A Detailed Look at the Reaction Mechanisms of Substituted
Carbenes with Water
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Abstract
Two competitive reaction mechanisms
for the gas-phase chemical
transformation of singlet chlorocarbene into chloromethanol in the
presence of one and two water molecules are examined in detail. An
analysis of bond orders and bond order derivatives as well as of properties
of bond critical points in the electron densities along the intrinsic
reaction coordinates (IRCs for intermediates → transition state
(TS) → products) suggests that, from the perspective of bond
breaking/formation, both reactions should be considered to be highly
nonsynchronous, concerted processes. Both transition states are early,
resembling the intermediates, yielding rate constants whose magnitudes
are mostly influenced by structural changes and to a lesser degree
by bond breaking/formation. For the case of one water molecule, most
of the energy in the reactants region of the IRC is used for structural
changes, while the transition state region encompasses the majority
of electron activity, except for the formation of the C–O bond,
which extends well into the products region. In the case of two water
molecules, very little electron flux and comparatively less work required
for structural changes is noticed in the reactants region, leading
to an earlier transition state and therefore to a smaller activation
energy and to a larger rate constant. This, together with evidence
gathered from other sources, allows us to provide plausible explanations
for the observed difference in rate constants