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

Abstract

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.

Chemical transformation of <i>α</i>-pinene-derived organosulfate via heterogeneous OH oxidation: implications for sources and environmental fates of atmospheric organosulfates

“…In general, the OH reactivity for the primary carbons (8-C, 9-C, and 11-C) and hydroxyl group (10-O) were predicted to be slower than that of the secondary and tertiary carbons except 5-C. We would like to acknowledge that uncertainties could arise from the fact that the sulfate group (−OSO 3 − ) is currently not being considered in the SAR model and differences between the concentrated aqueous aerosols and the SAR model that is formulated for dilute aqueous solutions. Other factors such as steric hindrance and long-distance electronic effects of the sulfate group (−OSO 3 − ) on the reactivity have not been considered (Yamazaki et al, 2019) and warrant further study.…”

Chemical Transformation of α-Pinene derived Organosulfate via Heterogeneous OH Oxidation: Implications for Sources and Environmental Fates of Atmospheric Organosulfates

“…In general, the OH reactivity for the primary carbons (8-C, 9-C, and 11-C) and hydroxyl group (10-O) were predicted to be slower than that of the secondary and tertiary carbons except 5-C. We would like to acknowledge that uncertainties could arise from that the sulfate group (−OSO3 − ) is currently not being considered in the SAR model and differences between the concentrated aqueous aerosols and 10 the SAR model that is formulated for dilute aqueous solutions. Other factors such as steric hindrance and long-distance electronic effects of the sulfate group (−OSO3 − ) on the reactivity have not been considered (Yamazaki et al, 2019) and are warranted for further studies.…”

Physical Properties of Newly Developed Resin Modified Glass Ionomer Cement with Synthesised Coumarin Derivatives

“…In the fabricated materials of RMGIC with coumarins, possibility of chemical energy that bond between carboxylate group of polyacid and cationic groups of AC is higher than CT. This postulation may due to the bulk structure of CT that can lead to the higher steric effect than AC during the interaction with polyacid of RMGIC and eventually caused steric hindrance (Yamazaki et al 2019). The phenomenon would dictate the reactivity of RMGIC-CT and may reduce the stability of the material, simultaneously reduced the hardness property of the material (Yamazaki et al 2019).…”

“…This postulation may due to the bulk structure of CT that can lead to the higher steric effect than AC during the interaction with polyacid of RMGIC and eventually caused steric hindrance (Yamazaki et al 2019). The phenomenon would dictate the reactivity of RMGIC-CT and may reduce the stability of the material, simultaneously reduced the hardness property of the material (Yamazaki et al 2019). Fabricated RMGIC-coumarins can potentially be used for restoration treatment, and therefore, the hardness property is important due to its resistance to an occlusal load (Tüzüner & Ulusu 2012).…”