Protonated alkylbenzenes: Hydride abstraction in π complexes

Hydride abstraction from 1,3,5‐cycloheptatriene by gaseous carbenium ions, as studied by Fourier transform ion cyclotron resonance kinetics and deuterium labeling

“…Notably, tert-butyl cations were found to exert kinetic isotope effects in a very narrow range, k(H À )=k(D À ) ¼ 1.6 AE 0.1, in ion-neutral complexes with simple alkylbenzenes and various ,!-diphenylalkanes. [22][23][24][25][26][27][28] The kinetics of the interaction of 1a and protonated acetone [2 þ H] þ and tert-butyl cations [3 þ H] þ are reproduced in Figs 4 and 5, respectively. Table 1.…”

“…The branching ratios allow us to determine the kinetic isotope effects, 29 which again were found to be in the range k(H À )= k(D À ) ¼ 1.6-1.7. This result is in good agreement with those obtained previously for alkylbenzenes and ,!diphenylalkanes [22][23][24][25][26][27][28] and can be considered a further confirmation of the mechanism of the formation of the C 7 H 7 þ ions by competitive hydride transfer from 1. The kinetic results of the proton and hydride transfer reactions between cycloheptatriene and ions [2 þ H] þ and [3 þ H] þ are given in Table 1.…”

Unimolecular reaction mechanisms: the role of reactive intermediates

“…Audier et al [46] of the MIKE spectrum is shown in the small insert of Scheme 20, and it is seen that both C4H10 and C4H9D are lost, the latter requiring a migration of the tert-butyl cation to the remote benzyl group. The MIKE spectrum of the derivative deuterated at the benzylic position next to the 4-tert-butylphenyl group is nearly identical to that shown in Scheme 20.…”

“…Labelling with stable isotopes revealed tttat t~e isobutarte ts ¢omgosed of the ter~-13utyl s{de-chaf,~ and a hydrogen atom from the ~-CH2 of the ethyl group. An estimation of the reaca~on em3oa3~es s)~oweb I~oaI )~o £o)s case e))m)na#on oY t)~e a)~ane is more [46]. The mechanism of the alkane elimination is shown in Scheme 10.…”

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

“…-HOR] have been investigated under ion cyclotron resonance (ICR) conditions'-2 with the "EB flow" method3 and by chemical ionization (CI) mass spectrometry." 6 With 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).…”