Diastereomers and Low-Temperature Oxidation

Diastereomers
have historically been ignored when building kinetic
mechanisms for combustion. Low-temperature oxidation kinetics, which
continues to gain interest in both combustion and atmospheric communities,
may be affected by the inclusion of diastereomers in radical chain-branching
pathways. In this work, key intermediates and transition states lacking
stereochemical specification in an existing diethyl ether low-temperature
oxidation mechanism were replaced with their diastereomeric counterparts.
Rate coefficients for reactions involving diastereomers were computed
with ab initio transition state theory master equation calculations.
The presence of diastereomers increased rate coefficients by factors
of 1.2–1.6 across various temperatures and pressures. Ignition
delay simulations incorporating these revised rate coefficients indicate
that the diastereomers enhanced the overall reactivity of the mechanism
by almost 15% and increased the peak ketohydroperoxide concentration
by 30% in the negative temperature coefficient region at combustion-relevant
pressures. These results provide an illustrative indication of the
important role of stereomeric effects in oxidation kinetics.