BOND-DISSOCIATION ENERGIES OF THE ACIDIC H-A BONDS IN HA(CENTER-DOT+) RADICAL CATIONS AND IN HA(CENTER-DOT-) RADICAL-ANIONS IN DMSO SOLUTION

An equation based on a thermodynamic cycle has been used for estimating the bond dissociation energies for the cleavage of the acidic H-A bonds in radical anions to form hydride ions and radicals, i.e., HA(.-) --> H- + A(.) (path d in Scheme 1). Estimates of these BDE(HA.-) values have been made for (a) eighteen 2- and 9-substituted fluorenes, (b) six 4-GC(6)H(4)CHPh(2) triphenylmethanes, and related compounds, (c) eight 9-G-CH2-substituted anthracenes, (d) nine 10-substituted 9-methylanthracenes, and (e) five substituted anilines and related N-H acids. Comparisons of these path d BDE(HA.-) values are made with previously obtained BDE(HA.-) values for cleavage of the acidic H-A bonds in these radical anions to form hydrogen atoms (H-.) and A(-) anions, i.e., HA(.-) --> H-. + A(-) (path c in Scheme 1). Analysis of the results indicates that substituents affect the BDE(HA.-) values so as to (a) increase the BDE(HA.-) values by both paths c and d by stabilizing the initial radical anions, and/or (b) decrease the BDE(HA.-) values for reaction by path c and d by stabilizing the initial radical anions, and/or (b) decrease the BDE(HA.-) values for reaction by path d by stabilizing the radical products. The results indicate that reactions by either path c or path d may be viable, the favored pathway depending on the nature of the substituents.