Samet, M.; Buhle, J.; Zhou, Y.; Kass, S. R. J. Am. Chem. Soc., 2015, 137, 4678–4680.
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.