ISSN:
0749-1581
Keywords:
Cis-trans isomerism
;
Keto-enol tautomerism
;
1H and 13C NMR
;
N-Methylhydroxamic acids
;
O-Methylhydroxamic acids
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
1H and 13C NMR studies of N-methyl-substituted hydroxamic acids, RCON(CH3)OH (R = CH3, C2H5 and C6H5), show that the series exhibits cis-trans isomerism about the C—N bond. The Z/E ratio increases in the series CH3 〈 C2H5 〈 n-C5H11 〈 n-C6H13 for a given solvent, indicating that steric interaction between R and the OH group is more important than that between R and the CH3 group. In DMSO-d6 the Z isomer is preferentially stabilized by solvation, whereas in C6D6 and toluene-d8 the unsolvated E form is thermodynamically more stable, as predicted by ab initio molecular orbital calculations. (12) At high concentrations (in CDCl3, CD2Cl2, C6D6 and toluene-d8) the E isomer may also be stabilized by intermolecular association. In the O-methyl-substituted series, RCONHOCH3 (R = CH3, C6H5), although the Z isomer predominates in all solvents, at low temperatures there is evidence for enolic forms.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260290109
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