A 35C1 nuclear quadrupole resonance study of the trimethylamine -boron trichloride complex has revealed line-width and frequency changes which correlate with transitions observed in the wide-line proton magnetic resonance study.Canadian Journal of Chemistry, 48, 1976 (1970)
IntroductionIn a recent wide-line nuclear magnetic resonance (n.m.r.) study of molecular motions in complexes of trimethylamine with boron trihalides and borane, line-width and secondmoment transitions were observed and attributed to methyl group reorientation in the temperature range below 110 O K , followed by rotation of the trimethylamine group about the B-N axis at higher temperatures (1). For the borane and boron trifluoride complexes it is probable that reorientation of these groups occurred prior to the onset of rotation of the trimethylamine group. It was not possible to determine from these studies whether or not motion of the BCI, or BBr, groups occurred, although the activation energies determined from line-width analyses were about 9 kcal mole-' for trimethylamine rotation compared with about 2 kcal mole-' for the same process in the BF, and BH, complexes. This suggested that the molecule rotates as a whole rather than uncorrelated motion of the two halves.We have examined the frequency and "apparent" line widths of the 35C1 nuclear quadrupole resonance as a fuilction of temperature in the trimethylamine -boron trichloride complex to obtain additional information on the molecular motion in these compounds.The nuclear quadrupole resonance (n.q.r.) frequencies of a series of boron trichloride complexes were first reported by Kaplansky and Whitehead (2). For the trimethylamine complex at 77 OK, two lines were observed, at 21.765 and 21.340 MHz, with an intensity ratio of 2:l.