The Journal of Physical Chemistry A
ARTICLE
Table 15. Wiberg Bond Index of Reactant (R), Transition
State (TS), and Products (P) for 2,2-Diethoxypropane Ther-
mal Decomposition from PBEPBE/6-31++G(d,p)
’ ASSOCIATED CONTENT
S
Supporting Information. IRC obtained from gas-phase
b
elimination reaction kinetics of 2,2-diethoxypropane and 1,
1-diethoxy-cyclohexane. This material is available free of charge
C1ꢀC2
C2ꢀO3
O3ꢀH4
H4ꢀC1
Sy
BiR
0.9995
1.2058
1.8099
25.46
0.9338
0.2809
0.0004
69.95
0.0021
0.2010
0.7442
26.80
0.9133
0.6067
0.0001
33.57
0.735
BiTS
BiP
’ AUTHOR INFORMATION
%Ev
Corresponding Author
*E-mail: chuchani@ivic.gob.ve.
Table 16. Wiberg Bond Index of Reactant (R), Transition
State (TS), and Products (P) for 2-Ethoxypropene Thermal
Decomposition from MPW1PW91/6-31G(d,p)
’ REFERENCES
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186–188.
C1ꢀC2 C2ꢀO5 O5ꢀC6 C6ꢀC7 C7ꢀH8 H8ꢀC1
Sy
BiR
1.8306 1.0011 0.8848 1.0337 0.9200 0.0001
0.931
BiTS 1.3870 1.3947 0.3843 1.4203 0.4771 0.3675
BiP
1.0139 1.8169 0.0049 2.0364 0.0000 0.9054
%Ev 54.32 48.25 56.88 38.56 48.14 40.58
(7) Mora, J. R.; Dominguez, R. M.; Herize, A.; Tosta, M.; Chuchani,
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Table 17. Wiberg Bond Index of Reactant (R), Transition
State (TS), and Products (P) for 1,1-Diethoxycyclohexane
Thermal Decomposition from PBEPBE/6-31G(d,p)
C1ꢀC2
C2ꢀO3
O3ꢀH4
H4ꢀC1
Sy
BiR
BiTS
BiP
0.9762
1.1888
1.7433
27.71
0.8958
0.2830
0.0082
69.04
0.0023
0.2037
0.7120
28.38
0.9049
0.5886
0.0203
35.76
0.761
%Ev
Calculated bond orders indicate that the most advanced re-
action coordinate is the breaking of CꢀO bond, being more
important for the 1,2-elimination processes of 2,2-diethoxypro-
pane and 2,2-diethoxycyclohexane, 69ꢀ70%, than the decomposi-
tion of 2-ethoxypropene, 57%. In the 1,2-elimination reaction,
the other reaction coordinates are less advanced as compared to
the CꢀO bond breaking, indicating a nonsynchronous process,
Sy values 0.74ꢀ0.76. Conversely, in the 2-ethoxypropene decom-
position, the progress is intermediate in reaction coordinates
C1ꢀC2, C2ꢀO3, O5ꢀC6, and C7ꢀH8 and somewhat less ad-
vanced for C6ꢀC7 and H8ꢀC1; overall, the process is more
synchronic, Sy = 0.93.
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V. CONCLUSIONS
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The thermal decomposition reactions of 2,2-diethoxypropane
and 1,1-diethoxy-cyclohexane have been studied by experimental
and theoretical methods to propose a reasonable mechanism.
These reactions were demonstrated to be unimolecular, homo-
geneous, and follow first-order kinetics under the experimental
conditions used. These compounds undergo 1,2-elimination
reactions through nonsynchronous four-membered cyclic TS
processes. The 2,2-diethoxypropane gives ethanol and the inter-
mediate compound 2-ethoxypropene, which further decomposes
through a concerted six-membered cyclic TS mechanism to give
acetone and ethylene. The 2-ethoxypropene decomposition is
more synchronic than the 1,2-elimination reactions. The rate-
determining step of these elimination reactions is the polariza-
tion of the CꢀO bond, in the sense of Cδ+
Oδꢀ, in the
3 3 3 3
transition state.
854
dx.doi.org/10.1021/jp209596p |J. Phys. Chem. A 2012, 116, 846–854