The infrared active CD2rocking vibration of selectively deuterated palmitic and stearic acids is used as a probe for the mapping of the local conformation of these molecules in the solid and liquid phases. The infrared spectra at different temperatures are analyzed and interpreted by means of normal coordinate calculations and conformational energy calculations. Evidence is collected that in theCsolid modification molecules are fullytransplanar. The cooperatively distorted local conformation of the carboxyl group in the liquid phase is discussed.
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