Yuvarani Sambathkumar
Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India.

Abiram Angamuthu
Department of Physics, Rathinam Technical Campus, Coimbatore, Tamil Nadu, India.

Praveena Gopalan
Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India.

DOI https://doi.org/10.33889/PMSL.2026.5.1.007

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Abstract

Hydrogen abstraction plays a key role in the atmospheric oxidation of aldehydes and halogenated aldehydes. Their reactivity with atmospheric radicals determines the transformation mechanisms and contribution to secondary pollutant formation, which is essential for evaluating their environmental behavior. The primary objective of this study is to benchmark the performance of three density functionals–B3LYP, M06-2X, and ωB97X-D across three basis set combinations (6-311+G(d,p), 6-311++G(d,p) and 6-311++G(2d,2p)) in predicting the non-catalytic H-abstraction reactions of substituted aldehydes (XCHO, where X = CH3, CF3, CCl3, H, F, Cl) in the presence of methyl radical (C ̇H3). The rate constants were computed using conventional transition state theory (TST) with Eckart tunnelling effect over a temperature range of 300-1700 K. The accuracy of each functional is evaluated by comparing the reaction energies, transition states, thermochemical properties and rate constants obtained in both gas and water-mediated environments with the available experimental and high-level theoretical data. The meta-hybrid GGA functional, M06-2X with better electron correlation and electron density localization effects consistently outperformed others in predicting the barrier energies, reaction enthalpies and rate constants. Also, in addition to M06-2X, the range-separated (RS) hybrid GGA functional ωB97X-D showed reasonable accuracy for rate constants at elevated temperatures (1300-1700 K), while B3LYP underestimated barrier energies and overestimated the rate constants. Among the chosen aldehydes, the aldehydic H-abstraction of ClCHO and CH3CHO exhibited the most favourable paths, while FCHO and H-abstraction from methyl site of CH3CHO took least favourable routes across the temperature range. The benchmarking of the considered H-abstraction reactions in general highlights the interplay between the choice of functionals, basis-sets and substituent-driven electronic effects in predicting reaction barriers and rate constants.

Keywords- DFT functionals, H-abstraction reaction, Aldehydes and halogenated aldehydes, Methyl radical, Rate coefficients, Transition state theory, Temperature-dependent kinetics.

Citation

Sambathkumar, Y., Angamuthu, A., & Gopalan, P. (2026). Non-Catalytic Hydrogen Abstraction Kinetics of Aldehyde–Methyl Radical Reactions: A DFT Benchmark Perspective. Prabha Materials Science Letters, (1), 123-158. https://doi.org/10.33889/PMSL.2026.5.1.007.