Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Ketoses give Seliwanoff's test faster than Aldoses.
Reason (R) : Ketoses undergo β-elimination followed by formation of furfural.
In the light of the above statements, choose the correct answer from the options given below :
Assertion (A) : Ketoses give Seliwanoff's test faster than Aldoses.
Reason (R) : Ketoses undergo β-elimination followed by formation of furfural.
In the light of the above statements, choose the correct answer from the options given below :
- (A)(A) is false but (R) is true
- (B)Both (A) and (R) are true and (R) is the correct explanation of (A)
- (C)(A) is true but (R) is false✓ Correct
- (D)Both (A) and (R) are true but (R) is not the correct explanation of (A)
Answer: (C)
Solution
In Seliwanoff's test the sugar is warmed with resorcinol in concentrated hydrochloric acid. Ketoses are dehydrated much faster than aldoses, so a ketose gives a cherry-red colour quickly while an aldose reacts only slowly; the assertion is therefore sound. The coloured species is 5-hydroxymethylfurfural, formed by acid-catalysed dehydration of the ketohexose, not furfural, and the route is dehydration rather than a -elimination. Hence the assertion is true while the reason is false.
JEE Main · 2023 · 30 Jan 2023 · Shift 1 · Single correct option