Vinylcyclopropane and Vinylcyclobutane
J. Phys. Chem. A, Vol. 101, No. 22, 1997 4101
formally analogous vinylcyclobutane to cyclohexene process is
essentially strain free. Other lines of experimentation and
theoretical definitions of geometries and energies for the
transition structures associated with these isomerizations will
be required before this kinetically and thermochemically based
inference may be properly tested.
Acknowledgment. This work was supported at Colgate
University by grants from the National Science Foundation
(Grants CHE 9023319 and CHE 9320501), the Howard Hughes
Medical Institute, and the Petroleum Research Fund, adminis-
tered by the American Chemical Society, and at Syracuse
University by the National Science Foundation (Grants CHE
9100246 and CHE 9532016). B.L.K. also thanks Hollins
College for partial support.
References and Notes
(1) Vogel, E. Angew. Chem. 1960, 72, 4-26, note 162. See also:
Overberger, C. G.; Borchert, A. E. J. Am. Chem. Soc. 1960, 82, 1007-
1008.
Figure 6. Thermochemical analysis of ∆Hfo of transition state for
vinylcyclopropane T cyclopentene interconversion. See text for
explanation of values.
(2) Flowers, M. C.; Frey, H. M. J. Chem. Soc. 1961, 3547-3548.
(3) Wellington, C. A. J. Phys. Chem. 1962, 66, 1671-1674.
(4) Retzloff, D. G.; Coull, B. M.; Coull, J. J. Phys. Chem. 1970, 74,
2455-2459.
(5) Lewis, D. K.; Batchelor, P.; Green, W.; Van-Praagh, A.; Kalra, B.
L. Pentadiene Formation during Cyclopentene Pyrolysis. Manuscript in
preparation.
(6) Crane, D. M.; Rose, T. L. J. Phys. Chem. 1975, 79, 403-409 and
references therein.
(7) (a) Farneth, W. E.; Thomsen, M. W.; Berg, M. A. J. Am. Chem.
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(8) Lewis, D. K.; Baldwin, J. E.; Cianciosi, S. J. J. Phys. Chem. 1990,
94, 7464-7467.
That the allyl units of transition structures for vinylcyclo-
propane to cyclopentene rearrangements are substantially twisted
out of planarity has been hypothesized to account for remarkably
large secondary deuterium kinetic isotope effects at the 2′-carbon
of the vinyl group; kH/kD ) 1.17 ( 0.02 at 338 °C for 2′,2′-
d2-labeled vinylcyclopropane, a fact taken as an indication of
torsional distortion.26,27 This interpretation of the kH/kD data
and the different patterns of thermochemical relationships
displayed in Figures 5 and 6 suggest that kH/kD effects for
isomerization of vinylcyclobutane-2′,2′-d2 to cyclohexene-3,3-
d2 will turn out to be far more modest than those seen for
superficially analogous vinylcyclopropane and substituted vi-
nylcyclopropane isomerizations.
(9) Kosnik, K. G.; Benson, S. W. J. Phys. Chem. 1983, 87, 2790-
2795.
(10) Pottinger, R.; Frey, H. M. J. Chem. Soc., Faraday Trans. 1 1978,
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(11) Micka, T. A. The Thermal Unimolecular Reaction Kinetics of
Vinylcyclobutane at Low Pressure. Ph.D. Dissertation, University of Oregon,
1980.
