Ter-body intermediates in the gas phase: Reaction of ionized enols with tert-butanol

In the gas phase, the CH2CHOH.+ enol radical cation 1 as well as its higher homologues CH3CHCHOH.+ 2 and (CH3)(2)CCHOH.+ 3, undergo exactly the same s equence of reactions with tert-butanol, leading to the losses of isobutene, water and water plus alkene. Fourier transform ion cyclotron resonance (FT -ICR) experiments using labeled reactants as well as ab initio calculations show that independent pathways can be proposed to explain the observed rea ctivity. For ion 1, taken as the simplest model, the first step of the reac tion is formation of a proton bound complex which gives, by a simple exothe rmic proton transfer, the ter-body intermediate [CH2CHO., H2O, C(CH3)(3)(+) ]. This complex, which was shown to possess a significant lifetime, is the key intermediate which undergoes three reactions. First, it can collapse to yield tert-butylvinyl ether with elimination of water. Second, by a regios pecific proton transfer, this complex can isomerize into three different te r-body complexes formed of water, isobutene and ionized enol. Within one of these complexes, which does not interconvert with the others, elimination of isobutene leads to the formation of a solvated enol ion. Within the othe rs, a cycloaddition-cycloreversion process can proceed to yield the ionized enol 3 (loss of water and ethylene channel). (C) 2001 American Society for Mass Spectrometry.