Phenols

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Phenols
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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.

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Examples of Phenols
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More phenols
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Slight Acidity of Phenol

• Phenol has a Ka 10-10 (pKa 10)
• Alcohols have a Ka 10-16 (pKa 16)
• The reason phenol is more acidic than an alcohol
  is resonance stabilization of the phenolate anion
  (next slide)

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Resonance of Phenolate ion
Substituents that stabilize an anion enhance the
acidity of phenol. Phenol has a pKa 10
p-nitrophenol has a pKa 7.1
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Picric acid (2,4,6-trinitrophenol)

• 2,4,6-trinitrophenol is so acidic that it is
  called picric acid it has a Ka 10-1 (pKa 1)
• The enhanced acidity compared to phenol itself
  (Ka 10-10) is due to the increased resonance
  stabilization of the conjugate base (phenolate
  anion) by the nitro groups

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IR spectrum of phenol
O-H
C-O
CC
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IR spectrum of cyclohexanol
O-H
C-O
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IR spectrum of 1-butanol
C-O
O-H
C-O
O-H
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H
H
H
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Summary of Spectral Features

• IR O-H stretch, 3600-3000 cm-1, broad
• (alcohols and phenols)
• C-O stretch, 1250 to 1050 cm-1, (higher
• for phenols than for alcohols)
• 13C-NMR C-O, 60-65 d (alcohols)
• 160 d (phenols)
• 1H-NMR -CH2-O, 3.5 d