Reactions of the β‐distonic ion ⁺CH₂OCH₂CH₂˙ with butyronitrile: Evidence for an intermediate three‐body ion‐neutral complex during deprotonation

Abstract

Reactions of the j3-Distonic Ion +CH,OCH,CH,' with Butyronitrile: Evidence for an Intermediate Three-body Ion-Neutral Complex during DeprotonationDistonic ions are reactive intermediates of organic gas-phase reactions exhibiting very interesting properties.' In a previous publication2 we discussed the unimolecular and bimolecular reactions of the B-distonic ion +CH20CH,CH2* (a). Using the deuterated ions +CH,0CD2CD; (b) and fCD20CH2CH,' (c), it was shown that a transfers a C2HZ' unit and a CHO' unit to acetonitrile and pyridine, respectively, without any H/D scrambling, corroborating in the case of the C2HZ' transfer earlier observations of Baumann et al. ' The structural integrity of +CH20CH2CH2' revealed by these reactions is attributed to the unique thermodynamic stability of B-distonic ions., However, a second abundant reaction of a is the transfer of a proton to acetonitrile and pyridine, respectively; and from b as well as from c H+-and D+-transfer is observed. Obviously, each of the hydrogen atoms of a is transferred with a certain probability. This may be due either to parallel proton transfers from each of the different positions of a or a H/D scrambling in a prior to the proton transfer, the latter explanation being in conflict with the strutural integrity of a in the other ion-molecule reactions. Both possibilities can be distinguished by a quantitative analysis of H-and D-transfer from the isotopomers b and c, because only in the case of a H/D scrambling (unit preference factor for all positions) are the experimental data described by a single isotope effect k J k D . However, we did not succeed in obtaining consistent quantitative data for the reaction of b and c with CH,CN because the intensity ratio [CH3CNH+]/[CH3CND+] increased continuously with the reaction time. It is very likely that the ion mixture in CH,CN contained some unknown impurities which we were not able to remove. Here we report the results for the reaction of a with n-butyronitrile showing that a indeed loses its structure prior to the transfer of a proton.The B-distonic ion a was generated by electron-impact induced fragmentation of 1,4-dioxane, in the external ion source of a Spectrospin CMS 47X Fourier transform-ion cyclotron resonance (FT-ICR) spectrometer. The resulting ions were transferred into the ICR cell filled with n-C,H,CN at a pressure of 4 x lo-' mbar. In order to study the reactions of b and c, 2,2,3,3-tetradeutero-1,2-dioxane was ionized in the external ion s o u~c e .~*~ The ions a, b and c, respectively, were isolated by removing all other ions using broad-band ejection and specific rf-pulses of low amplitude (' soft single shots') in the mass range of a, b and c. The isolated ions were thermalized by collisions with the reagent gas for 1.5 s, and any ions formed besides those to be studied were again ejected by single shots. Subsequently, mass spectra were obtained at intervals of 0.5 s during a total reaction time of ca. 5 s.

Ion–neutral–neutral complexes in unimolecular reactions: formation of proton-bound alkanol pairs from alkoxylated oxonium ions

“…For example, tert-butyl alcohol so paired with another alcohol, ROH, loses water via an intermediate in which the tert-butyl cation is associated with H 2 O and ROH on each side. 6 The ion-neutral complexes involved in the reactions of those proton-bound pairs are similar to that observed in ionmolecule reactions, 7 where the ion dissociates to generate a new ion-neutral pair while maintaining its coordination with the neutral reactant. In the unimolecular reactions of covalentlybonded organic ions however, intermediate ion-neutral complexes in which an ion (other than a proton) is associated with two neutral molecules have not been reported.…”