D. P. Stevenson

The Thermodynamic Properties of Phosphorus, Phosphine, and Some Phosphorus Halides

A critical study of the equilibrium and molecular data for phosphorus and some of its compounds has been made and is described. The data are used to calculate the entropies and free energies of the substances considered.

On the Stable Relative Orientation of Groups Connected by a Carbon‐Carbon Single Bond

Langseth and his co-workers [1] have recently applied the results of essentially incomplete spectroscopic studies of liquid cyclohexane, symmetrical tetrachloroethane, and ethylene deuterobromide to a discussion of the intramolecular forces restricting internal rotation about the C-C bond. We believe that none of their structural conclusions is correct. Their discussion is based on their conclusion that in these molecules the opposed or eclipse configurations are the stable ones. Insofar as liquid cyclohexane and symmetrical tetrachloroethane are concerned this conclusion is most probably incorrect since it directly contradicts the results of a great number of more straightforward studies of these and similar molecules.

The Thermodynamic Functions of Cyanogen and the Cyanogen Halides

The free energy function, heat content and heat capacity of cyanogen and the cyanogen halides, ClCN, BrCN and ICN, have been calculated for a series of temperatures from spectroscopic and electron diffraction data. Since no experimental value for the carbon‐iodine distance has been as yet obtained, an extrapolation is made from the values for the carbon‐chlorine and carbon‐bromine distances in the corresponding cyanogen compounds. 1.96±0.04A is obtained for the I–C distance in cyanogen iodide. The free energies of formation of gaseous (CN)2, ClCN and ICN have been calculated from thermal and equilibrium data. The values of ΔF°298.1 are, 69.1 kcal./mole for (CN)2, 35.5 kcal./mole for ClCN, and 46.75 kcal./mole for ICN. It is estimated that for gaseous BrCN ΔF°298.1=40 kcal./mole.

The Structure of Phosphine and Related Hydrides

It is shown that Badgers rule when applied to the frequencies of some hydrides gives values for the interatomic distances which are in agreement with values deduced from the moments of inertia of the hydrides and with values predicted from the covalent radius suggested for hydrogen, 0.315A. Using the value 1.415A. for the phosphorus‐hydrogen distance in phosphine and a reliable spectroscopic value for one of the moments of inertia of the molecule one finds the bond angle to be 93°. Values are suggested for the bond angles and bond distances in a number of hydrides whose structures have not been experimentally determined.