Ion-molecule reactions in the gas phase. part XXII. Reactivity of the cis- and trans-indanediols with dimethyl ether ions

Specific reactivity of cis- and trans-indanediols has been investigated under dimethyl ether (DME) chemical ionization conditions. Several unusual species, such as M + 29]⁺ and M + 27]⁺ ions, are produced in high yield. From DME pressure variations and tandem mass spectrometry experiments (low-energy collisions with Ar and NH₃) including some labeled compounds, it appears that M + 29]⁺ ions are generated by nucleophilic substitution according to a S_Ni pathway from the proton boundM + DMEH]⁺ adduct ion. On the other hand, M + 27]⁺ ions are produced from the covalent M + DME ? H]⁺ adduct ions via a stepwise process inducing a water loss. This latter dehydration occurs from the adducts prepared by DME ? H]⁺ attachment to the homobenzylic hydroxy site, which allows internal proton transfer from the charged position to the benzylic hydroxy group, promotingthe loss of water. In addition, trans indanediol labeled with ¹⁸O has been used to obtain evidence for the regioselectivity of both water-loss mechanisms from the benzylic site.