We also examined the stability of the DAAN radicals generated when the benzylic hydrogen of the DAAN derivative is abstracted by the mechanoradical. It is generally accepted that the thermodynamic stability from spin delocalization and kinetic stability from steric protection are the two main factors that account for the overall stability of long-lived radicals. On the other hand, the bond-dissociation energy (BDE) is a parameter that is often used to evaluate the thermodynamic stability of radicals. As shown in equation ( ), the BDE is the energy required for cleaving the hydrogen adduct (R-H) of the radical (R•) into R• and H• (Figure ); the smaller this value, the more readily homolysis occurs and the greater the amount of thermodynamically stable radicals generated.