Intermolecular dehydration reactions of protonated alkenol adducts

Collisionally activated intermolecular dehydration reactions of proton‐bound alkenol dimers and proton‐bound alkenol‐dimethyl ether adducts were examined in both a triple quadrupole mass spectrometer and a quadrupole ion trap mass spectrometer. Ion‐molecule reactions of profonated dimethyl ether (DME) with allyl alcohol, 3‐buten‐1‐ol and 4‐penten‐l‐ol (M) produced the ions [M + H] + , [2M + H] + , [M + H + DME] + and [M + H + DME − H 2 O] + . Collisionally activated dissociation was used to characterize the structures of the product ions, and energy‐minimized structures and heats of formation of ions were calculated by molecular mechanics and semiempirical computational methods. The loosely bound [M + H + DME] + ions rearrange and dissociate by an intermolecular dehydration reaction to form [M + H + DME ‐ H 2 O] + ions, with methylated ether stuctures. These [M + H + DME − H 2 O] + ions dissociate predominantly via direct cleavage of the ether linkage. Comparisons of the bimolecular and dissociation reactions of the alkenols were made with those of simple alcohols, diols and alkenes to demonstrate that the presence of the carbon‐carbon double bond specifically assists in many of the observed processes.