Study of ion structures produced by the reaction of 2‐propyl cations with water and methanol; covalently bound v. Hydrogen‐bridged adducts

In contrast to an earlier report, 1 the collisonally induced dissociation of protonated 2‐propanol and t ‐butyl alcohol yields spectra that are indistinguishable from those of the corresponding [C 3 H 7 /H 2 O] + and [C 4 H 9 /H 2 O] + ions generated by the (formal) gas phase addition reactions in a high pressure ion source of [ s ‐C 3 H 7 ] + and [ t ‐C 4 H 9 ] + ions with the n ‐donor H 2 O. Similarly, [ s ‐C 3 H 7 /CH 3 OH] + ions generated by both gas phase protonation of n ‐ and s ‐propyl methyl ethers and addition reactions of [C 3 H 7 ] + to CH 3 OH display mode‐of‐generation‐independent collisionally induced dissociation characteristics. However, analysis of the unimolecular dissociation (loss of propene) of the [C 3 H 7 /CH 3 OH] + system, including a number of its deuterium, 13 C‐ and 18 O‐labelled isotopomers, supports the idea that prior to unimolecular dissociation, covalently bound [C 3 H 7 ‐ O(H)CH 3 ] + ions intercovert with hydrogen‐bridged adduct ions, analogous to the behaviour of the distonic ethene‐, propene‐ and ketene‐H 2 O radical cations.