C-13 CP Mas NMR-Study OF A pHENYL Group Rotation int he Solid-State Using T (1-RHO), lineshape and 2D EXSY Measurements

A combination of solid-state C-13 CP/MAS NMR methods was used to study the rates of rotation of the phenyl group in 3,5-dimethyl-1-phenylhex-1-yn-3-ol. The methods used were T1rho measurements, lineshape analysis and 2D exchange spectroscopy over the temperature range 219-284 K. The rates of rotation obtained from the lineshape and 2D EXSY methods give an energy of activation of 58.6 +/- 3.0 kJ mol-1. In good agreement with this, the T1rho measurements give an activation energy for the rotation of 58.7 +/- 3.6 kJ mol-1. The two sets of data are shown to be compatible, within experimental error, with a calculated value for the dipolar carbon-hydrogen interaction (B) from an assumed molecular geometry.