Compounds containing a hydroxyl group attached to a benzene ring are called phenols. Derivatives of phenols,
such as naphthols and phenanthrols, have chemical properties similar to those of phenols, as do most of the
many naturally-occurring substituted phenols. Like other alcohols, phenols have higher boiling points than
hydrocarbons of similar molecular weight. Like carboxylic acids, phenols are more acidic than their alcohol
counterparts. Phenols undergo a number of different reactions; both their hydroxyl groups and their benzene
rings are highly reactive. A number of chemical tests can be used to distinguish phenols from alcohols and
carboxylic acids.
Thymol, a naturally occurring phenol, is an effective disinfectant that is obtained from thyme oil. Thymol can
also be synthesized from m-cresol, as shown in Reaction A below. Thymol can then be converted to menthol,
another naturally-occurring organic compound; this conversion is shown in Reaction B.
Reaction A
Reaction B
Comparing the Ka values for cyclohexanol (Ka = 10−13) and phenol (Ka = 1.3 × 10−10) reveals that phenol is more
acidic than cyclohexanol. Which of the following explain(s) the acidity of phenol?
I. The exceptionally strong hydrogen bonding possible with phenol facilitates the loss of a proton, making it
more acidic than cyclohexanol.
II. Phenol’s conjugate base, phenoxide, is stabilized by resonance to a greater extent than phenol itself.
III. The negative charge of the oxygen atom on the phenoxide ion is delocalized over the benzene ring.
Section: Biological Sciences