Isomerization of the Molecular Ion of Allyl Bromide

Abstract

The molecular ion of allyl bromide has been characterized by ab initio molecular orbital calculations at the MP4(SDTQ) level with optimized geometries at the MP2 level in order to account for experimental data suggesting the presence of two isomers. The calculations predict the existence of an allyl bromide molecular ion with structural parameters resembling the neutral species except for a lengthening of the double bond. This structure is calculated to be more stable than a cyclic bromonium radical cation structure. Rearrangement of the molecular ion of allyl bromide to that of 1-bromopropene is shown to be possible through a transition state represented by the distonic ion, + BrHCCH 2 CH 2 • , lying just below the dissociation limit of the allyl bromide molecular ion. Studies based on ion/molecule reactivity of C 3 H 5 Br •+ ions generated from allyl bromide and 1-bromopropene with ammonia, methanol, allyl bromide, and charge transfer reactions strongly suggest that a small fraction of the molecular ions of allyl bromide isomerize to the 1-bromopropene molecular ion as predicted by the calculation. These experiments cannot establish unequivocally whether the allyl bromide molecular ions retain the structure of the parent molecules as predicted by the calculations or undergo ion/ molecule reactions mediated by a bromonium type complex. Charge transfer experiments also suggest the adiabatic ionization energy of allyl bromide to be 9.83 ( 0.07 eV.

Ring-Hydrogen Participation in the Keto-Enol Isomerization of the Acetophenone Radical Cation

“…[10,18] The basic experimental procedure was similar to that used in our work on the dissociation of the molecular ions of acetophenone induced by thermal radiation. [10a] Shortly, ions were produced directly in a 15.6 cm 3 cubic cell by electron impact in two different ways: a) pulsing the voltage on the filament from 10 V to the ionizing energy chosen for the particular experiment resulting in 20 to 50 ms ionization pulse (depending on the pressure); b) pulsing the current of the filament for periods of 200 to 400 ms.…”

Gas-phase ion chemistry of silyl cations obtained from hexamethyldisilazane

“…The general characteristics of the spectrometer and its application towards the elucidation of gas-phase ion reaction sequences have been illustrated in a number of publications from these laboratories [23][24][25][26] . This spectrometer typically operates at a fixed magnetic field of 1.0 T provided by a Varian 9 inch electromagnet.…”

Dissociação Unimolecular Induzida por Radiação Térmica".

“…O íon molecular de brometo de alila apresenta a interessante característica de que ao ser produzido por impacto de elétrons sofre um processo de isomerização (MORGON, GIROLDO et al, 1996). São produzidas duas estruturas, com proporção dependente da energia de energia de ionização usada.…”

“…dos íons isolados não dissociam-se. Este número aparentemente alto, por ser maior dos que os 20 % anteriormente observados (MORGON, GIROLDO et al, 1996 fig. 8.4 ).…”