ION-MOLECULE REACTIONS IN THE GAS-PHASE .22. REACTIVITY OF THE CIS-INDANEDIOL AND TRANS-INDANEDIOL WITH DIMETHYL ETHER IONS

Specific reactivity of cis-and trans-indanediols has been investigated under dimethyl ether (DME) chemical ionization conditions. Several un usual species, such as [M +29](+) and [M + 27](+) ions, are produced i n high yield. From DME pressure variations and tandem mass spectrometr y experiments (low-energy collisions with Ar and NH,) including some l abeled compounds, it appears that [M + 29](+) ions are generated by nu cleophilic substitution according to a S(N)i pathway from the proton b ound [M + DMEH](+) adduct ion. On the other hand, [M + 27](+) ions are produced from the covalent [M + DME - H](+) adduct ions via a stepwis e process inducing a water loss. This latter dehydration occurs from t he adducts prepared by [DME - H](+) attachment to the homobenzylic hyd roxy site, which allows internal proton transfer from the charged posi tion to the benzylic hydroxy group, promoting the loss of water. In ad dition, trans indanediol labeled with O-18 has been used to obtain evi dence for the regioselectivity of both water-loss mechanisms from the benzylic site. (C) 1997 American Society for Mass Spectrometry.