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Structure, Vibrational Spectra, and Unimolecular Dissociation of Gaseous 1-Fluoro-1-phenethyl Cations

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Abstract

The multiple CF bond character of PhCFMe+ ions has been examined by means of theory, vibrational spectroscopy of the gaseous ions, and unimolecular decomposition chemistry. Atoms in Molecules analysis of DFF wave functions gives a CF bond order of n = 1.25 (as compared with n = 1.38 for Me2CF+, relative to n = 1 for fluoromethane and n = 2 for diatomic CF+), which is consistent with calculations of adiabatic CF stretching frequencies (v(CF)). Experimental gas phase IR spectra, recorded by means of resonant multiphoton dissociation (IRMPD) using a free-electron laser connected to an FFICR mass spectrometer, show good agreement with predicted band positions for five deuterated isotopomers of PhCFMe+. Metastable ion decompositions of deuterated analogues of PhCFMe+ show the same HF/DF loss patterns as those produced by IRMPD. The evidence supports the conclusion that PhCFMe ions retain structural integrity until they become sufficiently excited to dissociate, whereupon they undergo intramolecular hydrogen scrambling that is competitive with HF/DF expulsion. Relative rates of hydrogen transposition and unimolecular dissociation are extracted from relative experimental fragment ion abundances. The predominant decomposition pathway is inferred to operate via a five-center transition state, as opposed to a four-center transition state for HF loss from gaseous Me2CF+.

Year of Publication
2008
Journal
Journal of Physical Chemistry A
Volume
112
Number
43
Number of Pages
10774-10783
Date Published
Oct
Type of Article
Article
ISBN Number
1089-5639
Accession Number
ISI:000260357600012
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PId
2d86e4a7ea8f43b98dbf454c07dc665e
Alternate Journal
J. Phys. Chem. A
Journal Article
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