  Polariton chemistry has emerged as an appealing branch of synthetic chemistry
that promises mode selectivity and a cleaner approach to kinetic control. Of
particular interest are the numerous experiments in which reactivity has been
modified by virtue of performing the reaction inside infrared optical
microcavities in the absence of optical pumping; this effort is known as
"vibropolaritonic chemistry." The optimal conditions for these observations are
(1) resonance between cavity and reactive modes at normal incidence ($k=0$),
and (2) monotonic increase of the effect with the concentration of emitters in
the sample. Importantly, vibropolaritonic chemistry has only been
experimentally demonstrated in the so-called "collective" strong coupling
regime, where there is a macroscopic number of molecules (rather than a single
molecule) coupled to each photon mode of the microcavity. Strikingly, efforts
to understand this phenomenon from a conceptual standpoint have encountered
several roadblocks and no single, unifying theory has surfaced thus far. This
perspective documents the most relevant approaches taken by theorists, laying
out the contributions and unresolved challenges from each work. We expect this
manuscript to not only serve as a primer for experimentalists and theorists
alike, but also inform future endeavors in the quest for the ultimate formalism
of vibropolaritonic chemical kinetics.
