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1 Dec 1939

Volume 7, Issue 12, pp. 1069-1115


The Lengths of the Links of Unsaturated Hydrocarbon Molecules

C. A. Coulson

J. Chem. Phys. 7, 1069 (1939); http://dx.doi.org/10.1063/1.1750373 (3 pages) | Cited 7 times

Online Publication Date: 22 December 2004

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The lengths of the links in conjugated chain molecules C2nH2n+2 and in condensed aromatic hydrocarbons such as benzene, naphthalene and diphenyl are calculated on the assumption that there is a simple interaction energy between all contiguous carbon‐carbon bonds. The lengths thus deduced are in excellent agreement with those determined by the use of quantum‐mechanical ideas of resonance.

Remarks on the Calculation of Bond Strengths

Milton Burton

J. Chem. Phys. 7, 1072 (1939); http://dx.doi.org/10.1063/1.1750374 (4 pages) | Cited 7 times

Online Publication Date: 22 December 2004

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The hypothesis that predissociation as evidenced by sudden broadening of the rotation lines in an absorption spectrum may be used to establish the strength of the bond involved in the associated photochemical act is re‐examined. It is shown to lead to incorrect conclusions in the few cases where its use seemed applicable. New values are derived for the C☒C and C☒H bond strengths in various compounds. The values are consistent among themselves and with observations in reaction kinetics but show a small spread due to secondary effects of adjacent double bonds. In free acetyl and formyl radicals the bonds are much weaker than in the stable compounds.

The Potential Energy Relationships in Normal and Excited Acetaldehyde

Thomas W. Davis and Milton Burton

J. Chem. Phys. 7, 1075 (1939); http://dx.doi.org/10.1063/1.1750375 (6 pages) | Cited 4 times

Online Publication Date: 22 December 2004

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By a simple modification and extension of the system of potential energy hypersurfaces used to correlate the observations in the thermal and the photochemical decomposition of acetaldehyde it is shown that the following effects are explained: (1) the dependence on temperature and wave‐length of relative probabilities of free‐radical and ultimate molecule production in the primary photochemical act; (2) the disappearance of fluorescence at shorter wave‐lengths or at higher temperatures; (3) the separate maxima for band and continuous absorption; (4) the high quantum yield reported at 3340A.

Chain Length and Chain‐Ending Processes in Acetaldehyde Decomposition

Milton Burton, H. Austin Taylor, and Thomas W. Davis

J. Chem. Phys. 7, 1080 (1939); http://dx.doi.org/10.1063/1.1750376 (6 pages) | Cited 4 times

Online Publication Date: 22 December 2004

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See Also: Erratum

Show Abstract
The C☒C bond strength in acetaldehyde is probably less than a previously postulated value of 93 kcal. and may be as low as the 75 kcal. value calculated by Grahame. The chain‐ending processes in the pyrolysis, in the azomethane‐induced decomposition, and in the photolysis of acetaldehyde are all bimolecular but it is clear that the processes in the second and the third decompositions cannot be identical. The uncertainty of the process in the pyrolysis introduces an uncertainty into Grahame's calculation. In any event, the process is not the combination of methyl radicals in the gas phase to yield ethane. In the photolysis (and perhaps in the pyrolysis) HCO seems to be involved in the chain‐ending reaction. In the induced decomposition CH3CO seems to be concerned. The recombination of methyl radicals as a wall reaction may occur in packed vessels. Activation energies of the various reactions are discussed.

Internal Rotation and Dipole Moment in Succinonitrile

George L. Lewis and Charles P. Smyth

J. Chem. Phys. 7, 1085 (1939); http://dx.doi.org/10.1063/1.1750377 (9 pages) | Cited 12 times

Online Publication Date: 22 December 2004

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A new heterodyne‐beat apparatus has been employed to determine the dipole moment of acetonitrile from —60° to +60° and that of succinonitrile from —90° to +90° in solution. By assuming each half of the succinonitrile molecule to have the same moment as the acetonitrile molecule, the observed moments have been used to calculate the height of the potential barrier which restricts rotation around the carbon‐carbon single bond in succinonitrile and thereby causes the moment of the molecule to increase with rising temperature. The value 1.2±0.5 kcal. thus obtained is in better agreement with the value 1.5 obtained from the calculation of the sum of the various potential energies existing between the two halves of the molecule than is warranted by the necessarily approximate nature of the calculation.

