14N NMR single-crystal study of hexamethylenetetramine

The 14N NMR spectrum of hexamethylenetetramine (HMT) is dominated by the very large electric quadrupole coupling constant of 4.412 MHz at room temperature. Nonetheless, by carefully accounting for this interaction one can subtract its first- and second-order effects on the spectrum, leaving the much smaller anisotropic chemical shift interaction. The chemical shielding anisotropy of HMT is −8.3±3.2 ppm, small but different from zero, with an isotropic chemical shift in good agreement with the value in aqueous solution. This study illustrates how even very tiny chemical shift tensors can be extracted from the NMR spectra of quadrupolar nuclei using appropriate techniques. Copyright © 1999 John Wiley & Sons, Ltd.