2058
CHAS.E. ~VARINGAND ROBERTL. CUSTER [CONTRIBUTION FROM THE
DEPARTMENT O F CHEMISTRY,
Vol. 76
UNIVERSITY O F C O N K E C T I C U T ]
The Faraday Effect of Some Molecules Chelated or Associated by Hydrogen Bonding BY CHAS.E. WARINGAND ROBERTL. CUSTER’ RECEIVED DECEMBER 8, 1953 It is the purpose of this paper to present absolute Verdet constants of beuzene solutions of 0- and p-nitrophenol and of oand p-nitrochlorobenzene in a n effort t o detect differences in their solute molecular interactions. Apparent molecular Verdet constants, temperature coeficients of molecular Verdet constants and magnetic rotatory dispersions are calculated from the data. Three magneto-optic methods provide additional magtietochemical evidence that the hydrogen bond occurs as ordinary ekctrostatic attraction.
Introduction Recent work on the application of the Faraday effect to problems of chemical structure2has shown that where certain solute molecular interactions occurred, these would be indicated by definite discontinuities in the plot of molecular Verdet constant for the system against the mole fraction of solute. I n extending this work, Waring and co-workers have studied the system acetone-chloroform. The results of this research indicated the necessity for systematic studies of other systems of molecules whose structural characteristics were well known in order to test more fully the ability of the Faraday effect to detect changes in structure. The results obtained in a study of the Faraday effect of water4 indicated that the temperature dependence of the Faraday effect might be an additional means of detecting modifications in electronic structure. Thus, in a system where solute molecular interactions were sufficient to modify the electronic configuration of the molecule to the point where the Faraday effect was able to detect it, a difference in the aspect of the temperature dependence for the system might be expected. Conditioned by an investigation by Rumpf and Seguin5 of the magnetic susceptibility of similar molecules, the ortho and fiara isomers of nitrophenol and of nitrochlorobenzene were selected for a study of the Faraday effect of their solutions in an inert solvent in the concentration range where solute molecular interactions would be expected to become important. It is the purpose, therefore, of this paper to present absolute Verdet constants for benzene solutions of 0- and p-nitrophenol and of 0- and fi-nitrochlorobenzeiie in an effort to detect differences ill their solute molecular interactions.
benzene were Matheson grades No. 5278 and No. 2796, respectively, which were employed without further purification. A comparison between the melting points of these four compounds with those given in the literature is: Xl.p., o c .
o-Nitrophenol p-Nitrop henol o-Nitrochlorobenzene p-Xitrochlorobenzene
Exptl.
Lit.
44.3 112.1 32.7 82.0
456 1146 32.5’ 83. 57
The benzene used to prepare the solutions was reagent grade, thiophene-free and dried over PzOS. This was distilled in a 30-plate Oldershaw column and only those fractions having a refractive index greater than 1.4974,s were collected and stored in glass-stoppered Pyrex bottles until used. The solutions were prepared by weight using ground-glass stoppered Pyrex bottles and a Christian Becker large capacity balance. Corrections for buoyancy and for differences in vapor density in the tare and in the gas space above the material in the solution bottle were made t o all weights. The solute rnolc fractions of the solutions so prepared9 had values of 1, 2, 4, 8 and 16 X 10-3 for the four compounds which were calculated with uncertainties of f0 .05yo. Magnetic rotation constants, k , were measured in the manner previously described3,*over temperature ranges from 10” to 50” for each of the wave lengths 589, 578 and 546 mg. The experimental rotation constants for the solutions were plotted against temperature on large laboratory graphs. From these curves, smoothed data a t arbitrary temperatures were obtained. These data, together with experimental densities for the solutionsg and the experimentally determined magnetic field strength of the solenoid employed,g were used t o calculate specific Verdet constants for the solutions. Molecular Verdet constants were next calculated on the bases of molecular weights for the solutions which were computed from the data on weighings.
Results Apparent inolecular Verdet constants for the solute compounds, V 2 ,were calculated from the relation
Experimental The samples of o-nitrophenol and p-nitrophenol used in making up the solutions were EK P-191 and EK 192, respectively. The former was purified by recrystallizing twice from benzene and then twice from a water-methanol mixture, after which the crystals were dried in a vacuum desiccator. The p-nitrophenol was recrystallized once from a water-methanol solution and dricd in a vacuum desiccator over L-aOH. The o-nitrochlorobenzene and p-nitrochloro(1) T h e d a t a presented were submitted in partial fulfillment of t h e requirements of the l’h.D. degree a t the University of Connecticut. ( 2 ) Chas. E. Waring, et al , THISJ O U R N A L , 62, 2028 (1940); 63,1985 (1941); 65, 1066 (1913): 66, 1068 (1943:. (3) Chas. E . Ix-aring, el a ! . , Rea. S L ~ I . ~ i s t ~ z ~ i n e21, n f ~109 , (1930); S . Steingiser. P h . U . Thesis, University of Connecticut, 1943 ( I ) Chas. 13. \%-=ring and I
