Charge-enhanced acidity and catalyst activation.

Acidities are commonly measured in polar solvents but catalytic reactions are typically carried out in nonpolar media. IR spectra of a series of phenols in CCl4 and 1% CD3CN/CCl4 provide relative acidities. Nonprotonated charged substituents with an appropriate counterion are found to enhance their Brønsted acidities and improve catalyst performance by orders of magnitude.