Bis- and Oligo(trifluoromethyl)benzenes: Hydrogen/Metal Exchange Rates and Gas-Phase Acidities

To what extent do trifluoromethyl groups stabilize electron excess? An unequivocal answer was deduced from gas-phase equilibration between two acid/base couples, one of them composed of an arene carrying zero, one, two, three trifluoromethyl substituents and the corresponding aryl anion. Depending on its distance from the anionic site, a CF3 unit stabilizes the latter by up to 13 kcal mol−1, and the effects of two or more substituents are additive. On the other hand, when strong bases are employed in solution to generate organometallic species under irreversible conditions, the relative rates of deprotonation are unpredictable since steric hindrance exerted by the CF3 groups and side reations now play a crucial role.