A terbody complex intermediate in [alkyl ether…︁\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm H}\limits^ + $\end{document}…︁alcohol] ions

Abstract

Ions of the form [alkyl ether. ..alcohol] have been generated in the ion-source of a VG ZAB 2F mass spectrometer and studied in the 2nd field-free region. The metastable ions only give the protonated alkyl ether fragment if there is no tertiary carbon in the a position of the oxygen atoms. If there is a tertiary carbon, the formation of protonated ether competes with other processes involving the elongation of the O-C, (tertiary) bond(s). With tertiary alcohols and nontertiary ethers, this elongation leads to a terbody complex in which the tertiary carbocation is solvated by the ether and a molecule of water or, if the ether contains one tertiary group, a terbody complex is formed where the tertiary carbocation is solvated by two molecules of alcohol. Furthermore, a permutation between tertiary groups is observed when both ether and initial alcohol bear such substituents. Most probably, the formation of terbody complexes competes with other mechanisms, concerted processes, for instance.Proton-bound dimers [ROH. . .ha . -HOR] have been investigated under ion cyclotron resonance (ICR) conditions'-2 with the "EB flow" method3 and by chemical ionization (CI) mass spectrometry."6With the CI method, it has been shown that such metastable ions not only lead to the formation of [RbH,] ions but also to losses of water and of alkene when R is a secondary or a tertiary group. Moreover, the study of kinetic energy releases shows that the ratedetermining step of these last fragmentations is the elongation of the bond leading to a complex (a, Scheme 1).of the a complex into the / 3 complex is irreversible (Scheme 1): the 1-2 elimination in the isopropanol moiety is selective.In this work, the fragmentations of alcohol protonbound complexes have been compared with those of [R,RzO-* -He --OHR3] ions. These ions have been generated in the ion-source under CI conditions by reaction of ethers RI-O-R2 with alcohols R30H. These ions have been studied in the 2nd field free region (FFR) of a ZAB 2F mass spectrometer, manufactured by V. G. Analytical Ltd, Manchester UK. RESULTS AND DISCUSSIONThe fragmentations of [R1R20.. . f i e -.0HR3] ions depend on the primary, secondary or tertiary character of the R,, RZ, R3 groups. R,, R, and R3 not tertiary alkyl groupsIn ions 1 and 2, the lone fragment observed in the mass-analysed ion kinetic energy (MIKE) spectra is the initial protonated ether (Scheme 2): an 0-C, bond is never broken. Scheme 1These fragmentations have also been compared with those of protonated ethers R-bH- R7-9 in which the reversible isomerization between a complexes R+ ,