876. Physical properties and chemical constitution. Part XXXVII. The electric dipole moments of some phenyl-substituted 2-phenylpyridines

Abstract

The electric dipole moments of the three 2-tolylpyridines and of 2-(4-bi-phenyly1)-, 2-+-nitrophenyl-, and 2-p-aminophenyl-pyridine have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene a t 25-00'. Information is obtained about the additivity of the component group moments in these molecules. Internal rotation is restricted, but for 2-0-and 2-m-tolylpyridine the dipole moment value does not suggest preference for a configuration with the methyl group either cis or trans to the nitrogen atom.THE electric dipole moments of phenylpyridines were considered in the preceding paper.1 The phenyl group itself has no primary moment, yet, in the compounds studied, there were substantial apparent phenyl group moments, the largest being that for 2-phenylpyridine (0.66 D). The question arises whether this phenyl group moment should be included in a vector analysis of the dipole moment of a substituted phenylpyridine. Another problem is whether substituents in the phenyl group of the non-planar 2-phenylpyridine molecule prefer a cis-or a frans-configuration with respect to the nitrogen atom. Some 2,Z'-disubstituted biphenyls are known to have a preferred slightly cis-orientation,2 but in 2,2'-bipyridyl and some 3,3'-disubstituted biphenyls the trans-configuration is preferred. The dipole moments of a few substituted 2-phenylpyridines have been measured to provide some data for these problems. EXPERIMENTAL AND RESULTSThe apparatus, experimental techniques, and method of calculation and of presenting the results are as described in previous Parts 495 of this series. The measured properties of the benzene solutions a t 25.00" are presented in Table 1 and the slopes of the linear graphs of dielectric constants (a) and of specific volume (p) against weight fraction, together with the polarisation data and dipole moments, are collected in Table 2.Prefiaration and Purafication of Compounds.-The final purification of each compound was carried out immediately before its dipole moment was measured. The infrared and ultraviolet spectra of the compounds were also determined.4-Biphenylyl-lithium, prepared from lithium and recrystallised 4-bromobiphenyl (m. p. 89') in ether, was treated with a pure pyridine (b. p. 115.3'/762 mm.) in sulphur-free toluene.The fraction of b. p. 180-191"/1 mm. was collected, the base was converted into the picrate, and the latter recrystallised from acetone to constant m. p. (190-191").The regenerated base was recrystallised from alcohol to constant m. p.