Abstract:
Alkenes are one of the major components of hydrocarbons in our atmosphere.
One of the most common alkenes in our atmosphere is isoprene (2-methyl – 1,3 –
butadiene). Currently, it is known that isoprene ozonolysis can lead to the production of
Criegee intermediates CH2OO, methacrolein (MACR) oxide, and methyl vinyl ketone
(MVK) oxide. In part, we were interested in studying one specific Criegee intermediate,
MACR oxide. The competition between the isomerization reactions and the unimolecular
reactions became the focus of our study. Rate constants for the relevant reactions were
calculated by implementing RRKM theory and using Master Equation modeling to create
a scheme for the system. The overall results show that the most favorable reaction of
MACR oxide is the isomerization between the cis and trans conformations. Because the
transition states between these conformations are relatively low compared to the other
transition states in the reaction, the conversions are observed to happen much faster than
the others. The next fastest reaction that takes place is the unimolecular decay reactions
to the dioxiranes and the dioxole. The decay reactions involved barriers that were higher
than the cis⇌trans conversion but still lower than the barrier between the anti⇌syn
conversion. With dioxole being our most stable state, our main interest was if different
conformers of MACR oxide will decay to this structure in an atmospherically relevant
time frame. It was found that substantial fraction (80%) of MACR oxide cannot
decompose to dioxole in the relevant time frame as the barrier for the conversion between
anti and syn is too high. We saw that there was almost no anti⇌syn conversion in any of
our calculations.
