A deuteron magnetic resonance study of a single crystal of deuterated malonic acid

Abstract

A single crystal of deuterated malonic acid has been studied at room temperature by deuteron magnetic resonance (DMR). An analysis of the results yielded four electric quadrupole interaction tensors with quadrupole coupling constants of 181·9 ± 0·2, 179·9 ± 0·2, 168·1 ± 0·2 and 165·0 ± 2·0 kHz. The corresponding values for the asymmetry factors were 0·103 ± 0·002, 0·125 ± 0·002, 0·038 ± 0·002 and 0·01 ± 0·03. The angles between the directions of the maximum principal components of the first two tensors and hydrogen bond directions predicted from the reported structure are less than 4°. In addition, the directions of the components of intermediate magnitude of the same tensors are within 10° of the perpendiculars to the planes formed from the carboxyl planes and the hydrogen bonds. Thus, an application of Chiba's rules permits a reasonable assignment of the first two tensors. The angle between the maximum principal components of the remaining two tensors, and the angles that these components form with the carbon-carbon single bonds are all close to the tetrahedral angle. It therefore seems plausible to assign the second two tensors to the CH sites. Deuteration of these sites has been confirmed by high resolution N.M.R. of the solution, and by the N.M.R. of the residual protons in the crystal. The latter analysis produced Pake type curves from which a CH bond length of 1·07 ± 0·04 Å was determined.