Phenols

Phenol The antiseptic property of phenol was discovered in 1865 by Joseph Lister, a physician in Scotland. Listerine, named after him, contains phenol as the active ingredient. Today, over two million tons of phenol are made each year in the US alone. Phenol is used for resins, glue to make plywood, plastics, and pharmaceuticals.

Examples of Phenols

More phenols…

Slight Acidity of Phenol Phenol has a K a = (pK a =10) Alcohols have a K a = (pK a =16) The reason phenol is more acidic than an alcohol is resonance stabilization of the phenolate anion (next slide)

Resonance of Phenolate ion Substituents that stabilize an anion enhance the acidity of phenol. Phenol has a pK a = 10; p-nitrophenol has a pK a = 7.1

Picric acid (2,4,6-trinitrophenol) 2,4,6-trinitrophenol is so acidic that it is called picric acid; it has a K a = (pK a =1) The enhanced acidity compared to phenol itself (K a = ) is due to the increased resonance stabilization of the conjugate base (phenolate anion) by the nitro groups:

IR spectrum of phenol O-H C=C C-O

IR spectrum of cyclohexanol O-H C-O

O-H C-O O-H C-O IR spectrum of 1-butanol

H H H

Summary of Spectral Features IR:O-H stretch, cm -1, broad (alcohols and phenols) C-O stretch, 1250 to 1050 cm -1, (higher for phenols than for alcohols) 13 C-NMR:C-O,  alcohols    phenols  1 H-NMR:-CH 2 -O, 3.5 