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Gaseous [C_nH_2n+1+ ... 1,3-Diphenylpropane] Ion/Neutral Complexes Containing Alkyl Cations of Different Acidities and Hydride Ion Affinities

Carsten Matthias ; Department of Chemistry, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
Dietmar Kuck ; Department of Chemistry, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany

Sažetak

Gaseous ion/neutral (I/N) complexes [R+ ... C₆H₅CH₂CH₂CH₂C₆H₅] with R = t-C₄H₉+, s-C₄H₉+ and s-C₃H₇+ have been generated by protonation of the corresponding precursor compounds,
R-C₆H₄CH₂CH₂CH₂C₆H₅, in the chemical ionisation (CI) source of a sector-field mass spectrometer. The fragmentation of these I/N complexes and several deuterium-labelled isotopologues on the metastable ions’ timescale (20−30 μs), as studied by MIKE spectrometry, revealed that (i) the initial ring position
(meta- or para-) of R = t-C₄H₉+ does not affect their intra-complex reactivity, (ii) the fragmentation of the s-C₃H₇+ and s-C₄H₉+ ions is dominated by proton transfer to the 1,3-diphenylpropane neutral but hydride ion abstraction in the reverse direction competes to a minor extent, (iii) the secondary alkyl cations exhibit the same regioselectivity (k_α-H/k_ω-H = 1.0) and kinetic isotope effect (k_H/k_D = 1.6) in the hydride transfer channel as do tertiary alkyl cations, (iv) the s-C₄H₉+ ions do not undergo skeletal isomerisation to t-C₄H₉+ ions within the I/N complex. Attempts to characterise the trimethylsilyl complex, [Si(CH3)3
+ ∙∙∙
C₆H₅CH₂CH₂CH₂C₆H₅], by CI/MIKE spectrometry under analogous conditions failed.

Ključne riječi

proton transfer; hydride ion transfer; alkyl cations; ion/neutral complexes (gaseous); mass spectrometry; metastable ions

Hrčak ID:

37871

URI

https://hrcak.srce.hr/37871

Datum izdavanja:

30.6.2009.

Posjeta: 1.589 *