Pressure dependence of proton spin-lattice relaxation in liquid hydrocarbons

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Abstract
The pressure dependence of the proton spin‐lattice relaxation timeT 1 in ten liquid hydrocarbons at room temperature (28°C) is reported. The ten compounds were (a) bicyclohexyl, (b) dicyclohexyl methane, (c) 1,3‐dicyclohexyl propane, (d) 1,4‐dicyclohexyl butane, (e) 1,9‐dicyclohexyl nonane, (f) 1,1‐dicyclohexyl ethane, (g) 1,2‐dicyclohexyl propane, (h) 1,3‐dicyclohexyl butane, (i) 1,3‐dicyclohexyl‐2‐methyl propane, and (j) phenyl cyclohexyl. The maximum pressure attained was 3000 kg cm−2. Three compounds (a), (b), and (d) froze before this limit was reached. Three others (c), (e), and (h) gave evidence of higher order phase transitions. Three of the compounds (f), (g), and (i) showed T 1 minima, all around 0.017 sec. The resonant frequency was 20.00 MHz. The volume of activation Δ V ‡ for the molecular correlation time τ c is estimated for each compound. Δ V ‡ is nearly the same for (b), (c), (d), and (e). It is slightly lower for (a) and (j) and slightly higher for the rest. The significance of this and the value of τ c at one atmosphere is discussed. It is felt that the reorientation of the cyclohexyl rings dominates the relaxation procsss.