Structural characterization of stearic acid in the crystalline state by the cross polarization in solid state 13C NMR

C-13 cross polarization/magic angle spinning (CP/MAS) NMR spectra of stearic acid with the crystallographic form C, deuterated the methyl and methylene groups besides a proton in the carboxylic group, were measured as a function of the contact time, in order to obtain the cross relaxation rate (1/T-CH) between the methylene carbons and protons in the compound. From these experimental results, it was found that the 1/T-CH values for the methylene carbons are proportional to r(av)(-6), which is the averaged atomic distance between any specified carbon and protons. This means that the CP experiment provides a geometrical information using the partially deuterated molecules. (C) 1999 Elsevier Science B.V. All rights reserved.