Quantum chemical calculations for over 200,000 organic radical species and 40,000 associated closed-shell molecules

Abstract

The stabilities of radicals play a central role in determining the thermodynamics and kinetics of many reactions in organic chemistry. In this data descriptor, we provide consistent and validated quantum chemical calculations for over 200,000 organic radical species and 40,000 associated closed-shell molecules containing C, H, N and O atoms. These data consist of optimized 3D geometries, enthalpies, Gibbs free energy, vibrational frequencies, Mulliken charges and spin densities calculated at the M06-2X/def2-TZVP level of theory, which was previously found to have a favorable trade-off between experimental accuracy and computational efficiency. We expect this data to be useful in the further development of machine learning techniques to predict reaction pathways, bond strengths, and other phenomena closely related to organic radical chemistry.

Gas-Phase Rate Coefficient of OH + 1,2-Epoxybutane Determined between 220 and 950 K

“…We note that the C-H bonds are relatively strong directly adjacent to the epoxide ring: 102 and 103 kcal/mol for the tertiary and secondary sites respectively, and the most favourable reaction site is probably the remaining secondary C-H bonds, which possess a BDE of 95.9 kcal/mol. 42,43 Assuming this to be the case and that the curvature that is observed is indeed associated with the formation of a vdW complex, we can hypothesize that such a configuration would lead to a bicylic structure such as this:…”

“…In the case of 2-butanol, for example, the alpha tertiary hydrogen atom is especially weak (92.9 kcal/mol), 42,43 which is estimated to account for 63% of the overall reactivity of the molecule at room temperature. 20 In contrast, the reactivity of the two alpha secondary hydrogen atoms in n-butanol are slightly stronger (93.2 kcal/mol), 42,43 and only account for 28% of the total room temperature rate coefficient on a per hydrogen basis. 20 However, it is acknowledged that negative temperature dependence has been observed experimentally in several other metathesis reactions, notably those of alkyl radicals with hydrogen halides.…”

Gas-phase rate coefficient of OH + cyclohexene oxide measured from 251 to 373 K

“…Low barriers are also observed in certain hydrogen abstraction reactions, especially where weak C-H bonds are present, as is the case of the reaction of OH + formaldehyde [22]. However, given that this is considered to be a hydrogen abstraction mechanism, and accounting for the fact that the presence of the oxirane functionality is calculated to increase bond strength in neighbouring C-H bonds [23], we favour the hypothesis that vdW complexes are enhancing the overall rate coefficient at low temperatures through quantum tunnelling. [9], except for the recent data of El Othmani et al [13].…”

Computational Organometallic Catalysis: Where We Are, Where We Are Going

“…Computational results from QM calculations can be used to generate these required data needed to feed the ML models (quantum‐based ML) [56] . The calculation of over 200,000 organic radical species [57] and over 80,000 organometallic compounds [58] are impressive examples of how DFT methods can be used to generate big data sets. These data sets can be exploited in data‐driven predictive ML models for the discovery of new catalysts and reactions.…”