GAS-PHASE NEGATIVE-ION CHEMISTRY OF MOLECULAR FLUORINE - SYNTHESIS OFDISTONIC RADICAL-ANIONS AND RELATED SPECIES

The gas-phase negative ion chemistry of molecular fluorine is describe d, with an emphasis on its use in the regiospecific synthesis of disto nic radical anions and related species. Sequential reaction of organic compounds containing two trimethylsilyl (TMS) substituents with F- fo llowed by F-2 produces distonic radical anions with the negatively cha rged and odd-spin sites determined by the locations of the TMS groups. The mechanism of the F-2 reaction involves dissociative electron tran sfer from the TMS-substituted carbanion to F-2 yielding an F-/radical complex; subsequent attack by F- on the TMS group of the radical produ ces the distonic radical anion product. Experimental evidence in suppo rt of the proposed mechanism is presented, including the dependence of the efficiency of radical anion formation on both the electron bindin g energy of the reactant carbanion and the leaving-group ability of th e radical anion product. Selected applications of the F-2 method for d istonic anion synthesis are described, including formation of the nega tive ions of trimethylene methane, the benzynes, oxyallyl and acetoxyl biradicals and alpha,3-dehydrotoluene. Mechanistic variations in the F-2 reactions with carbanions are described in which the transient F- ion produced by dissociative electron transfer to F-2 reacts with the organic radical in the long-lived complex by proton transfer, nucleoph ilic substitution at carbon, and elimination. Formation of distonic bi radical anions (ionized triradicals) from neutral precursors containin g three TMS groups is described, along with the rational gas-phase syn thesis using F-2 of distonic carbene and nitrene anions. (Int J Mass S pectrom 179/180 (1998) 173-183) (C) 1998 Elsevier Science B.V.