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Chapter 24: Phenols |
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Spectroscopic analyzis:
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IR - presence of -OH and aromatic CC and CH
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Absorbance (cm-1)
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Interpretation
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3600 (strong, broad)
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OH stretch
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> 3000
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aromatic CH stretch
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1600
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CC stretch (pairs)
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1200-1250
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C-O stretch
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1H NMR -OH proton is
more deshielded (higher ppm) in a phenol than in an alcohol.
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Resonance (ppm)
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Interpretation
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4-12 (exchangeable)
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-OH proton
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7-8
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aromatic protons, Ar-H
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(exchangeable means that the peak "disappears" when shaken with D2O)
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13C NMR
C-O carbon in the aromatic ring is deshielded by 25 ppm vs the
aromatic C-H carbons
Most shielded C-H carbons of ring are located ortho and para
to the OH (recall resonance forms)
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UV-VIS
-OH group affects benzene chromophore by shifting
lmax to longer wavelengths.
The effect is very large in basic solution as a result of OH conversion
to O-.
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Mass Spectrometry
Peak for the molecular ion, M+, is usually prominent
