Abstract
The thermal unimolecular isomerization of hexa-1,
trans
-3, 5-triene to the
cis
-compound is shown to obey the rate expression
k
1
= (4.5 ± 1.5) x 10
12
exp( — 181.3 + 2.0 kJ mol
-1
/
RT
) s
-1
. At low pressures of cyclohexa-1, 3-diene, it undergoes a thermal unimolecular conversion to benzene and hydrogen via cyclohexa-1, 4-diene; the Arrhenius parameters found for this process are
k
2
= (4.7 ± 2.2) x 10
13
exp (— 258 ± 4 kJ mol
-1
/
RT
) s
-1
. From these, other kinetic and thermodynamic data, the theory of unimolecular reactions was used to calculate the quantum yields of the main products in the gas phase photolyses of
cis
- and
trans
- hexa-1, 3, 5-triene and cyclohexa-1, 3-diene as a function of pressure. Good agreement with experiment was obtained assuming that all the observed photochemical reactions involved vibrationally exoited molecules formed by internal conversion of the initially populated excited electronic state. A limited amount of
cis-trans
isomerization may occur in the excited electronic states of the hexatrienes. A step-ladder deactivation model with ∆
E
= 25 kJ mol
-1
for the parent molecule gave good agreement with the experiments, in which there is clear evidence of multi-step quenching. It is deduced from their photochemistry that the
trans
and
cis
hexa-1, 3, 5 trienes differ in enthalpy by 11 kJ mol
-1
.
Reference15 articles.
1. Proc. E;Soc. Lond. A,1970
2. B ack M. H . 1970 In t. J . chem. K inetics 2 409.
3. chem;Staples C. E .;Soc.,1963
4. Benson S. W . 1968 Thermochemical kinetics. New Y o rk : W iley.
5. J . A m . chem;Benson S. W .;Soc.,1967
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