Question

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 -elimination followed by formation of furfural
In the light of the above statements, choose the correct answer from the options given below:

• A. Both (A) and (R) are true but $( R )$ is not the correct explanation of (A)
• B. (A) is false but (R) is true
• C. (A) is true but (R) is false
• D. Both (A) and (R) are true and (R) is the correct explanation of (A)

Hint:

When studying organic tests, remember the key principle behind each test. For example, Seliwanoff’s test differentiates between Ketoses and Aldoses based on the rate of dehydration to form furfural.

Answer 1

The Correct Option is C

To evaluate the given statements, we need to understand Seliwanoff's test and the behavior of ketoses and aldoses in it.

Assertion (A): Ketoses give Seliwanoff's test faster than Aldoses.
Reason (R): Ketoses undergo -elimination followed by formation of furfural.

Seliwanoff's test is a chemical test to distinguish ketohexoses (such as fructose) from aldohexoses (such as glucose). In this test, when heated with resorcinol and conc. hydrochloric acid, ketoses react faster to produce a deep red color compared to aldoses, due to the faster dehydration reaction of ketoses to form reactive intermediates, which then condense with resorcinol to give the colored complex.

The key points to assess:

• The assertion is indeed correct because ketoses generally react faster in Seliwanoff's test.
• However, the reason provided is not accurate. While furfural derivatives are formed, the mechanism described as '-elimination followed by formation of furfural' does not accurately capture the process at play in Seliwanoff's test as it involves the formation of hydroxymethylfurfural, not simply furfural.
  This process primarily involves dehydration, rather than a simple -elimination.
  Thus, (R) does not correctly explain (A).

Based on this analysis, the correct choice is:

(A) is true but (R) is false

Answer 2

To determine the correctness of the statements given, we need to analyze both the Assertion (A) and the Reason (R) concerning their factual accuracy and logical connection:

Assertion (A): Ketoses give Seliwanoff's test faster than Aldoses.

Reason (R): Ketoses undergo -elimination followed by formation of furfural.

Seliwanoff's test is a chemical test that distinguishes between ketoses and aldoses. In this test, ketoses react more quickly and produce a deeper cherry-red color compared to aldoses when heated with resorcinol and hydrochloric acid. This occurs because ketoses are more easily dehydrated than aldoses, leading to rapid formation of furfural derivatives. Therefore, Assertion (A) is true.

Now, analyzing the Reason (R): The statement mentions "-elimination followed by formation of furfural." The process involved in Seliwanoff's test for ketoses primarily involves dehydration to form furfural derivatives directly, without explicit mention of "-elimination" as a standalone process. Hence, Reason (R) is not an accurate explanation of why ketoses react faster in Seliwanoff's test; instead, it is due to their easier dehydration into furfural-like compounds.

Thus, the correct conclusion is:

(A) is true but (R) is false