Showing papers in "Journal of the American Chemical Society in 1947"

Atomic Radii and Interatomic Distances in Metals

Abstract: The problem of the nature of the interatomic farces in the elementary metals and in intermetallic compounds and other alloys continues to be puzzling, despite the clarification of some questions which has been provided by quantum mechanical considerations. It has been my opinion, contrary to that of other investigator that the metallic bond is very closely related to the covalent (shared-electron-pair) bond, and that each atom in a metal may be considered as forming covalent bonds with neighboring atoms, the covalent bonds resonating among the available interatomic positions. It was shown in the first paper of this series that the number of covalent bonds resonating among the available positions about an atom (the metallic valence of the atom) increases from one to nearly six (5.78) in the sequence K, Ca, Sc, Ti, V, Cr in the first long period of the periodic table, remains nearly constant from Cr to Ni, and begins to decrease with Cu. This concept, which is substantiated by the magnetic properties of the metals and their alloys, provides a qualitative explanation of many properties of the transition metals (including those of the palladium and platinum groups), such as characteristic temperature (heat capacity at low temperatures), hardness, compressibility, coefficient of thermal expansion, and the general trend of interatomic distances. It will be shown in the following pages that it also permits the formulation of a system of atomic radii which can be used for the calculation of interatomic distances in metals and intermetallic compounds and for the interpretation of observed interatomic distances in terms of the electronic structure of the crystals. These atomic radii (which may be called metallic radii) are found, as expected, to show an intimate relation to the covalent radii of the atoms-a relation which, in its general nature, permitted Goldschmidt over twenty years ago to use data taken from both metals and ordinary covalent crystals in formulating a table of atomic radii, and which has been recognized3 as providing very strong support for the concept that metallic bonds are essentially resonating covalent bonds.

Reduction of Organic Compounds by Lithium Aluminum Hydride. I. Aldehydes, Ketones, Esters, Acid Chlorides and Acid Anhydrides

Abstract: weight-average molecular weight of M = 40 X 106 with a probable error of 5%. In this determination of the molecular weights from light scattering no assumptions need be made about the percentage of hydration of the particles. If the length and molecular weight of the particles as determined by the light scattering measurements are used with a value of 0.73 for the partial specific volume of the virus, the diameter of the cylindrically shaped virus particles can be calculated to be 15.2 mp. This value is in agreement with that obtained in X-ray'22 and electron microscope16 studies. Summary Light scattering measurements were made on a freshly prepared sample of purified tobacco mosaic virus. The length of the particles determined from dissymmetry of light scattered by the solutions were found to be 270 mp. Application of the dissymmetry to turbidity measurements gave a weight average molecular weight of 40 millions for the particles. These values are in complete agreement with sizes determined from electron microscope and viscosity studies made on the same sample. This agreement indicates the validity of the light scattering method. For dilute solutions of tobacco mosaic in water the dissymmetry decreases with increasing virus concentration thus indicating that strong interaction with a consequent increase in order of the scattering particles is occurring. However, the dissymmetry is independent of concentration for dilute solutions of the virus in 0.1 M sodium phosphate buffer a t pH 7.

The thermodynamic properties and molecular structure of cyclohexane, methylcyclohexane, ethylcyclonexane and the seven dimethylcyclohexanes.

Abstract: This paper is a continuation of studies on the structural and thermodynamic properties of hydrocarbons. As compared to cyclopentane,b in which a large number of configurations with nearly equal stability result from the opposition of torsional forces about single bonds against forces tending to maintain tetrahedral angles, cyclohexane has one predominant stable configuration, the chair form, since it lies at the minimum in potential energy of each type. Other, higher energy tautomers exist in quite small amounts at room temperature. The energies of these, however, are low enough so that they may contribute to thermal properties. We' have recently measured the heat capacity of gaseous cyclohexane and methylcyclohexane and these data are compared with calculated values in the present paper. In the course of our study very interesting effects of geometrical tautomerism in disubstituted cyclohexanes became apparent. These have been mentioned briefly in a communication to the editor,sa but further details are given in this paper. These compounds are important as constituents of petroleum hence their properties should have considerable practical interest. We shall first discuss the work on cyclohexane in some detail and then briefly describe the less detailed calculations on its derivatives.