An organic compound with fishy smell is likely to have a general formula?

Analyze the question: The question asks which class of organic compounds is known for a fishy smell, and which general formula represents it.

Explain the concept: Amines are organic derivatives of ammonia (NH₃), in which one or more hydrogen atoms are replaced by alkyl or aryl groups. Low-molecular-weight amines, such as methylamine and trimethylamine, have a characteristic fishy odour. This is the smell of decaying fish, because the breakdown of proteins releases amines.

Check each option:

• A. RCONHR¹ is a substituted (N-alkyl) amide. Amides are generally odourless solids or have little smell.
• B. RCONH₂ is a primary amide, such as ethanamide. It is a solid with a faint or mousy smell, not a fishy one.
• C. RNH₂ is a primary amine. The general formula of amines, whose lower members smell fishy, matches the question.
• D. RCOR¹ is a ketone. Ketones have a sweet or sharp smell, like propanone (acetone), not a fishy one.

Answer: The fishy smell belongs to amines, and among the options the amine is RNH₂, which is option C.

Exam tip: Link the smell to the functional group:

• Amines → fishy
• Esters → fruity or sweet
• Carboxylic acids → pungent or vinegary (the lower members)
• Ketones → sweet or sharp (like nail-polish remover)

Remember the pairing "Amine = Ammonia-like = Fish" and you will not lose this mark.