The Intermolecular Potential of Mercury

J. H. Hildebrand, H. R. R. Wakeham, and R. N. Boyd

J. Chem. Phys. 7, 1094 (1939); http://dx.doi.org/10.1063/1.1750378 (3 pages) | Cited 16 times

Online Publication Date: 22 December 2004

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The distribution function for liquid mercury from the melting point up to 250° recently published by the junior authors, has been used to calculate the intermolecular potential by aid of the equation derived by Hildebrand and Wood, E=(2πN2/V)∫ϵWr2dr. This potential is accurately reproduced by the equation, ϵ=j/rn—k/r6, with j=5.49×10‐9 and k=3.52×10‐10, for ϵ in dynes and r in angstroms. The attractive constant, k, checks exceedingly well with the value 3.35×10‐10 calculated by the aid of the London formula for dispersion potential. Several other independent checks agree with the above potential function within the apparent limits of error of each.

Inversion of the Partition Function to Determine the Density of Energy States

S. H. Bauer

J. Chem. Phys. 7, 1097 (1939); http://dx.doi.org/10.1063/1.1750379 (6 pages) | Cited 14 times

Online Publication Date: 22 December 2004

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The density of energy states for a complex system may be deduced from thermodynamic functions when their dependence on temperature is specified. The method is general and depends for its accuracy on the closeness of approximation of the experimentally determined partition function by an appropriate equation. Accurate specific heat data are therefore essential. The degeneracy function is obtained by inverting the Laplace integral defining the sum‐over‐states; as illustrations, the energy states for an Einstein crystal, and for a modified Debye crystal without and with a transition are discussed. The author was not successful in finding a mathematical expression which fitted the last case sufficiently well to differentiate between transitions of first and higher order.
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Kinetics of Phase Change. I General Theory

Melvin Avrami

J. Chem. Phys. 7, 1103 (1939); http://dx.doi.org/10.1063/1.1750380 (10 pages) | Cited 3355 times

Online Publication Date: 22 December 2004

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The theory of the kinetics of phase change is developed with the experimentally supported assumptions that the new phase is nucleated by germ nuclei which already exist in the old phase, and whose number can be altered by previous treatment. The density of germ nuclei diminishes through activation of some of them to become growth nuclei for grains of the new phase, and ingestion of others by these growing grains. The quantitative relations between the density of germ nuclei, growth nuclei, and transformed volume are derived and expressed in terms of a characteristic time scale for any given substance and process. The geometry and kinetics of a crystal aggregate are studied from this point of view, and it is shown that there is strong evidence of the existence, for any given substance, of an isokinetic range of temperatures and concentrations in which the characteristic kinetics of phase change remains the same. The determination of phase reaction kinetics is shown to depend upon the solution of a functional equation of a certain type. Some of the general properties of temperature‐time and transformation‐time curves, respectively, are described and explained.
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Inertial Effects in the Skeletal Vibrations of Tetramethylmethane and Tetramethylsilicon

Samuel Silver

J. Chem. Phys. 7, 1113 (1939); http://dx.doi.org/10.1063/1.1750381 (1 page) | Cited 5 times

Online Publication Date: 22 December 2004

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Abstract Unavailable
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Erratum: Changes of Phase and Transformations of Higher Order in Monolayers

D. G. Dervichian

J. Chem. Phys. 7, 1113 (1939); http://dx.doi.org/10.1063/1.1750382 (1 page)

Online Publication Date: 22 December 2004

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Abstract Unavailable

On The Nature of The Liquid State

William Band

J. Chem. Phys. 7, 1114 (1939); http://dx.doi.org/10.1063/1.1750383 (1 page) | Cited 1 time

Online Publication Date: 22 December 2004

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Abstract Unavailable

The Heat Capacity of Cyanogen Gas

E. J. Burcik and Don M. Yost

J. Chem. Phys. 7, 1114 (1939); http://dx.doi.org/10.1063/1.1750384 (2 pages) | Cited 1 time

Online Publication Date: 22 December 2004

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Abstract Unavailable

The Heat Capacity of Cyanogen Gas

Fred Stitt

J. Chem. Phys. 7, 1115 (1939); http://dx.doi.org/10.1063/1.1750385 (1 page) | Cited 2 times

Online Publication Date: 22 December 2004

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Abstract Unavailable
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