (CH3)(2)S+CH2CO2- to an acceptor in aqueous solution also involves substantial changes in the hydration pattern around the carboxylate group.
Note
Publication Date: 1996-08-01.
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