Abstract
The rate of isomerization of
cyclo
propane to propylene is calculated on a theory of unimolecular reactions, which treats a molecule as a classical vibrating system. Isomerization is assumed to occur when the vibrations carry any hydrogen too near to a carbon of another methylene group. The frequency factor found for the high-pressure rate is 4 x 10
14
s
-1
, which is comparable with the experimental value 15 x 10
14
. The decline of the rate
K
from
K
∞
with pressure shows a curve of log
10
(
K
/
K
∞
) against log
10
p
of the correct shape, down to the lowest pressures (under 0.1 mm) of Pritchard, Sowden & Trotman-Dickenson’s recent experiments; but the absolute values of the theoretical pressure for given
K
/
K
∞
are 3½ times those observed. As an alternative model, isomerization is assumed to follow the over-stretching of a carbon-carbon bond; here the high-pressure frequency factor found is only 6 x 10
13
, and this limit is estimated to be approached only at excessively high pressures. In the course of the vibrational analysis, which is based on Saksena’s calculation of the force constants, the detailed classical behaviour of the molecule is found in each of the twenty-one modes of vibration.
Reference11 articles.
1. Chambers T. S. & Kistiakowsky G. B. 1934
2. Glasstone S. Laidler K. J. & Eyring H. 1941 The theory of rate processes chapter in . New York: McGraw-Hill Book Co.
3. Trans;Hamann S. D.;Faraday Soc.,1952
4. Herzberg G. 1945 Infra-red and Raman spectra of polyatomic molecules p. 351. New York: D. Van Nostrand Co.
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