Conformational effects in the identification and quantification of ketohydroperoxides in the oxidation of n-pentane

Abstract

Stereochemistry plays a key role in both fundamental chemical processes and dynamics of a large set of molecular systems of importance in chemistry, medicine and biology. Predicting the chemical transformations of organic precursors in such environments requires detailed kinetic models based on laboratory data. Reactive intermediates play a critical role in constraining the models but their identification and especially their quantification remain challenging. This work demonstrates, via the study of the gas-phase autoxidation of n-pentane, a typical fuel surrogate, that accounting for spatial orientation is essential for accurate characterization of such intermediates and for their further evolution. Using synchrotron-based photoelectron photoion coincidence spectroscopy and high-level quantum calculations to investigate the electronic structure and ionization dynamics of the main ketohydroperoxide isomer formed during the oxidation of n-pentane, we reveal the multiple thermally accessible conformers of the chain-branching agent, highlighting how their distinct ionization energies and fragmentation pathways can significantly affect intermediate quantification via photoionization-based probes, a universal in situ method of choice. This research underscores the importance of stereochemistry not only in combustion systems but in any chemical system where a molecular-level understanding is crucial for developing accurate predictive models for both scientific and industrial applications.