Theoretical Investigation on the Reaction Mechanism of Two Branched Aldehydes with Hydrogen Atoms: 2- and 3-Methyl-1-Butanal

Aldehydes are common intermediates in the combustion reaction of hydrocarbon fuels. Driving by future hydrogen mixed combustion strategy, studying the reaction kinetics of aldehydes with H atoms is crucial. In this work, two typical branched-chain aldehydes, 2-methyl-1-butanal (2M1Bal) and 3-methyl-1-butanal (3M1Bal), were selected to clarify the H-abstraction reaction kinetics of branched-chain aldehydes by H atom. The potential energy surfaces (PESs) for both aldehydes are obtained using the CCSD(T)/CBS//M06-2X(D3)/def2-TZVP method. The rate constants for H atom with two aldehydes reactions are calculated over 300–2000 K and at high-pressure limit (HPL). In this study, the reaction rate constants of the two branched-chain C5 aldehydes are very close to each other. However, the presence of aldoxy functional groups in 3M1Bal weakened the C-H bond strength of adjacent H atoms and accelerated the H-abstraction reaction at this reaction site. In the reaction between 2M1Bal with H atoms, although the H atom attached to aldehydes is weakened, the presence of multiple functional groups on adjacent α-C atoms further reduces the dissociation energy of the C-H bond at this site. These differences lead to significant variations in the kinetic characteristics of the H-abstraction reactions for the two aldehydes. This study is expected to provide a valuable reference for the H-abstraction kinetics of branched-chain aldehydes and the establishment of a reliable fuel combustion kinetic model, especially the hydrogen mixed combustion reaction system.