Substituent effects on the physical properties and pKa of phenol

Abstract Substituent effects on the physical properties and p K a of phenol were studied using density functional theory [B3LYP/6‐311G(d,p)] calculations. Substituents alter the physical properties of phenol such as the hydroxyl‐group CO and OH bond lengths, the C OH bond angle, and the energy barrier to rotation about the C O bond, and also influence the hydroxyl‐group p K a . Except for the rotational barrier, Hammett σ constants showed strong correlation with these property changes. Several quantum chemical parameters, including the natural charge on the phenolic hydrogen Q n (H) and the natural charge on the phenoxide oxygen Q n (O − ), the HF/6‐311G(d,p) HOMO energy E homo , and the proton‐transfer energy Δ E prot , outperformed the empirical Hammett constants in modeling changes in the p K a . All of these latter parameters yielded correlation coefficients ∣ r ∣>0.94 for the p K a . © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001