Evaluation method of steric shielding effect around nitroxide radical reaction center based on molecular volume within a virtual ball

Steric shielding affects the stability of various molecules such as nitroxide radicals, which have many applications in a variety of fields. Thus, the mechanisms that maintain molecular stability are of particular interest. A new method for nitroxide radicals to quantify the steric shielding effect around the reaction center in a molecule was developed. The steric hindrance in this method is defined as the volume of the molecules contained within a virtual ball centered on the radical atom. With the proposed method, it is possible to evaluate the influences of the β-substituent, the basic molecular skeleton, and other parameters on steric hindrance, which cannot be calculated with E_s^c, a known parameter that indicates bulkiness. This method can acquire more accurate data that more closely resembles the behavior of the actual molecule. Because this method is very simple in that it requires only the optimal stable structure of the molecule, it can be used to estimate the steric shielding of various nitroxide radicals as well as other molecules.