In the Earth’s
atmosphere, reactive organic carbon undergoes
oxidation via a highly complex, multigeneration process, with implications
for air quality and climate. Decades of experimental and theoretical
studies, primarily on the reactions of hydrocarbons, have led to a
canonical understanding of how gas-phase oxidation of organic compounds
takes place. Recent research has brought to light a number of examples
where the presence of certain functional groups opens up reaction
pathways for key radical intermediates, including alkyl radicals,
alkoxy radicals, and peroxy radicals, that are substantially different
from traditional oxidation mechanisms. These discoveries highlight
the need for methods that systematically explore the chemistry of
complex, functionalized molecules without being prohibitively expensive.
In this work, automated reaction network generation is used as a screening
tool for new pathways in atmospheric oxidation chemistry. The reaction
mechanism generator (RMG) is used to generate reaction networks for
the OH-initiated oxidation of 200 mono- and bifunctionally substituted n-pentanes. The resulting networks are then filtered to
highlight the reactions of key radical intermediates that are fast
enough to compete with traditional atmospheric removal processes as
well as “uncanonical” processes which differ from traditionally
accepted oxidation mechanisms. Several recently reported, uncanonical
atmospheric mechanisms appear in the RMG dataset. These “proof
of concept” results provide confidence in this approach as
a tool in the search for overlooked atmospheric oxidation chemistry.
Several previously unreported reaction types are also encountered
in the dataset. The most potentially atmospherically important of
these is a radical–carbonyl ring-closure reaction that produces
a highly functionalized cyclic alkoxy radical. This pathway is proposed
as a promising target for further study via experiments and more detailed
theoretical calculations. The approach presented herein represents
a new way to efficiently explore atmospheric chemical space and unearth
overlooked reaction steps in atmospheric oxidation.