Protonation sites of isolated fluorobenzene revealed by IR spectroscopy in the fingerprint range.
Protonated fluorobenzene ions (C6H6F+) are produced by chemical ionization of C6H5F in the cell of a FT-ICR mass spectrometer using either CH5+ or C2H5+. The resulting protonation sites are probed by IR multiphoton dissociation (IRMPD) spectroscopy in the 600-1700 cm-1 fingerprint range employing the free electron laser at CLIO (Centre Laser Infrarouge Orsay). Comparison with quantum chemical calculations reveals that the IRMPD spectra are consistent with protonation in para and/or ortho position, which are the thermodynamically favored protonation sites. The lack of observation of protonation at the F substituent, when CH5+ is used as protonating agent, is attributed to the low-pressure conditions in the ICR cell where the ions are produced. Comparison of the C6H6F+ spectrum with IR spectra of C6H5F and C6H7+ reveals the effects of both protonation and H F substitution on the structural properties of these fundamental aromatic molecules.
Dopfer
Otto
O
Institut für Physikalische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. dopfer@phys-chemie.uni-wuerzburg.de
Solcà
Nicola
N
Lemaire
Joel
J
Maitre
Philippe
P
Crestoni
Maria-Elisa
ME
Fornarini
Simonetta
S
D005464:Fluorobenzenes / Q000737:chemistry*; D011522:Protons; D013055:Spectrophotometry, Infrared / Q000379:methods*
D005464:Fluorobenzenes; D011522:Protons