A comparison of methods for measuring relative radical stabilities of carbon-centred radicals

This article discusses and compares various methods for defining and measuring radical stability, including the familiar radical stabilization energy (RSE), along with some lesser-known alternatives based on corrected carbon–carbon bond energies, and more direct measures of the extent of radical delocalisation. As part of this work, a large set of R–H, R–CH3, R–Cl and R–R BDEs (R˙ = ˙CH2X, ˙CH(CH3)X, ˙C(CH3)2X and X = H, BH2, CH3, NH2, OH, F, SiH3, PH2, SH, Cl, Br, N(CH3)2, NHCH3, NHCHO, NHCOCH3, NO2, OCF3, OCH2CH3, OCH3, OCHO, OCOCH3, Si(CH3)3, P(CH3)2, SC(CH3)2CN, SCH2COOCH3, SCH2COOCH3, SCH2Ph, SCH3, SO2CH3, S(O)CH3, Ph, C6H4–pCN, C6H4–pNO2, C6H4–pOCH3, C6H4–pOH, CF2CF3, CF2H, CF3, CCl2H, CCl3, CH2Cl, CH2F, CH2OH, CH2Ph, cyclo-CH(CH2)2, CH2CHCH2, CH2CH3, CH(CH3)2, C(CH3)3, CCH, CHCH2, CHCHCH3, CHO, CN, COCH3, CON(CH2CH3)2, CONH2, CONHCH3, COOC(CH3)3, COOCH2CH3, COOCH3, COOH, COPh), and associated radical stability values are calculated using the high-level ab initio molecular orbital theory method G3(MP2)-RAD. These are used to compare the alternative radical stability schemes and illustrate principal structure–reactivity trends.