The Possibility of Free Rotation in Crystalline Dimethyl Acetylene.
ILLINOIS UNIV URBANA NOYES CHEMICAL LAB
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Crystalline dimethyl acetylene CH3-CC-CH3DMA was investigated by broad line and pulsed proton magnetic resonance in the temperature interval 217-77K. The NMR second moment and line shape at 77K along with the fact that a change was not noticed in the free induction decay following a 90 degree pulse in the experiments, agree with the presence of only methyl group rotation about the C-C axis in the entire temperature region of investigation. From the temperature dependence of the spin-lattice relaxation time T1 it was found that the CH3 group rotation in the low temperature phase is fast and its activation energy is 830 plus or minus 40 Calmole. Also discussed are other possible relaxation mechanisms which could occur in the high temperature phase besides the dipolar one. The phase transition in DMA is discussed in view of available thermodynamic and X-ray as well as our NMR data. Author
- Atomic and Molecular Physics and Spectroscopy