The Strain Energy of Diphenylcyclopropenone: A Reexamination

Document Type

Article

Publication Date

1-1-1983

Abstract

The published value for A/ff'(g) of diphenylcyclopropenone and its attendant strain energy have been reinvestigated. Conceptual and calculational schemes indicate that the published value is too high by as much as 50 kcal/mol. Preliminary heat of combustion studies support this conclusion. On the basis of isodesmic equations employing the 4-31G and 6-31G* basis sets, significant aromatic stabilization is found in cyclopropenoneAbsolute rates of reaction of ozone with a series of alkenes bearing electron-withdrawing groups have been determined at several temperatures in CC14 by a stopped-flow technique. From these data, activation parameters have been calculated and range from those of tetrachloroethylene (Ea = 11 kcal/mol; log A(s_) = 6.0) to those of styrene (Ea = 3.1 kcal/mol; log A(s-1) = 7.5) and 1-hexene ('a = 2.4 kcal/mol; log A(s 1) = 6.8). These results show that the ozonation of alkenes is quite sensitive to electronic effects, with electron-deficient alkenes reacting orders of magnitude slower than electron-rich alkenes. The rate of reaction of trans-1,2-dichloroethylene is about 25 times that of the cis or the 1,1 isomer, which is consistent with a 1,3-dipolar cycloaddition mechanism. Calculated entropies of activation also are consistent with this, but a general trend toward less negative entropies of activation with lower 'a suggests the possibility of a change in mechanism for more electron-rich alkenes. © 1983, American Chemical Society. All rights reserved.

Identifier

0020845059 (Scopus)

Publication Title

Journal of the American Chemical Society

External Full Text Location

https://doi.org/10.1021/ja00361a018

e-ISSN

15205126

ISSN

00027863

First Page

6855

Last Page

6858

Issue

23

Volume

105

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