1. Condensed Phase Effects on the Structural Properties of Friedel-Crafts Intermediates: R-F’–BF3
James A. Phillips, Department of Chemistry, University of Wisconsin – Eau Claire
Organofluoride – boron trifluoride complexes (RF’–BF3) are key intermediates in Friedel-Crafts reactions, an important class of carbon-carbon forming processes that facilitate the conversion of petroleum feedstocks to commercially-viable compounds. The methylation of benzene is a common example:
The first step in this process is the formation CH3F–BF3, which subsequently reacts with the aromatic ring as if it was a carbo-cation. However, this complex is weak in the gas-phase (vide infra), but must undegro major structural changes in solution in order to accomplish the reaction above. We have identified several DFT methods that reproduce the experimental gas-phase structural properties of CH3F–BF3 and HF–BF3, and are in the process of assessing the effects of bulk condensed-phase environments both experimentally, using low-temperature IR spectroscopy and theoretically, via continuum solvation models. A preliminary assessment via PCM calculations indicates that the B-F’ bond shortens by about 0.03Å in chloroform solution.
GAS PHASE
SOLUTION PHASE
CHCl3
From X3LYP/aug-cc-pVTZ calculations. The preliminary experimental gas-phase B–F’ distance is 2.42 Å
From PCM/X3LYP/aug-cc-pVT calculations.