A. Greenville Whittaker

Nuclear Magnetic Resonance Studies of Solvent Effects on the Hindered Internal Rotation of N,N‐Disubstituted Amides. I. Dimethylformamide

A number of chemical‐shift measurements were made on dimethylformamide (DMF) as a pure liquid and in the solvents carbon tetrachloride, acetone‐d6, fluorotrichloromethane, and hexamethyldisiloxane. These measurements included (1) the temperature dependence of the methyl‐doublet separation, (2) the effect of solvent and concentration on the methyl‐doublet separation, and (3) the effect of temperature, solvent, and concentration on the chemical shift of the formyl proton resonance and on the center of the methyl doublet. The results show large solvent effects that are interpreted in terms of dipolar association between DMF and solvent. No evidence for hydrogen‐bonded species was found. Activation energies for the barrier to hindered rotation were calculated and were found to depend strongly on the nature of the solvent.

Magnetic Susceptibility, Freezing Point Diagram, Density, and Spectral Absorption of the System Vanadium Tetrachloride-Carbon Tetrachloride

On the basis of results of freezing point lowering experiments, it was reported by Simons and Powell that an equilibrium existed between VCl_4, and V_2Cl_8 in carbon tetrachloride solution. Since vanadium tetrachloride is an odd molecule, it was implied that dimerization could take place, as in nitrogen dioxide, such that the odd electrons become paired. In the present paper are reported the results of a study on the system by means of magnetic susceptibility measurements, freezing point diagram determination, and spectral absorption of the solution, as a function of concentration of vanadium tetrachloride in carbon tetrachloride.

Spectrophotometric Study of the Liquid‐Phase Equilibrium N2O4⇌2NO2 in Pure Nitrogen Tetroxide

The liquid‐phase equilibrium constants for the reaction N2O4⇌2NO2 in pure nitrogen tetroxide were measured over the normal liquid range of the substance. The NO2 concentration in the liquid was determined by comparing its light absorption in the liquid with the absorption of a known concentration in the vapor. The results gave a linear relation between log equilibrium constant, and the reciprocal of the absolute temperature. An average heat of dissociation of N2O4 in the liquid phase of 19.5 kcal/mole was obtained.

Magnetic Susceptibility Study of the Liquid Phase Equilibrium N2O4⇌2NO2 in Pure Nitrogen Tetroxide

The magnetic susceptibility of liquid nitrogen tetroxide was measured by the Gouy method over the temperature range 0°C to 30°C. The liquid was found to be diamagnetic throughout this temperature range although the diamagnetism decreased as the temperature increased. The magnetic measurements were found to be in good agreement with the spectrophotometrically determined equilibrium composition of the liquid as reported by Steese and Whittaker.

Proton Resonance Shifts for the Systems HNO3–H2O and HNO3–KNO3

Proton resonance shifts have been measured for the concentrated region of the nitric acid‐water system and also for the system nitric acid‐KNO3. The nitrate ion is very effective in unshielding the protons of nitric acid and further information is presented on the solvation of this ion in the anhydrous acid. Chemical shifts in nitric acid‐water solutions are interpreted in terms of the associated nature of nitric acid. The effect of the self‐ionization of anhydrous nitric acid on the chemical shift for this liquid is evaluated. Also, it was found that the chemical shift could be used for very accurate analysis of nitric acid‐water mixtures in the concentrated acid region.