(608d) Reaction Control of Transient Systems: Identifying the Dominant Transition and Intermediate States

Elucidating the energetics for all of the states in a
complex reaction pathway, and identifying the kinetically feasible mechanisms
for a chemical process is costly and time-consuming.  Many of the
intermediate and transition states along the reaction pathway only weakly
influence the overall net rate; and therefore, a desirable alternative is to
determine the states that have the most influence and precisely calculate their
properties.  An approach that has been proposed to determine the most
influential states is the degree of rate control (C. Stegelmann,
et al., JACS 131, 13563 (2009)).  While most reports
have only studied stationary (steady-state) processes, there are many
applications where the reactions operate in a transient mode.  In this
work a variant of the degree of rate control method is introduced for transient
systems; the differences between the transient and stationary approaches are
highlighted.  The role that an intermediate species' concentration has on
the rate controlling states is discussed and a method to account for the
effects is described.  The transient variation of the degree of rate
control is demonstrated for processes with increasing complexity to show how
using the transient degree of rate control provides important insight into each
system.  The influence of reversibility between intermediate states,
energetic interactions between species in the intermediate states, and how the
approach is used to identify the net activation barrier are also discussed.