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Carbon-13 spin–lattice relaxation in strongly associated molecules: Carboxylic acids

✍ Scribed by George C. Levy; Dan Terpstra

Publisher
John Wiley and Sons
Year
1976
Tongue
English
Weight
279 KB
Volume
8
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

^13^C spin–lattice relaxation times determined for the protonated carbons of carboxylic acids and methyl esters give indications of solution dimerization with the free acids. Since isopthalic and fumaric acids have two carboxyl functions they are able to polymerize in solution. Unlike the case for molecular aggregation due to weak hydrogen bonding in solution (e.g. alcohols, phenols), the ^13^C T~1~ values of mono carboxylic acids are not significantly affected by dilution to c. 10^−2^ M. Variable temperature T~1~ measurements of both the mono and dibasic acids gave activation energies for molecular reorientation of the order of 2 kcal mol^−1^, considerably lower than E~a~ for hydrogen bonded alcohols and comparable with E~a~ for the unassociated methyl esters of propionic and benzoic acids.

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