Estimation of steric hindrances at the dimerization of free organic radicals

Томилин, О. Б.; Tanaseichuk, B. S.; Boyarkina, O. V.

doi:10.1134/s1070428016110051

Cited by 7 publications

(4 citation statements)

References 35 publications

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“…As such, the nitroxide radical's half-life depends on the stability of the corresponding hydroxylamine. In addition, protonation of the heterocycle on the nitrogen atom of the hydroxylamine stabilises the molecule [22] while also destabilising the nitroxide radical. Thus, in the case of a structure bearing an electron-withdrawing group (e.g., OH) with a small atomic charge on the N 2 atom, the reduction reaction by ascorbic acid is limited.…”

Section: Sift Deskmentioning

confidence: 99%

“…However, in many cases, calculations into steric factors are based on the limitations of applicable systems, and the calculation methods are complicated. To address these issues, Tomilin and co-workers developed a method combining versatility and convenience that quantifies the degree of steric shielding from the number of atoms contained in a ball, and applied it to predict the reaction point in the radical dimerisation process [22]. However, it seems that such evaluation based on the number of atoms is inaccurate.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Structural and electronic factors relating to the stability of imidazolidine nitroxide radicals

Gotoh¹,

Naganuma²,

Nitta³

et al. 2020

SDRP-JCCMM

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Section: Sift Deskmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structural and electronic factors relating to the stability of imidazolidine nitroxide radicals

Gotoh¹,

Naganuma²,

Nitta³

et al. 2020

SDRP-JCCMM

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“…Tolman et al evaluated steric hindrance in phosphorus ligands of metal complexes using the Tolman cone angle, which is the angle at the top of the cone circumscribed to the ligand [15]. Hirota et al considered a virtual sphere centered on the reaction point of a radical and calculated the number of atoms inside the sphere [17]. Cavallo et al used the volume occupied by atoms in the sphere to evaluate steric hindrance [18].…”

Section: Introductionmentioning

confidence: 99%

Quantification of steric hindrance by geometric calculation, prediction of the reductive selectivity of ketones, and clarification of reaction mechanism

Sakaguchi

Gotoh

2022

Preprint

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Stereoisomers often have different physiological characteristics, and stereocontrol , which includes diastereoselective reduction of carbonyls, is important in the synthesis of pharmaceuticals and natural products. Here, we have developed a model that offers features that have been difficult to achieve simultaneously using conventional methods: reflective of the experimental values of selectivity, applicable to both chained and cyclic ketones, and can quantitatively predict diastereoreductive selectivity. The method, named Moving Sphere Model (MSM), predicts diastereoreductive selectivity by quantifying steric hindrance by the overlapping volume of ketone substrate atoms and a virtual sphere moving in both reaction directions. The reaction mechanism was predicted by examining how the consistency between the calculated selectivity by MSM and the experimental values of selectivity changes when the values of the radius r of the virtual sphere and reaction direction θ are changed. Thus, a reaction mechanism in which only hydride contributes to steric hindrance was inferred for the reduction of ketones by NaBH4 in MeOH solvent. Meanwhile, for the reduction of ketones with NaBH4 in iPrOH solvent, a reaction mechanism in which the solvent introduced to the reducing agent also contributes to steric hindrance was inferred. The MSM enabled us to calculate the angle of nucleophilic attack to carbonyls based on experimental facts, to infer the reaction mechanism of the reduction of ketones with NaBH4 in alcohol solvents, and to predict the reduction selectivity of ketones with NaBH4 in MeOH solvents.

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“…Tomilin et al . used a phantom sphere to assess the steric hindrance of radical species 28 . In their work, the populations of atoms contained in a sphere centered on the reaction centers of carbon, nitrogen, and oxygen radicals were used to calculate a new steric hindrance parameter γ in an effort to analyze radical dimerization reactions.…”

Section: Introductionmentioning

confidence: 99%

A theoretical, dynamical evaluation method of the steric hindrance in nitroxide radicals using transition states of model reactions

Yamazaki

Naganuma

Gotoh

2019

Sci Rep

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Steric hindrance is known to affect the stability, reactivity, and radical trapping ability of stable nitroxide radicals. Therefore, a quantitative evaluation and prediction model of steric hindrance is needed to select and design the optimum nitroxide radicals for specific applications. In this study, a dynamic parameter of steric hindrance (DPSH) is proposed and its characteristics are investigated. Unlike using only the equilibrium structure to evaluate the steric hindrance, DPSH is a dynamic value calculated from the theoretical activation enthalpies for two model reactions of radical addition to olefins. Using DPSH, the steric hindrance was evaluated for a total of 43 alkyl radicals, nitroxide radicals, and radicals derived from phenols, and the results were compared with those of other methods. The DPSH values for radicals can vary when the energy barrier for structural change varies, even if the equilibrium structures of the radicals have the same steric shielding. Finally, for radicals other than nitroxide radicals, the DPSH values were consistent with the predictions from their structures, which suggests that the DPSH has a wide range of applications. We expect DPSH to be used and developed in the analysis of steric factors in various reactions.

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Estimation of steric hindrances at the dimerization of free organic radicals

Cited by 7 publications

References 35 publications

Structural and electronic factors relating to the stability of imidazolidine nitroxide radicals

Structural and electronic factors relating to the stability of imidazolidine nitroxide radicals

Quantification of steric hindrance by geometric calculation, prediction of the reductive selectivity of ketones, and clarification of reaction mechanism

A theoretical, dynamical evaluation method of the steric hindrance in nitroxide radicals using transition states of model reactions

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