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.
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
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.