Question
The hydrogen in the hydroxyl group of phenols is particularly acidic because ____.
Answer
The hydrogen in the hydroxyl group of phenols is particularly acidic because the oxygen-containing anion is resonance-stabilized by the ring.
Note ↓: Phenol is a very weak acid and the position of equilibrium lies well to the left. Phenol can lose a hydrogen ion because the phenoxide ion formed is stabilised to some extent. The negative charge on the oxygen atom, resulting from loss of hydrogen, is delocalised around the ring. The more stable the ion is, the more likely it is to form.
Figure ↓: Phenols have pKa values that range from 8 to 10. Even though they are less acidic than
carboxylic acids (pKa = 3–5), they are stronger than alkanols (pKa = 16–18). The reason
is resonance: The negative charge in the conjugate base, called the phenoxide ion, is stabilized
by delocalization into the ring. Phenols are acidic because the corresponding anions are resonance
stabilized.
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Alcohols have the general formula ____.
The functional group ____ is referred to as a hydroxyl group.
The functional group –OH is referred to as a ____ group.
Hydroxyl groups attached to aromatic rings are called ____.
Hydroxyl groups attached to ar____e called phenols.
____ attached to aromatic rings are called phenols.