The drug tegamet is :

Solution

Chemistry ma’am · 3 steps

Tagamet is cimetidine: look for the imidazole ring of histamine joined to a cyano-guanidine chain.

1. What tagamet does. Tagamet (cimetidine) is an antacid. Histamine makes the stomach release acid by binding to its receptors in the stomach wall. Cimetidine blocks histamine from reaching those receptors, so less acid is made.
2. Built like histamine. To block histamine at its receptor, cimetidine was designed to look like histamine. So it keeps histamine's imidazole ring (a five-membered ring with two N atoms). A side chain with S, ending in a cyano-guanidine group (NC-N=C(NHCH₃)NH⁻), is attached to that ring.

   Option	Key features	Compound
   (a)	Imidazole ring with a short CH₂CH₂NH₂ chain	Histamine, the molecule that causes acid release
   (b)	Furan ring, N(CH₃)₂ group, nitro-ethene unit	Ranitidine (zantac), another antacid
   (c)	Methyl-imidazole ring, S in the chain, N-C≡N group	Cimetidine (tagamet)
   (d)	Two OH groups, piperidine ring, three benzene rings	Terfenadine (seldane), an antihistamine for allergy

3. So. Only structure (c) has the imidazole ring joined to the cyano-guanidine chain, so tagamet is option (c).

The idea to keep. Learn the antacid pair together: cimetidine (tagamet) keeps histamine's imidazole ring, while ranitidine (zantac) has a furan ring in its place. The ring tells you which drug it is.

Answer from the NTA final answer key. Solution by PrepWiser.