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 C₃H₇/H₂O]⁺ and C₄H₉/H₂O]⁺ ions generated by the (formal) gas phase addition reactions in a high pressure ion source of s-C₃H₇]⁺ and t-C₄H₉]⁺ ions with the n-donor H₂O. Similarly, s-C₃H₇/CH₃OH]⁺ ions generated by both gas phase protonation of n- and s-propyl methyl ethers and addition reactions of C₃H₇]⁺ to CH₃OH display mode-of-generation-independent collisionally induced dissociation characteristics. However, analysis of the unimolecular dissociation (loss of propene) of the C₃H₇/CH₃OH]⁺ system, including a number of its deuterium, ¹³C- and ¹⁸O-labelled isotopomers, supports the idea that prior to unimolecular dissociation, covalently bound C₃H₇- O(H)CH₃]⁺ ions intercovert with hydrogen-bridged adduct ions, analogous to the behaviour of the distonic ethene-, propene- and ketene-H₂O radical cations.