A Computational Study of the Reactions of Thiiranes with
Ammonia and Amines
Harold D. Banks
William E. White
10.1021/jo001719s.s003
https://acs.figshare.com/articles/journal_contribution/A_Computational_Study_of_the_Reactions_of_Thiiranes_with_Ammonia_and_Amines/3688035
The relative rates of reaction of thiirane and thiirane derivatives with NH<sub>3</sub>, a series of secondary
amines including aziridine, and trimethylamine were determined in the gas phase by means of
B3LYP/6-31+G(d)//HF/6-31+G(d) computations and transition state theory. Convergence of the
results was selectively tested using the 6-311++G(d,p) basis set. Comparison with MP2/6-31 +
G(d)//MP2/6-31G(d) computations was made in model cases. These results are significant in that
they supplement the only reported gas-phase experimental study of this type of reaction. The
reaction rates of thiirane with secondary amines can best be rationalized by means of an interplay
of steric and polarizability effects. While β-halo substituents retard S<sub>N</sub>2 reactions in solution, both
2-fluorothiirane and its acyclic model react more than l0<sup>6</sup> times faster with NH<sub>3</sub> than the
unsubstituted compounds in the gas phase. 2-Fluorothiirane was calculated to react with NH<sub>3</sub> at
C<sub>2</sub> by a factor of 0.142 with respect to thiirane itself; attack at C<sub>3</sub> was found to be 3.42 × 10<sup>6</sup> times
faster than the parent compound. 2-Methylthirane reacts with NH<sub>3</sub> at 0. 230 the rate of thiirane
with a 12.8-fold regioselectivity for C<sub>3</sub>. In the reaction of 2,2-dimethylthirane and NH<sub>3</sub>, this
preference for C<sub>3</sub> increases to a factor of 124. Ground-state destabilization of <i>cis</i>-2,3-dimethylthiirane
is sufficient to account for its calculated rate acceleration with respect to the trans isomer.
2001-08-10 00:00:00
factor
S N 2 reactions
compound
l 0 6 times
B 3LYP computations
C 3 increases
NH 3
gas phase
MP
amines
transition state theory
C 3
thiirane
model