Spectroscopic Features of Alcohols

IR Spectroscopy

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Alcohols are easily recognized by the broad, strong O-H stretching band between 3300-3500 cm^-1.  Note that this is a different band from the (usually present) C-H bands around 3000 cm^-1.

Most other bands are complex vibrations of the molecule. Click on any IR peak to see what vibration is activated by absorption at that frequency.

The O-H peak here is abnormally sharp for an alcohol (the spectrum is actually collected in the gas phase). See several examples below for more "normal" solution behavior.
Cyclohexanol, another aliphatic alcohol. This shows both the broad, H-bonded peak and a sharper peak from the monomeric form.
1-Naphthalenol, an example of a phenol. Note the sharper band.

¹H NMR Spectroscopy

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There are two signals of interest.  The O-H proton is highly variable in its chemical shift, but is normally broad (due to H-bonding) and not coupled to other protons except under special circumstances.  A significant experiment is D₂O exchange; the deuterium will exchange with the OH; the signal will move or disappear altogether.

The second signal is that for any proton on the oxygen-bearing carbon; this will occur between 3.5-4.5 ppm and will couple normally to its neighbors (but not usually to the OH).

¹³C NMR Spectroscopy

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Carbons bearing an oxygen are deshielded and normally occur in the 60-80 ppm region; a carbon with more than one oxygen may be further downfield.

Other carbons in this molecule occur further upfield, as they should. The oxygen exerts a slight influence on those closest. Select each signal to see which carbon generates it.

Mass spectrometry