stabilization of the negative charge on oxygen, stabilizing the anion. Like other alcohols, phenols
form intermolecular hydrogen bonds and have relatively high melting and boiling points. Phenol is
slightly soluble in water, owing to hydrogen bonding, as are some of its derivatives. Because phenols
are much more acidic than nonaromatic alcohols, they can form salts with inorganic bases such as
NaOH.
The presence of other substituents on the ring has significant effects on the acidity, boiling points,
and melting points of phenols. As with other compounds, electron-withdrawing substituents
increase acidity, and electron-donating groups decrease acidity.
KEY CONCEPT
Charges like to be spread out as much as possible. Acidity decreases as more alkyl groups are
attached because they are electron-donating, which destabilizes the alkoxide anion.
Resonance or electron-withdrawing groups stabilize the alkoxide anion, making the alcohol
more acidic.Another trend seen in Table 5.1 is that the presence of more alkyl groups in nonaromatic alcohols
produces less acidic molecules. Because alkyl groups donate electron density, they destabilize a
negative charge. Additionally, alkyl groups help stabilize positive charges, explaining why more
substituted carbocations have higher stability than less substituted carbocations.
MCAT Concept Check 5.1:
Before you move on, assess your understanding of the material with these questions.Which has a lower pKa: ethanol or p-ethylphenol? Why?