Self-Diffusion Coefficients and Rotational Correlation Times in Polar Liquids. IV. Dichloromethane and Pyridine

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Abstract
Self-diffusion coefficients (D) have been measured in dichloromethane and pyridine from the freezing points to the normal boiling points. The data for CH2Cl2 are represented by D=(2.3± 0.6)10−3exp[−(2.40± 0.15)/RT] cm2sec−1, and the data for C5H5N are given by D=(5.9± 1.5) × 10−3exp[−(3.45± 0.15)/RT] cm2sec−1. Intramolecular proton, deuterium, and chlorine-35 relaxation rates were measured in dichloromethane from 178 to 310°K. The results demonstrate that the rotational correlation time is anisotropic; the proton and chlorine values differ by a factor of 2. The activation energy for relaxation is essentially the same for H, D, and Cl and equal to 1.81± 0.08 kcal mole−1. The present relaxation results and the relaxation data of Kintzinger and Lehn on pyridine are interpreted by means of the quasilattice random flight model generalized to the case of anisotropic rotators. The agreement between the calculated and observed relaxation rates is good for pyridine and fair for CH2Cl2. Calculated pre-exponential factors D0 are 1.8× 10−3 cm2sec−1 for CH2Cl2 and 2.5× 10−3 for C5H5N.