Marcus E. Hobbs

Electric Polarization of Carboxylic Acids in Dilute Solutions of Nonpolar Solvents I. The Relation of Electric Polarization to the Association of Carboxylic Acids in Hydrocarbon Solvents

The association and polar character of various carboxylic acids have been studied in the solvents benzene and heptane by means of measurements of the electric polarization in very dilute solutions. The data have been analyzed by assuming an equilibrium between dimers and monomers of the acid molecules. A rather large anomalous contribution to the polarization of the dimer has been found. Possible origins of this polarization have been briefly considered.

An Alternating‐Current Apparatus for Measuring Dielectric Constants

A heterodyne beat apparatus operating on alternating current is described. The essential features are: (1) a crystal controlled oscillator, (2) a variable capacitance oscillator, and (3) the power supply. By properly choosing plate potentials and by using a line voltage stabilizer the effects of normal voltage variations have been essentially eliminated. The frequency stability is found to be quite good, and the time of warm‐up rather short. Especial care was given to rigidity of mountings, and to thermostating of both oscillators. Circuit details are shown in figures.

Electric Polarization of Carboxylic Acids II. Polarization of Heavy Acetic Acid and of the Three Fluorobenzoic Acids in Benzene and the Anomalous Polarization of the Dimer

The electric polarizations of acetic acid‐d and o‐ m‐ and p‐fluorobenzoic acids have been determined in benzene solution at concentrations ranging from approximately 10—5 to 10—2 mole fraction of solute. On the assumption of a monomer‐dimer equilibrium, the polarization of the monomer and of the dimer molecules and the equilibrium constant have been calculated. The unexpectedly high polarization of the dimer is best interpreted on the basis of the assumption of an atomic polarization of about 20 cc.

POLARIZATION MEASUREMENTS ON CARBOXYLIC ACIDS IN DILUTE SOLUTION IN NON‐POLAR SOLVENTS

The effective use of dielectric polarization measurements in investigating the association of polar molecules in non-polar solvents has been largely confined to a study of the association of alcohols. These show significant changes in their state of aggregation in a range of concentrations sufEiciently high so that the equipment and methods hitherto available for dielectric constant measurements in solutions can be successfully applied to the investigation of their extent of association. The case of the carboxylic acids in non-polar solvents is quite different. Freezing point determinations show that extremely low concentrations must be attained before significant changes in the state of aggregation occur. This range of concentrations in the case of many of the acids lies below 2 X mole fraction. As a consequence it has been difficult to make sufficiently accurate measurements by most of the methods for molecular weight determination in solution to yield quantitative information about the molecular state of these acids in dilute solution in non-polar solvents. While it has been possible to use the freezing point method, this is applicable only a t a single temperature and so gives information about temperature coefficients and energies of association only through the use of estimates made at other temperatures by other methods. In this paper a description will be given of some of the improvements which were made in apparatus and methods in order to carry out dielectric polarization measurements in very low concentrations in non-polar solvents under anhydrous conditions. In view of the low concentrations involved it is necessary to include a comprehensive statement of the errors of the method. A detailed discussion of the methods employed for interpreting and analyzing the results from the standpoint of the association of the solutes is aIso incIuded.

The Solid State of H2, HD and D2

By using the van der Waals field as calculated for H2 from the second virial coefficient by Lennard‐Jones, and the kinetic zero point energy expression given by London in the theory of liquid He, the lattice energies of solid H2, HD and D2 have been calculated. The values calculated for the energy at 0°K are for H2 —180.4 and for D2 —280.6 calories per mole. These are in good agreement with the experimental values of —183.4 and —274.0 cal./mole, respectively. The corresponding theoretical values of the volume are 23.24 cc (22.65 obs.) for H2, and 19.78 cc (19.56 obs.) for D2. The values of HD have been predicted.