475503-68-5Relevant academic research and scientific papers
Unimolecular Reactions of Isolated Organic Ions. The Importance of Ion-Dipole Interaction
Bowen, Richard D.,Williams, Dudley H.
, p. 2752 - 2756 (1980)
Possible mechanisms are discussed for the decomposition of "onium" ions of general formula R1CH=X+CR2R3CHR4R5 (R = H or alkyl; X = O, S, NH, or NCH3).For olefin elimination, to form R1CH=X+H and R2R3C=CR4R5, a simple concerted, "four-center" process can account for a considerable proportion of 2H-labeling results.However, such a mechanism would be symmetry forbidden and may be excluded on orbital symmetry and energetic grounds.A highly nonsynchronous mechanism is proposed, involving the formation of a loose complex of the carbonyl component, R1CH=X, and the carbonium ion, R2R3C+CHR4R5.Extensive stabilization of this intermediate is possible, by ion-dipole attraction; subsequent rearrangement can lead to a second complex, in which the carbonyl component and the incipient olefin are coordinated to a common proton.Isomerization of the nascent olefin fragment may take place, in the second complex, by protonation followed by deprotonation at a different site.Finally, the second complex breakes down, with elimination of an olefin or carbonyl component, the incipient fragment with the greater proton affinity remaining bound to the common proton.
Thermodynamic Studies of Gas-phase Proton Transfer Equilibria involving Benzene: A Reassessment of Earlier Data
Parry, Alyn,Fernandez, M. Tereza,Garley, Mike,Mason, Rod
, p. 3331 - 3338 (2007/10/02)
Temperature-variable equilibrium constant measurements have been performed for a number of proton-transfer equilibria in which benzene was a partner, using a newly built high-pressure pulsed source mass spectometer.Entropy values obtained showed that the protons in protonated benzene are not as mobile as previously thought.Systems involving ethanol are found to give anomalous, though self-consistent results owing to the onset of thermal decomposition.In the light of this, previous data involving halotoluenes and xylenes which appear to show unusually large increases in entropy on protonation, have been reassessed.There is evidence of proton-induced isomerisation.In the reaction H(1+) -> H(1+) the free energy of activation is derived to be ca. 90 kJ mol-1 from a computer model fit to the results, consistent with the energy calculated to be needed for a proton shift from the 3 to the 4 position in the precursor.The equivalent reaction for protonated 4-fluorotoluene has a barrier which is ca. 10 kJ mol-1 higher.A kinetic scheme is presented which shows how this could account for the observed 'thermodymanimc' behaviour, and also give rise to the 'isokinetic effects' previously noted.There has therefore been some readjustment of the recommended proton affinity values for some of these compounds.
