A Nuclear Magnetic Resonance and Relaxation Study of Dimethoxyborane.

Abstract

Proton and boron-11 c.w. nuclear magnetic resonances have been studied in solid H11B(OCD3)2 and H10B(OCD3)2. For 11B, only the transition, broadened by second order quadrupolar effects and by proton dipolar interaction can be seen; from the spectrum at several rf frequencies, the quadrupolar coupling constant |e 2 qQ/h| was found to be 3.0 ± 0.2 MHz (± always refers to rms errors). In H10B(OCD3)2, the proton line shapes at 53 and 10 MHz are considerably different; this may be interpreted as due to changes in the directions of 10B nuclear quantization. Nuclear magnetic relaxation studies have been made in the liquid phase. From the 10B and 11B relaxation times, the activation energy for molecular reorientation was found to be 8.7 ± 0.4 kJ/mol (2.1 ± 0.1 kcal/mol). Consistent values for |e 2 qQ/h| were obtained from relaxation measurements in liquid phase and from c.w. spectra in solid phase. The temperature dependence of proton relaxation times deviates significantly from the activation energy model at higher temperatures, where spin-rotation interactions may be important. Proton transverse relaxation times (T 2) have also been measured and are consistent with the Allerhand-Thiele theory.