This is an example of an electrophilic aromatic substitution reaction. In short, we are substituting a nitro group for a hydrogen on the aromatic ring. Here, the aromatic ring acts as the nucleophile, and the nitronium ion acts as the electrophile. As always, one can view this as a reaction between a Lewis base and a Lewis acid.

Reading Assignment

In addition to SYNT 716, read Section 14.4e, p. 686, in your textbook. This section describes the nitration reaction you will be performing.

In The Beginning

1. Hand-in your Pre-Lab Exercise to the instructor or T.A.
2. Note: nitric acid is a strong acid. It will burn the skin and leave ugly yellow stains.
3. You will use acetanilide as your starting material, not methyl benzoate. Understand: the amide group attached to the benzene ring is an ortho/para director.
4. Make sure you read the instructions at the top of p. 7 of SYNT 716.

Product Characterization

Generally, one knows the structure of the starting material; moreover, one usually has NMR and IR spectra of this substance. As a synthesis is carried out, it is monitoed carefully by considering what functional groups have been added and which have been removed or altered. This is easily done with ¹H and ¹³C NMR, IR spectroscopy; mass spectrometry is also helpful. In the present synthesis a nitro group is being added to the starting material. The relevant IR bands for the nitro group should be present in the IR spectrum of the product, and since we kepp the amide group, the IR bands that were originally present in the starting material should still be present.

The "before" and "after" ¹H and ¹³C NMR spectra are perhaps more interesting and revealing. Consider: in the starting material we have a monosubstituted aromatic ring; in the product we have a para-disubstituted aromatic ring. The difference in the NMR spectra for the starting material and product is quite obvious, and it is clear that the product is a para-disubstituted material. This information along with the presence of bands from nirto in the IR strongly infer that our product is the desired p-nitroacetanilide. The molecular weights, as determined through mass spectrometry, should also be consistent with the structures of the starting materials and product. Follow the logic here.