- http://www.cache.fujitsu.com/mopac/Mopac2002manual/node650.html
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Oxirenes: Lewars E (2000) Can J Chem 78:297–306
96.H 2 C=CHOH reactionThe only quantitative information on the barrier for this reaction
seems to be: Saito S (1976) Chem Phys Lett, 42:399, halflife in the gas phase in a Pyrex
flask at room temperature ca. 30 minutes. From this one calculates (section 5.5.2.2d, Eq
(5.202)) a free energy of activation of 93 kJ mol"^1. Since isomerization may be catalyzed by
the walls of the flask, the purely concerted reaction may have a much higher barrier. This
paper also shows by microwave spectroscopy that ethenol has the O-H bondsynto the C=C.
The most reliable measurement of the ethenol/ethanal equilibrium constant, by flash photol-
ysis, is 5.89- 10 "^7 in water at room temperature (Chiang Y, Hojatti M, Keeffe JR, Kresge
AK, Schepp NP, Wirz J (1987) J Am Chem Soc 109:4000). This gives a free energy of
equilibrium of 36 kJ mol"^1 (ethanal 36 kJ mol"^1 below ethenol). The accurate G3MP2
method [section 5.5.2.2b] places the gas phase free energy of ethanal 43 kJ mol"^1 below that
of ethenol.
HNC reactionThe barrier for rearrangement of HNC to HCN has apparently never been
actually measured. The equilibrium constant in the gas phase at room temperature was
calculated (Maki AG, Sams RL (1981) J Chem Phys 75:4178) at 3.7 x 10"^8 , from actual
measurements at higher 9 temperatures; this gives a free energy of equilibrium of 42 kJ
mol"^1 (HCN 42 kJ mol"^1 below HNC). The G3MP2 method places the gas phase free energy
of HCN 59 kJ mol"^1 below that of HNC.
CH 3 NC reactionThe reported experimental activation energy is 161 kJ mol"^1 (Wang D,
Qian X, Peng J (1996) Chem Phys Lett 258:149; Bowman JM, Gazy B, Bentley JA, Lee TJ,
Dateo CE (1993) J Chem Phys 99:308; Rabinovitch BS, Gilderson PW (1965) J Am Chem
Soc 87:158; Schneider FW, Rabinovitch BS (1962) J Am Chem Soc 84:4215). The energy
difference between CH 3 NC and CH 3 CN has apparently never been actually measured. The
G3MP2 method places the gas phase free energy of CH 3 CN 99 kJ mol"^1 below that of
CH 3 NC.
Cyclopropylidene reactionNeither the barrier nor the equilibrium constant for the cyclopro-
pylidene/allene reaction have been measured. The only direct experimental information of
these species come from the failure to observe cyclopropylidene at 77 K (Chapman OL
(1974) Pure and Applied Chemistry 40:511). This and other experiments (references in
Bettinger HF, Schleyer PvR, Schreiner PR, Schaefer HF (1997) J Org Chem 62:9267 and
in Bettinger HF, Schreiner PR, Schleyer PvR, Schaefer HF (1996) J Phys Chem 100:16147)
show that the carbene is much higher in energy than allene and rearranges very rapidly to the
References 441