Knowledge Bank

Spin-lattice relaxation $T1$ values have been measured in the temperature range $77\circ K$ to $273\circ K$ for protons in solid methylchlorosilanes by a pulsed nmr spectrometer operating at 28.0 MHz. In addition, line shapes and line widths for the corresponding proton nmr spectra have been recorded at 26.0 MHz by a rapid passage technique employing a Fabritek 1062 signal averager. Barriers to methyl group rotation were found to be 2.34 kcal/mole for $(CH3)3SiCl$ (compared with 3.0 kcal/mole found spectroscopically by Durig, Carter and Li), 1.95 kcal/mole for $(CH3)2SiCl2$ and 1.66 kcal/mole for $CH3SiCl3$ (compared with 1.3 kcal/mole found by McIntyre and Johnson from $T1$ measurements). The barrier for overall rotation of the $(CH3)3Si$ group about the $C3$ axis in trimethylchlorosilane was found to be 7.4 kcal/mole from both $T1$ and linewidth measurements.