NEETChemistryAldehydes and Ketones
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Reaction of pentane-2,4-dione with excess NaBH ₄ followed by heating with conc. H ₂ SO ₄ yields penta-1,3-diene as the major product. Reason (R): NaBH ₄ reduces both the carbonyl groups to alcohols, which then undergo dehydration to form a thermodynamically stable conjugated diene. In the light of
Options
- ABoth Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- BBoth Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
- CAssertion (A) is true but Reason (R) is false.
- DAssertion (A) is false but Reason (R) is true.
Correct answer
A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Step-by-step solution
NaBH ₄ is a reducing agent that reduces aldehydes and ketones to alcohols. It reduces both the ketone groups of pentane-2,4-dione to form pentane-2,4-diol. When pentane-2,4-diol is heated with concentrated H ₂ SO ₄ , it undergoes acid-catalysed dehydration. Elimination of two water molecules occurs to form a diene. To achieve maximum thermodynamic stability, the double bonds are formed in conjugation. Thus, the major product is the conjugated diene, penta-1,3-diene, rather than the isolated penta-1,4-diene. Therefo