Seven alkyl substituted methyl cyclopropanecarboxylates
having an alkyl group on C-2 cis to the ester group have been
found to rearrange thermally to their corresponding if, [formula omitted]
esters at temperatures ranging from 240° to 300° . The corresponding
trans isomers are unaffected under identical reaction
conditions. It is proposed that the rearrangement takes place by
an intramolecular 1,5-hydrogen transfer via a six-membered cyclic
transition state. The kinetics for these reactions have been studied
and show first-order plots which are linear to 70% reaction. The
heat of activation [formula omitted]
was found to be between 25 to 38 kcal/
mole and the entropy of activation [formula omitted]
was found to be between
- 8 and -37 eu from measurements made over a 20° range. This
and other information fully support a cyclic hydrogen transfer
mechanism.
Four methyl cis-2-pentenoates have been found to undergo
both geometric and positional thermal isomerizations to yield equilibrium mixtures of
2- and 3-pentenoates at temperatures ranging
from 240° to 300°. The 3-pentenoates produced from the corresponding
trans-2-pentenoates were found to be formed via the cis -
2-pentenoate3. Studies using β-isopropylacrylate and methacrylate
showed that the rate of positional isomerization was much faster than that of geometric
isomerization. For these systems
it was therefore possible to study the kinetics of the positional
isomerism in the absence of competing geometric isomerization,
The kinetic data provided first-order plots. The heat of activation
[formula omitted]
was found to be between 18 and 38 kcal/mole and the
entropy of activation [formula omitted]
was found to be between -8 to -50
eu. An intramolecular 1,5-hydrogen transfer mechanism involving
a six-membered cyclic transition state similar to that for the
cyclopropane series is indicated and is suggested to be the general
mechanism for conversion of [formula omitted] esters to [formula omitted] esters.
The series of 2-alkylcyclopropanes have been prepared by
the decomposition of the corresponding pyrazoline3. Some of these
pyrazolines have been newly synthesized for this work and include [formula omitted]
esters required for this research. Several,
however, have also been synthesized by the modified Wittig reaction. / Science, Faculty of / Chemistry, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/41201 |
| Date | January 1967 |
| Creators | Chiu, Norman Wing Kwai |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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