Structural and energetic properties of alkylfluoride–BF3 complexes in the gas phase and condensed‐phase media: computations and matrix infrared spectroscopy |
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Authors: | Robin R Knauf Heather M Helminiak John P Wrass Timothy M Gallert James A Phillips |
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Institution: | Department of Chemistry, University of Wisconsin‐Eau Claire, 105, , Eau Claire, WI 54702 USA |
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Abstract: | We have undertaken an experimental and computational study of the structural properties of a few alkylfluoride–BF3 complexes (RF′–BF3), which are proposed intermediates in a certain class of Friedel–Crafts reactions. Using density functional theory and second‐order Møller–Plesset calculations, we have obtained gas‐phase structures, frequencies, and B–F′ bond potentials for CH3F–BF3, (CH3)2CHF–BF3, and (CH3)3CF–BF3. All the complexes are weakly‐bonded in the gas phase, with B–F′ distances (X3LYP/aug‐cc‐pVTZ) of about 2.4 Å and binding energies (MP2/aug‐cc‐pVTZ) ranging from 5.4 and 6.7 kcal/mol. Accordingly, gas‐phase bond potentials are relatively shallow and flat for these complexes. However, even though the inner walls of the potentials are rather soft (the energies rise by only about 5 to 10 kcal/mol between 2.4 and 1.6 Å), we observe no global or local minima at short B–F′ distances. For the (CH3)2CHF–BF3 and (CH3)3CF–BF3 potentials in dielectric media, we do observe a distinct flattening along the inner wall, which results in shelf‐like region near 1.7 Å, but this feature is not a true local minimum. We have also obtained low‐temperature infrared spectra of the (CH3)2CHF–BF3 complex in solid neon, and the frequencies agree quite favorably with those obtained via computations, which validates the computational assessment of the gas‐phase complexes. Copyright © 2011 John Wiley & Sons, Ltd. |
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Keywords: | BF3 complexes Friedel– Crafts intermediates |
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