A 13C NMR spectroscopic study of the phase transitions of alkane dicarboxylic acids in the solid state

13C NMR spectra of a few odd-member alkane dicarboxylic acids such as glutaric and pimelic acids have been studied across their phase transitions. The spectra provide clear evidence for the structural changes accompanying the transitions. In the case of malonic acid, the study establishes that the two carboxyl units are equivalent in the high-temperature phase unlike in the other odd-member dicarboxylic acids where they are non-equivalent.