Question

Consider the two compounds given below. Which of the following best describes the relationship between them?

• A. Resonance structures
• B. Positional isomers
• C. Functional isomers
• D. Tautomers

Hint:

Tautomers differ by proton shift + double bond shift (dynamic equilibrium), not just structure like isomers.

Answer 1

The Correct Option is D

Concept: Tautomerism is a type of isomerism where compounds exist in equilibrium due to the migration of a proton along with a shift of a double bond. A common example is keto–enol or related nitrogen analogues.

Step 1: Observe structural difference.

• First structure: Contains $C=N-OH$ group (oxime form)
• Second structure: Contains $C-H$ and $N=O$ arrangement (nitroso form)

Step 2: Identify transformation.
The two structures differ by:
• Shift of hydrogen atom
• Rearrangement of double bond

Step 3: Classify the relationship.
Such interconversion is characteristic of: \[ \text{Tautomerism} \]

Step 4: Final conclusion.
Thus, the compounds are: \[ Tautomers \]