Kinetics vs Thermodynamic Factors in α-Hydrogen Atom Abstraction from Alkyl Aromatics

Article abstract of DOI:10.1021/jo00304a029

The relative reactivities of several 9-alkylanthracenes toward bromine atom have been determined.Whereas for alkylbenzenes it is observed that isopropyl > ethyl > methyl, an inverted reactivity order was observed in the 9-anthryl system: methyl (1.00) > cyclopropyl (0.33) > ethyl (0.063) >> isopropyl (< 0.001), per α-hydrogen at 80 deg C.Stereoelectronic factors, specifically the alignment of the α-C-H bond with the anthryl ?-system, are implicated as bearing primary responsibility for this unusual reactivity order.In a general context, the relative importance of stereoelectronic effects vs the stability of the incipient radical in hydrogen atom abstraction from alkyl aromatics is discussed.