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1 Dec 1944

Volume 12, Issue 12, pp. 469-522


Bromination of Hydrocarbons. I. Photochemical and Thermal Bromination of Methane and Methyl Bromine. Carbon‐Hydrogen Bond Strength in Methane

G. B. Kistiakowsky and E. R. Van Artsdalen

J. Chem. Phys. 12, 469 (1944); http://dx.doi.org/10.1063/1.1723896 (10 pages) | Cited 49 times

Online Publication Date: 22 December 2004

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The photochemical bromination of methane was studied in the temperature range 423–503°K and found to proceed through the following chain mechanism:
math
Bromination of methyl bromide is analogous and from 7.5 to 10 times more rapid in this temperature range. Hydrogen bromide inhibits bromination of methane but not of methyl bromide. Thermal bromination was studied at 570°K and found to follow the same mechanism as photochemical reaction, except that bromine atoms are produced thermally. The activation energy of photochemical bromination of methane is 17.8 kcal./mole and that of methyl bromide is 15.6 kcal./mole. Varying efficiencies of different molecules as third bodies in the homogeneous recombination of bromine atoms are discussed. Configurations of activated complexes have been assigned and by statistical mechanical calculations shown to be reasonable. Activation energies and other data have been combined to arrive at a value for the C☒H bond strength in methane of 102 kcal./mole at room temperature.

Bromination of Hydrocarbons. II. Photochemical Bromination of Ethane and Ethyl Bromide. Carbon‐Hydrogen Bond Strength in Ethane

Holger C. Andersen and E. R. Van Artsdalen

J. Chem. Phys. 12, 479 (1944); http://dx.doi.org/10.1063/1.1723897 (5 pages) | Cited 16 times

Online Publication Date: 22 December 2004

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The kinetics of the photochemical bromination of ethane was determined. The mechanism is very similar to the analogous brominations of hydrogen and methane:
math
Rate constants computed by assuming various efficiencies for ethane as the third body in step (5) are presented, as well as those calculated by considering heterogeneous recombination of bromine atoms. The rate of bromination of ethyl bromide is about the same as that for ethane, but its exact determination was precluded by the presence of rapidly brominated impurities. The experimental activation energy, 13.6±0.5 kcal., is quite insensitive to the several variations in mechanism discussed, and indicates a value of 98±2 kcal. for the upper limit of the strength of the C2H5☒H bond. This figure is in good agreement with absolute values reported by other workers.

The Mercury Photosensitized Polymerization and Hydrogenation of Butadiene

H. E. Gunning and E. W. R. Steacie

J. Chem. Phys. 12, 484 (1944); http://dx.doi.org/10.1063/1.1723898 (10 pages) | Cited 13 times

Online Publication Date: 22 December 2004

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An investigation has been made of the mercury (3P1) photosensitized polymerization and hydrogenation of butadiene. The main products of the reaction of butadiene with mercury (3P1) atoms are hydrogen, an acetylenic compound in the C4 fraction, dimer, and polymer. In the presence of excess hydrogen, the products are mainly butane, butene, and octanes. The variation of the rate of the polymerization reaction with time, and with the pressure of butadiene, suggests the following mechanism: C4H6+Hg(3P1)→C4H6*+Hg(1S0), followed by C4H6*+C4H6→2C4H6, or C4H6*+C4H6→(C4H6)2 or C4H6*→C4H4+H2. Polymerization arises largely by a free radical mechanism H2+Hg(3P1)→2H+Hg(1S0),H+C4H6→C4H7,C4H7+C4H6→C8H13, etc. The mechanism is shown to be consistent with the value found for the quantum yield.

The Tetrahedral X2YZ2 Molecular Model Part I. Classical Vibration Problem

W. H. Shaffer and R. C. Herman

J. Chem. Phys. 12, 494 (1944); http://dx.doi.org/10.1063/1.1723899 (10 pages) | Cited 10 times

Online Publication Date: 22 December 2004

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Appropriate coordinates are set up from the standpoint of group theory for describing the normal modes of oscillation in such a manner that maximum factorization of the secular determinant is accomplished. The cubic and quartic portions of the anharmonic potential function are derived. The components of vibrational angular momentum are set down. The complete valence‐type potential function is discussed; explicit relations are derived between the generalized force constants occurring in the secular determinant and the valence force constants for CH2D2.

The Infra‐Red Spectra of Bent XYZ Molecules Part I. Vibration‐Rotation Energies

W. H. Shaffer and R. P. Schuman

J. Chem. Phys. 12, 504 (1944); http://dx.doi.org/10.1063/1.1723900 (10 pages) | Cited 19 times

Online Publication Date: 22 December 2004

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See Also: Erratum

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The rotation‐vibration Hamiltonian, complete to second order of approximation, is set up for the bent XYZ molecular model. The allowed energies are calculated and expressed in term‐value form, E=hc(G+F); the vibrational term G is given explicitly and the elements of the secular determinant are given for evaluation of the rotational term F. The valence‐force form of harmonic potential function is discussed for the bent XYY′ model and normal frequencies of HDO are calculated.

Electrical Anisotropy of Xerogels of Hydrophile Colloids. Part II

S. E. Sheppard and P. T. Newsome

J. Chem. Phys. 12, 513 (1944); http://dx.doi.org/10.1063/1.1723901 (7 pages) | Cited 1 time

Online Publication Date: 22 December 2004

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An improved, though still relative, quantitative expression has been derived for the electrical anisotropy E. A. The E. A. is a linear function of the elongation up to a certain limit, as is also the optical birefringence. The relation of electrical to optical anisotropy has been studied in greater detail. A more critical discussion in terms of atomic model structures is given of the hypothesis that E. A. in the compounds studied is due to the formation of continuous parallel chains of hydrogen bridges, having electronically conducting character: The materials studied were: polyvinyl acetate and its hydrolyzed stages down to polyvinyl alcohol, cellulose acetate and its hydrolyzed stages down to (hydrate) cellulose.
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Photography of Crystal Structures

Maurice L. Huggins

J. Chem. Phys. 12, 520 (1944); http://dx.doi.org/10.1063/1.1723902 (1 page) | Cited 8 times

Online Publication Date: 22 December 2004

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Errata : On the Statistical Mechanics of Liquids, and the Gas of Hard Elastic Spheres

O. K. Rice

J. Chem. Phys. 12, 521 (1944); http://dx.doi.org/10.1063/1.1723903 (1 page) | Cited 1 time

Online Publication Date: 22 December 2004

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Erratum: The Chain Photolysis of Acetaldehyde in Intermittent Light

W. L. Haden and O. K. Rice

J. Chem. Phys. 12, 521 (1944); http://dx.doi.org/10.1063/1.1723904 (1 page)

Online Publication Date: 22 December 2004

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Abstract Unavailable

Bond Moments of Higher Valence States

R. Samuel

J. Chem. Phys. 12, 521 (1944); http://dx.doi.org/10.1063/1.1723905 (2 pages)

Online Publication Date: 22 December 2004

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