Question

In the determination of configuration of glucose, Fischer subjected (‐) arabinose to Ruff’s degradation. The four‐carbon sugar obtained by the degradation process was:

• A. (‐) Threose
• B. (+) Threose
• C. (‐) Erythrose
• D. (+) Erythrose

Answer 1

The Correct Option is C

To determine the four-carbon sugar obtained by Ruff's degradation of (‐) arabinose, we need to understand the process and the configuration changes involved: 

1. Ruff's degradation is a method used in carbohydrate chemistry to shorten the chain length of aldoses by one carbon atom. It consists of two main steps:
   • Oxidation of the aldehyde group to a carboxylic acid using bromine water in the presence of barium carbonate.
   • Decarboxylation using hydrogen peroxide and ferric sulfate to remove the carboxyl group, resulting in a sugar with one less carbon atom.
2. (‐) Arabinose is a five-carbon sugar (aldopentose) with the configuration (2S,3S,4R).
3. Upon applying Ruff's degradation to (‐) arabinose, the oxidation and decarboxylation steps lead to the removal of the carbon at the aldehyde end.
4. The resulting sugar retains the stereochemistry of the remaining chiral centers. Therefore, the configuration of the three centers left (2S,3S) leads to the formation of (‐) Erythrose.

Thus, the four-carbon sugar produced is (‐) Erythrose. Justifying the other options:

(‐) Threose: Incorrect because the stereochemistry doesn't match the configuration resulting from Ruff's degradation of (‐) arabinose.

(+) Threose: Incorrect for the same reason as above, plus the sign indicates a different optical activity.

(+) Erythrose: Incorrect as it suggests opposite optical activity to (‐) Erythrose.

Hence, the correct answer is (‐) Erythrose.