Conclusions
(12) Wellman, R. E.; Walters, W. R. J. Am. Chem. Soc. 1957, 79, 1542-
1546. For the conversion of methylcyclobutane to ethene plus propylene,
the activation parameters are 15.4 and 61.2 kcal/mol (Das, M. N.; Walters,
W. D. Z. Phys. Chem. (Frankfurt/Main) 1958, 15, 22-33).
Accurate rate constants measured over large temperature
ranges provide more reliable Arrhenius parameters than can be
secured from rate constant data obtained over modest temper-
ature ranges. By combining static-reactor-based kinetic data
and shock-tube kinetic results, the present work has essentially
reproduced the Arrhenius activation parameters obtained by
Pottinger and Frey10 and by Micka11 for the thermal fragmenta-
tion and isomerization reactions of vinylcyclobutane at relatively
low temperatures and demonstrated that they give a reliable basis
for calculating rate constants even when applied at much higher
temperatures. This confirmation of Arrhenius parameters for
the reactions vinylcyclobutane f all products, vinylcyclobutane
f ethene + 1,3-butadiene, and vinylcyclobutane f cyclohexene
to within combined experimental uncertainties extends the
temperature range of demonstrated reliability for rate constants
calculated with these parameters. Computer modeling based
on these parameters strengthens the case for a nondirect and
stereochemically nonconservative path leading from cyclohexene
to ethene plus 1,3-butadiene by way of vinylcyclobutane.14 Rate
constants secured for the vinylcyclopropane to cyclopentene
isomerization over a wide temperature range, 577-1054 K,
provided a revised Ea for the isomerization of vinylcyclopropane
to cyclopentene, 51.7 ( 0.5 kcal/mol rather than the Ea ) 49.6-
49.7 kcal/mol reported by earlier investigators. This new Ea
value and thermochemical considerations suggest that the
transition structure for the isomerization has some 4.6 ( 0.9
kcal/mol of strain energy, while the transition structure for the
(13) Tsang, W.; Walker, J. A. J. Phys. Chem. 1992, 96, 8378-8384.
(14) Lewis, D. K.; Brandt, B.; Crockford, L.; Glenar, D. A.; Rauscher,
G.; Rodriguez, J.; Baldwin, J. E. J. Am. Chem. Soc. 1993, 115, 11728-
11734. The fit between model and data was best when it was assumed that
there was no retention of cyclohexene stereochemistry in ethene molecules
formed via vinylcyclobutane; the complete loss of stereochemistry in the
vinylcyclobutane f ethene + 1,3-butadiene reaction has now been
demonstrated experimentally (Lewis, D. K.; Hutchinson, A.; Lever, S. J.;
Spaulding, E. L.; Bonacorsi, S. J., Jr.; Baldwin, J. E. Isr. J. Chem. 1996,
36, 233-238).
(15) Lewis, D. K.; Giesler, S. E.; Brown, M. S. Int. J. Chem. Kinet.
1978, 10, 277-294.
(16) Lewis, D. K.; Bergmann, J.; Manjoney, R.; Paddock, R.; Kalra, B.
L. J. Phys. Chem. 1984, 88, 4112-4116.
(17) Barnard, J. A.; Cocks, A. T.; Lee, R. Y.-K. J. Chem. Soc., Faraday
Trans. 1 1974, 70, 1782-1792. Lewis, D. K.; Feinstein, S. A.; Jeffers, P.
M. J. Chem. Phys. 1977, 81, 1887-1888.
(18) Kalra, B. L.; Afriyie, Y.; Brandt, B.; Lewis, D. K.; Baldwin, J. E.
J. Phys. Chem. 1995, 99, 8142-8146.
(19) Pedley, J. B.; Naylor, R. D.; Kirby, S. P. Thermochemical Data of
Organic Compounds; 2nd ed.; Chapman and Hall: London, 1986.
(20) From ∆Hfo for ethylcyclobutane, -6.3 ( 0.3 kcal/mol,19 and the
assumption that -∆Ho for hydrogenation of vinylcyclobutane is equal to
∆∆Hfo between vinylcyclopropane and ethylcyclopropane, 30.0 ( 0.3 kcal/
mol (Roth, W. R.; Kirmse, W.; Hoffmann, W.; Lennartz, H.-W. Chem.
Ber. 1982, 115, 2508-2515). This value is derived from -∆Ho for
hydrogenation of vinylcyclopropane to n-pentane (∆Hfo ) -35.1 ( 0.2
kcal/mol19), 65.5 ( 0.2 kcal/mol, and ∆Hfo for ethylcyclopropane, +0.4 (
0.2 kcal/mol.19,21 See also: Roth, W. R.; Adamczak, O.; Breuckmann, R.;
Lennartz, H.-W.; Boese, R. Chem. Ber. 1991, 124, 2499-2521.
(21) (a) Chickos, J. S.; Hyman, A. S.; Ladon, L. H.; Liebman, J. F. J.