On the positional interchange of the phenyl- and hydroxyl groups in the [C9H11O]+-ion,generated from 2-methyl-2-phenylpropane-1,3-diol (C10H14O2) upon electron-impact

It is shown by deuterium-labelling experiments, that a substantial part of the [M – CH₂OH]⁺-ions from 2-methyl-2-phenyl-propane-1,3-diol must have rearranged to carbonyl-oxygen protonated phenylacetone by a positional interchange of the phenyl- and hydroxyl groups prior to decomposition.     

Evidence suggesting the occurrence of [2+3] cycloaddition products in the ion/molecule reactions of suitably substituted allyl cations and olefins

The ion/molecule reactions of allyl cations and 2-methoxyallyl cations with vinyl methyl ether, 1-chloro-2-ethoxyethene and 1,2-dimethoxyethene are discussed in terms of [2+3] cycloaddition reactions. Deuterium labelling of the cations has been used for the study of the reaction mechanisms. The appearance of various product ions in these ion/molecule reactions lead to the suggestion that in reactions of allyl cations with alkenes non-cyclic [C₅H₅]⁺ product ions are formed preferentially, but that in reactions of 2-methoxyallyl cations with alkenes a significant part of the product ions are methoxycyclopentadienyl cations. These observations are ascribed to the stabilizing effect of the methoxy group with regard to the positive charge in the product ions.     

An icr study on the structure of the C6H6O+• ion from phenetole

The C₆H₆O^+?ion from phenetole is generated by hydrogen transfer predominantly from the terminal-position, but also to some extent from the position next to oxygen. Deuterium labelling and ion-molecule reactions show that both transfers occur to the oxygen atom and not to the aromatic ring. The C₆H₆O^+?ion is thus formed exclusively in the phenolic structure.     

Chain length effects in the competition between intramolecular hydrogen migrations in the molecular ions of hydrogen migration in the molecular ions of α-benzylamino-ω-benzyloxyalkanes as studied by deuterium labelling

The unimolecular decompositions upon electron impact of the bifunctional compounds ØCH₂-NH? (CH₂)_n-O? CH₂Ø(n=2 to 7)have been studied by deuterium labelling. The molecular ions lose a benzyl radical and/or a benzaldehyde molecule, depending on the length of the aliphatic chain. Both reactions appear to be the result of the transfer of a hydrogen atom to the charge localized amino function in a cyclic transition state. The ring size of this transition state turns out to play a far more important role than the difference in reactivity of the migrating hydrogen atoms.     

Vibronic Dynamics of Photodissociating ICN from Simulations of Ultrafast X-Ray Absorption Spectroscopy

Ultrafast UV-pump/soft-X-ray-probe spectroscopy is a subject of great interest since it can provide detailed information about dynamical photochemical processes with ultrafast resolution and atomic specificity. Here, we focus on the photodissociation of ICN in the ¹Π₁ excited state, with emphasis on the transient response in the soft-X-ray spectral region as described by the ab initio spectral lineshape averaged over the nuclear wavepacket probability density. We find that the carbon K-edge spectral region reveals a rich transient response that provides direct insights into the dynamics of frontier orbitals during the I−CN bond cleavage process. The simulated UV-pump/soft-X-ray-probe spectra exhibit detailed dynamical information, including a time-domain signature for coherent vibration associated with the photogenerated CN fragment.     

Study of the rate of methyl loss and the structure of the product ion as a function of the lifetime of the molecular ion of pent-3-en-2-ol

The normalized unimolecular rate constant for loss of a methyl radical from pent-3-en-2-ol molecular ions with lifetimes ranging from 10^?11 to 10^?9 s was studied by field ionization kinetics (FIK). The normalized rate curve shows maxima at molecular ion lifetimes of 10^?10.5 and 10^?10.1 s. Based on results for deuterium and ¹³C-labelled pent-3-en-2-ol, the maximum at 10^?10.5 s is ascribed to loss of the methyl group at the 1-position by a direct cleavage reaction. The maximum at 10^?10.1 s is attributed to a 1,2-H shift-initiated rearrangement of the molecular ion, which leads to loss of the methyl group at the 5- and 1-positions. The time dependence of the processes in the form of the maxima on the normalized rate curve is discussed qualitatively in terms of a lower critical energy and a tighter transition state of the 1,2-H shift than those of the direct cleavage reaction. Collision-induced dissociation of the [C₄H₇O]⁺ product ions in combination with FIK provides evidence that at molecular ion lifetimes corresponding to the first maximum on the rate curve protonated crotonaldehyde is formed, whereas protonated methyl vinyl ketone and the butyryl cation are formed at times corresponding to the second maximum.     

The role of mass spectrometry in organic chemistry

It is well known that mass spectrometry (MS) is a very versatile physical method which is applied to many branches of chemistry. Two main lines of development can be discerned: (i) organic chemical analysis. (ii) gas phase chemistry of organic ions. Both will be surveyed and discussed and will be followed by some speculations on future developments.