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 <i>α</i>-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.

醛类是烃类燃料燃烧反应中的常见中间体。面向未来氢混合燃烧战略，开展醛类与氢原子的反应动力学研究至关重要。本研究选取两种典型支链醛：2-甲基-1-丁醛（2-methyl-1-butanal，2M1Bal）与3-甲基-1-丁醛（3-methyl-1-butanal，3M1Bal），旨在阐明支链醛与氢原子的夺氢反应动力学机制。采用CCSD(T)/CBS//M06-2X(D3)/def2-TZVP方法，计算得到了两种醛的势能面（Potential Energy Surfaces，PESs）。在300~2000 K温度区间及高压极限（High-Pressure Limit，HPL）条件下，本研究计算了两种醛与氢原子反应的速率常数。结果表明，两种支链C5醛的反应速率常数较为接近。但3M1Bal分子中的醛基官能团会削弱相邻氢原子的C-H键强度，加速该反应位点的夺氢反应。而在2M1Bal与氢原子的反应体系中，尽管与醛基相连的氢原子被弱化，但相邻α-碳原子上的多个官能团进一步降低了该位点C-H键的解离能。上述差异使得两种醛的夺氢反应动力学特性呈现显著差异。本研究有望为支链醛的夺氢反应动力学研究，以及可靠的燃料燃烧动力学模型（尤其是氢混合燃烧反应体系）的构建提供具有价值的参考。