J. G. Aston

Thermodynamic Properties of Gaseous 1,3‐Butadiene and the Normal Butenes above 25°C Equilibria in the System 1,3‐Butadiene, n‐Butenes, and n‐Butane

Tables of the thermodynamic functions Cp0, H0, S0, and F0 are given for 1,3‐butadiene and the normal butenes for temperatures from 298.16°K to 1500°K for the substances in the ideal gas states at one atmosphere pressure. These have been prepared using reliable spectroscopic and molecular data, together with calorimetric entropies, gaseous specific heats, and heats of formation. Equilibrium constants are given for reactions in the system 1,3‐butadiene, n‐butenes, and n‐butane. Available experimental data are compared with the calculations. The calorimetric data for 1,3‐butadiene furnish strong evidence for the existence of two geometric (cis‐trans) isomeric forms of 1,3‐butadiene in appreciable concentrations at room temperatures. The two forms differ in energy by 2.3 kcal. mole−1, and are separated by a C–C rotational barrier 2.6 kcal. mole−1 above the lowest energy level of the cis, or higher, energy form.

An Empirical Correlation and Method of Calculation of Barriers Hindering Internal Rotation

The barriers hindering internal rotation of methyl groups can be calculated by assuming that they are solely due to repulsion between hydrogen atoms according to the law Vij=4.99 ×105/rij5. For dimethyl ether, dimethyl sulfide, and propylene the empirically calculated values are low. This discrepancy is discussed. This treatment is applied to ethyl and isopropyl alcohol and several normal paraffins. The resulting entropies, heat capacities, and equilibrium constants are compared with the available experimental data.

Proton Relaxation in Hexamethylbenzene

Proton T1 and T1ρ of solid hexamethylbenzene have been measured at 30 MHz from 4.2°K to above the melting point. The T1 results are in satisfactory agreement with similar measurements of Allen and Cowking, and of Anderson and Slichter. The T1ρ results confirm their conclusions concerning molecular motion over most of the solid‐phase temperature range, but reveal a previously undetected motion just below the melting point. Mention is made of a method for measuring long T1s in solids.

Interaction of Helium, Neon, Argon, and Krypton with a Clean Platinum Surface

The heats of adsorption of helium, neon, argon, and krypton have been studied on a clean platinum black of high area, prepared using the technique of a thermally indicated titration.These measured heats are compared with the theoretically calculated attractive part of interaction energy between a nonpolar gas and a metal surface.The Margenau and Pollard formulas best represents the measured values. Considering the uncertainty involved due to lateral interaction and the neglected repulsive part of the potential function it is reasonable to say that all of the theories are inagreement with the measured values to the degree of their approximation.

The Entropy of Ethyl Alcohol from Molecular Data and the Equilibrium in the Hydration of Ethylene

The entropy and free energy of ethyl alcohol gas have been calculated from the molecular data at several temperatures on the basis of (a) free internal rotation, (b) restricted rotation (with potentials; about C–C bond=3000, C–O bond=10,000 calories). The latter values are in perfect agreement with those from the third law and from the equilibrium data on the hydration of ethylene.

The vapor pressure of hexamethylbenzene the standard entropy of hexamethylbenzene vapor and the barrier to internal rotation

Abstract The vapor pressure of solid hexamethylbenzene has been measured from 314 to 363 K using the transpiration method. The results are combined with heat capacity measurements to yield revised values of the standard entropies of this substance. A comparison of the experimental entropies with statistical calculations yields revised values of the barrier to internal rotation amounting to 2402 cal mol−1 if one assumes D6h symmetry for the ring carbons, and 3473 cal mol−1 if one assumes S6. It is concluded that the hexamethylbenzene molecule is probably non-planar with S6 ring symmetry.

Thermal Properties of Cyclopentane and Its Use as a Standard Substance in Low Temperature Thermal Measurements

The thermal properties of cyclopentane were redetermined in the Penn State isothermal calorimeter and adiabatic calorimeter B′ and the results compared with other investigations. It is concluded that the heat capacity results of Penn State adiabatic calorimeter B′, those of the National Bureau of Standards, and those of the Bureau of Mines Laboratory at Bartlesville, Oklahoma, are in satisfactory agreement, under normal operating conditions, above 30°K.

The Entropy of Acetone and Isopropyl Alcohol from Molecular Data. The Equilibrium in the Dehydrogenation of Isopropyl Alcohol

The entropy and free energy of acetone and isopropyl alcohol gases have been calculated from the molecular data at several temperatures on the basis of (a) free internal rotation (b) restricted rotation (with the potentials: Acetone, about C–C bond=1000 cal.; isopropyl alcohol, about C–C bond=3400 cal. about C–O=5000 cal.). The values based on restricted internal rotation were made to be consistent with the third law values. They are in better agreement with the ΔS values from the equilibrium data than those assuming free rotation.

Adsorption of Helium on Titanium Dioxide

The absorption characteristics of helium adsorbed on TiO2 (anatase) have been studied in the temperature range 2°—20°K. Isotherms are reported at 2.60°, 4.17°, 13.96°, and 20.28°K. Isosteric heats of adsorption at low coverage have been measured at 17.1°K. The data are interpreted in terms of a previously discussed model.

Molecular Rotation and Translation in Crystals. Nuclear Magnetic Resonance Absorption, Heat Capacity, and Entropy of Crystalline Solid Solutions of 2,2‐Dimethylbutane in 2,3‐Dimethylbutane from 10°K to 273°K

The nuclear magnetic resonance absorption of solid solutions of 2,2‐dimethylbutane (A) and 2,3‐dimethylbutane (B) has been studied as a function of composition. The melting range is clearly marked, but the rotational transition is absent. There is a maximum in the melting point diagram at the composition B2 A3. Thermal data have been determined on this complex from 10°K to 265°K from which the zero‐point entropy has been deduced. The heat capacity curve and zero‐point entropy of the crystals are those of a glass which indicates translational freedom in the rotating crystals.