Once we have determined that a compound contains a chlorine atom, there are two possible organic compounds: chloroalkanes and acid chlorides.
The main difference is the presence of the C=O bond in the acid chloride (it is not present in a chloroalkane). This is seen in two of our spectra:
Infrared (IR) Spectroscopy
If we compare these two structures, we can see that they contain different bonds. These should appear as characteristic differences in their respect IR Spectra.
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| Chloroethane |
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| Ethanoyl Chloride |
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| Chloroethane |
We can see a C-Cl stretch between 785-510 cm-1. This is evidence that this compound contain chlorine. However, it does not have a stretch or bend between 1810-1774 cm-1, which is necessary for an acid chloride (due to the C=O bond). We do see this feature in the IR spectrum for ethanoyl chloride (below).
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| Ethanoyl Chloride |
The C-Cl stretch is still present, but now you can clearly see the C=O stretch as well. This must be an acid chloride, not a chloroalkane.
13C-NMR
There is a characteristic shift (165-195ppm) with the C=O bond that will be present in the NMR spectra for acid chlorides, and will be absent from chloroalkanes:
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