The unimolecular chemistry of quaternary ammonium ions and their neutral counterparts

Sarka Beranova, Chrys Wesdemiotis

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

The quaternary ammonium ions (CH3)4N+ (1+), (CH3CH2)4N+ (2+), C6H5N+ (CH3)3(3+), C6H5CH2N+ (CH3)3 (4+) and C6H5CH2N+ (CH2CH3)3 (5+) and the corresponding ammonium radicals 1-5 have been studied in the gas phase by metastable ion (MI) characteristics, collisionally activated dissociation (CAD) and neutralization-reionization mass spectrometry (NRMS). The unimolecular chemistry of the ammonium ions is influenced by the nature of their substituents (R). Based on cations 3+-5+, which carry different types of N+R bonds, preferential dissociation at N+-benzyl > N+-alkyl > N+-phenyl takes place. The two major fragmentation channels observed for all ions are (i) direct cleavage of the N+R bond with charge retention on the species of lowest ionization energy and (ii) formation of an immonium ion by loss of the hydrocarbon RH (from all cations) or RCH3 (only from 2+ and 5+). These decompositions proceed after initial, rate-determining isomerization of 1+-5+ to ion/dipole complexes R3N{radical dot}+/{radical dot}R or, in case of benzyl substitution, to R+/NR3. The NRMS experiments reveal that the hypervalent radicals 1-5 are unstable, decaying within ≪ 0.2 μs by rupture of one of the NR bonds. 3-5 mainly cleave the NR bond which yields the thermodynamically most stable products.

Original languageEnglish (US)
Pages (from-to)83-102
Number of pages20
JournalInternational Journal of Mass Spectrometry and Ion Processes
Volume134
Issue number2-3
DOIs
StatePublished - Jun 30 1994
Externally publishedYes

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Ammonium Compounds
Ions
chemistry
ions
Mass spectrometry
Cations
mass spectroscopy
Positive ions
dissociation
cations
Ionization potential
Isomerization
Hydrocarbons
isomerization
cleavage
fragmentation
Substitution reactions
hydrocarbons
Gases
substitutes

All Science Journal Classification (ASJC) codes

  • Spectroscopy

Cite this

The unimolecular chemistry of quaternary ammonium ions and their neutral counterparts. / Beranova, Sarka; Wesdemiotis, Chrys.

In: International Journal of Mass Spectrometry and Ion Processes, Vol. 134, No. 2-3, 30.06.1994, p. 83-102.

Research output: Contribution to journalArticle

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