Friedrich Borchers

Kinetic differentiation between non-specific hydrogen rearrangement and hydrogen scrambling in phenyl n-propyl ether. A field ionisation and collisional activation study

Abstract The different kinetics of non-specific hydrogen rearrangements on the one hand, and hydrogen scrambling processes on the other, can be used to distinguish between these two processes as demonstrated for C3H6 elimination from the phenyl n-propyl ether molecular ion. The kinetic results support the conclusion, reached previously in an electron-impact study [2], that the rearrangement in phenyl alkyl ethers is a non-specific hydrogen transfer involving transition states of different ring sizes. Collisional activation spectra, reported in this study, show that the [C6H6O]+− ion formed by this rearrangement has the structure of the ionised phenol, which suggests that the hydrogen atoms from all positions of the side chain are transferred to the oxygen and not to the ortho-position of the phenyl ring.

Genese von C7H8+− aus n-pentylbenzol-radikalkationen zwischen 10−10 und 10−5 s: Eine fik-studie zu kompetitiven wasserstoff-umlagerungen [1]

Zusammenfassung Feldionisationskinetik-Messungen (FIK) an mehreren 2H-markierten n-Pentylbenzol-derivaten belegen, dass an der C7H8+−-Genese der Wasserstoff der Seitenkette uber funf-, sechs- und siebengliedrige Ubergangszustande transferiert wird. Bei den kurzest messbaren Zeiten (t

Stossinduzierte acetylen-eliminierung aus 13C-markier-tem hexadien-(1.3)-in-(5). Ein beitrag zur struktur langlebiger C6H6+--ionen☆

Zusammenfassung Durch CA-Untersuchung wird belegt, dass das C 6 H 6 +- -Ion der Titel-verbindung vor der Acetylen-Eliminierung zu einem Benzol-Radikalkation isomerisiert. Dies bedeutet u.a., dass die H-Scrambling-Prozesse von Benzol tatsachlich uber reversibel Gleichgewichtsreaktionen verlaufen, an denen auch acyclische Species beteiligt sein mussen.

Competing hydrogen rearrangements in the molecular ions of aliphatic esters:an ion lifetime study

Abstract The competition of the two most important hydrogen rearrangements in the molecular ion of aliphatic esters (formation of an alkene ion and the protonated acid) has been studied as a function of the ion lifetime for n-butyl acetate and propionate as well as n-propyl, n-butyl and n-pentyl butyrate. It is shown that, at lifetimes up to 10−11 s after ionization, the transitions-state geometry determines the relative ratio of the rates of formation of these two species. At longer lifetimes the decomposition can be explained in terms of the energetics, as shown by approximate calculation of the activation energies from thermodynamic data and by determination of appearance potentials.

Massenspektrometrische Untersuchungen zur Genese von [M—Me] [M-Et] [C7H7]+ und [C7H8]+ aus n-Butyl- und n-Pentylbenzol: Zeitabhängige Nachbargruppeneffekte, Isomerisierungen und kompetitive Wasserstoff-Umlagerungen / Mass Spectrometric Investigations on the Formation of [M-Me] [M-Et] [C7H7]+ und [C7H8]+ from w-Butyl and w-Pentyl Benzenes: Time Dependent Neighbouring Group Participation, Isomerization and Competitive Hydrogen Rearrangements

Abstract The details of the elimination of CH3· and C2H5· from the molecular ions of n-butyl and n-pentyl benzenes as well as the formation of C7H7+ and C7H7+ -have been established using a combination of different mass spectrometric techniques. Among these techniques are field ionization kinetics (FIK), collisional activation (CA), unimolecular decomposi-tion of metastable ions (MI), kinetic energy release determinations (Tkin)> appearance potential measurements (AP) as well as high resolution mass spectrometry. The appli-cation of these methods and the investigation of nine 13 carbon and eleven deuterium labelled n-butyl and n-pentyl benzenes clearly demonstrate that 1) the loss of methyl and ethyl from terminal positions of the alkyl chains are accompanied by an interaction with the phenyl ring and 2) the regioselectivity of these processes is time dependent. Contrary to previous conclusions it is shown that hydrogen transfer in the formation of C7H8+ -occurs via five-, six-and seven-membered transition states. The time dependence of the hydrogen exchange reaction preceding the alkene eliminations is discussed in detail.

Isomeric gaseous C2H4Cl+ ions

Gaseous ethylenechloronium ions and their methylchlorocarbenium isomers are stable and can be identified from their collisition activation spectra.

Stoßaktivierungsmassenspektrometrie von Monoterpenen und Isomerisierung von C7H9+-Ionen in der Gasphase.

The molecular ions of ten monoterpenes show no or only minor isomerisation to a common intermediate or an equal mixture of structures prior to or during collisional activation. The C7H9+ions, however, from these monoterpenes and some other precursors exhibit the same abundance ratios for their collision induced decompositions. From the characteristic release of kinetic energy possible structures of the decomposing gaseous C7H9+ions can be elucidated. It is shown that the ions eliminating H2 resp. CH4 possess a different structure in the transition state.