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Spin-lattice relaxation times, second moments and linewidths have been measured in 2,4-dimethylpentane, 2,2,4- and 2,3,4-trimethylpentane from 10 °K to their melting points. Comparison of experimental results with theoretical second-moment values indicates the presence of some reorientation of methyl groups even at the lowest temperatures. At low temperatures the spin-lattice relaxation times are much longer than is usual in the presence of molecular motion. The 2,3,4-isomer can exist in two forms below 130 °K. one form has glass-like properties and also shows a time dependence of T1 at 20 °K.