Site Selectivity In the Gas-phase Ionic Phenylation of Alcohols and Alkyl Chlorides

Free, unsolvated phenylium ions formed by the spontaneous β decay of [1,4-3H2]benzene were allowed to react with gaseous ROH (R = Et, CF3CH2, Pr, Me2CH; partial pressure 3-56 Torr) or R1Cl (R1 = Pr, Me2CH Bu; partial pressure 20-450 Torr), in the presence of a thermal radical scavenger (O2; 4 Torr). Phenylium ion showed a distinct preference toward the n-center of the substrate (46-100%), although significant insertion into the alkyl group of alcs. was obsd. as well. Phenylium ion displayed significant positional selectivity even between different n-type sites in a bidentate mol. such as CF3CH2OH. An affinity F < O < Cl trend was obsd., which indicated a direct relation between the polarizability of the n-center of the mol. and its orienting properties toward phenylium ions. The stability features of the ionic intermediates from addn. of phenylium ions with ROH or R1Cl have been evaluated, as well as their fragmentation and isomerization mechanisms. The behavior of phenylium ion toward the selected substrates in the gas phase was compared with previous mechanistic hypotheses from related nuclear-decay studies.