ION NEUTRAL COMPLEXES FROM PROTONATED PROPYL PHENYL ETHERS - GAS-PHASE SOLVOLYSIS VERSUS ELIMINATION READDITION

Ion-neutral complexes, well attested as intermediates in the expulsion of alkenes from M+. and MH+ ions from primary alkyl phenyl ethers, are shown to intervene in the decomposition of the MH+ ion of a secondary alkyl phenyl ether, (CD3)2CHOPh. Chemical ionization (CI) (methane reagent gas)-mass-analysed ion kinetic energy spectroscopy (MIKES) shows ions of both m/z 96 and 97, indicating that the proton deposited by the CI reagent exchanges with the methyl deuterium atoms. The ratio of daughter ion intensities, as well as the proportions of ions of m/z 95, 96 and 97 from the MH+ of CD3CH2CD2OPh, agree with predictions based on the gas-phase solvolysis mechanism, in which [i-Pr+ PhOH] complexes form from the protonated parent via simple bond heterolysis. An alternative mechanism, elimination-readdition, would proceed via [propene PhOHD+] complexes. This latter mechanism predicts a ratio of daughter ion intensities that is very different from gas-phase solvolysis and which disagrees with experiment. The elimination-readdition pathway is effectively ruled out, while the gas-phase solvolysis mechanism is reinforced.