The Deprotonation of Benzyl Alcohol Radical Cations: A Mechanistic Dichotomy in the Gas Phase as in Solution
✍ Scribed by Enrico Baciocchi; Massimo Bietti; Barbara Chiavarino; Maria Elisa Crestoni; Simonetta Fornarini
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 111 KB
- Volume
- 8
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
The gas-phase acidity of ionized benzyl alcohol and of some of its derivatives with selected reference bases has been studied by Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry. The aim was to relate the gas-phase reactivity to the behavior in aqueous solution of the radical cations of benzyl alcohols bearing methoxy substituent(s) on the phenyl ring which are known to undergo deprotonation at both the CH 2 and OH groups. The dual reactivity behavior is confirmed in the gas phase, in which the prototypical ion, C 6 H 5 CH 2 OH . , is deprotonated at both the CH 2 and OH groups, whereas the ring hydrogens are not involved. An increasing extent of O-deprotonation is shown as the strength of the base increases. Appropriate methyl substitution, as in the radical cations of C 6 H 5 C(Me) 2 OH and C 6 H 5 CH 2 OMe, allows only O-or C-acidity. The two processes are characterized by comparable thermodynamic features with a Gas-phase Basicity (GB) value of 852 kJ mol À1 for the cumyloxyl radical and 850 kJ mol À1 for the a-methoxybenzyl radical. The possible origin of the observed mechanistic dichotomy is discussed.
Keywords: cations ¥ gas-phase reactions ¥ mass spectrometry ¥ proton transfer ¥ radicals [a] Prof.