The electric dipole moments of three phenanthrolines, four bipyridyls, and 2,2'-biquinolyl have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene a t 25.00". They are discussed in terms of the dipole moments expected by the vector addition of the moments of two pyridine molecules and of the interaction between them.
Several methods other than colorimetric, are available for the determination of sterols. These methods may be summarised, in ascending order of sensitivity, as follows: gravimetric, involving the precipitation of 3-P-hydroxy steroids with digitonin (W i n d a u s , 1910; L i n f o r d , 1956; H a u s t et al., 1966; V a h o u n y et al., 1960); flourometric (A1 b e r s and L o w r y , 1955); gas liquid chromatographic for cholesterol (B 1 o o m f i e 1 d , 1962; S c h m i d t and M a t h e r 1964; W i l-Cowley et al., Sterols in Digitalis Bd. 19, Heft 3 Plant Material Seeds of D.prrrpurea were obtained from Verenigde Nederlandse Kruidencooperatie G. A., Elburg, Holland. The leaves were obtained from mature second year plants grown from seed. Chemicals The reference sterols p-sitosterol and ergosterol, were obtained from R. N. Emanuel Ltd., and stigmasterol from Koch Light Ltd. The compounds were purified by thin layer chromatography on 1 mm layers of silica gel G activated a t 120° C for 45 rnin, and developed wth chloroform: methanol (99 : 1). They were recovered by elution with chloroform and recrystallised from acetone. W e are grateful to Dr. B a i s e d for a sample of campesterol. Reagents Solutions of the purified sterols, Tables I-IV, were made up in glacial acetic acid and stored at 25' C for 30 rnin prior to use. The colour reagent, acetic anhydride containing 5% of sulphuric acid, was also kept for 30 rnin a t 2. 5' C before use, and was not used after 40 min, from the time of preparation. The acids and the acetic anhydride were of analytical reagent grade.
The electric dipole moments of three phenylpyridines, six of the phenylquinolines, 2,6-diphenylquinoline, 5-phmylacridine, and 9-phenylphenanthridine have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene at 25.00". The dipole moments of acridine and phenanthridine were also determined. The apparent group moment of the phenyl substituent in these molecules is discussed in terms of conjugation between the phenyl group and heterocyclic ring and of the moments induced in the phenyl group.THE electric dipole moments of the methylpyridines and methylquinolines were measured and discussed in earlier papers of this series. These results are now extended to the corresponding phenyl derivatives. Replacement of a hydrogen atom in a heterocyclic ring by a phenyl group should not introduce a second primary moment into the molecule.? Consequently the difference between the dipole moments of the substituted molecule and the parent compound must arise through electron displacements within the molecule. This will be caused largely by polarisation of the phenyl substituent and by a change in the x-electron distribution. Sobczyk recently discussed the dipole moments of a few of these compounds entirely in terms of the moment induced in the phenyl substituent by the primary moment of the parent heterocyclic molecule, but this factor alone cannot explain all our results. EXPERIMENTAL AND RESULTSThe apparatus, experimental techniques, method of calculation, and presentation of the results are as described in previous Parts.l, * 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 constant (a) and of specific volume (p) against weight fraction, together with the polarisation data and dipole moments (p) are in Table 2.Preparation and Purification of Compounds .-Each compound was purified immediately before its dipole moment was determined. Their infrared and ultraviolet spectra, and their m. p.s and those of their picrates were in good agreement with published data where available.A mixture of the three monophenylpyridines was prepared by the method of Haworth, Heilbron, and Hey4 by the action of benzenediazonium chloride on pyridine. The isomers were separated by fractional recrystallisation of their picrates from alcohol and from acetone. These had m.p.s identical with those of the same compounds obtained by the following unambiguous procedures.2-Phenylfiyridine. Evans and Allen's method was employed in which phenyl-lithium, formed under anhydrous conditions from bromobenzene and lithium in ether, was treated with pyridine in sulphur-free toluene under nitrogen. The mixture was hydrolysed with water and the 2-phenylpyridine isolated from the toluene layer by fractional distillation. Purification was effected by recrystallising its picrate from acetone to a constant m. p. ( 177-5-178-6°) and * Part XXXV, J., 1962, 1188. t The G-H bond moment may vary with the hybrid...
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.
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