Vicinal proton−proton NMR couplings have been employed to estimate the differences in conformational
equilibria for 1,4-butanedioic-2,3-13C2 acid in the progression of its diprotic to monoprotic to di-ionized forms
as a function of solvent in water and in a series of alcohols ranging from methanol to tert-butyl alcohol.
Except for water, the percentage of gauche increases from diacid to monoanion and then decreases from
monoanion to dianion. The substantial gauche preference for the monoanion species in the less-polar alcohols
is clearly the result of intramolecular hydrogen bonding.
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