Q.What happens when D-glucose is treated with the following reagents? (1+1=2)

The key idea is that D-glucose, a polyhydroxy aldehyde, undergoes characteristic reactions based on the strength of the reagent, either reducing it completely or oxidizing specific functional groups.

(a) When D-glucose is treated with HI:

1. HI is a strong reducing agent, especially when heated.
2. It reduces all the hydroxyl groups and the aldehyde group of D-glucose. …

D-glucose is an aldohexose, meaning it is a six-carbon sugar with an aldehyde group ($-\text{CHO}$) at one end and multiple hydroxyl groups ($-\text{OH}$). While glucose primarily exists in cyclic hemiacetal forms in solution, its reactions with strong reagents like HI and concentrated $HNO_3$ often proceed via its open-chain form, where the functional groups are fully exposed. The nature of the reagent dictates whether the functional groups are reduced or oxidized.

(a) Reaction with HI

1. Understanding the Reagent: Hydrogen iodide (HI), especially when heated, is a very strong reducing agent. It is capable of reducing not only aldehyde groups but also all hydroxyl groups present in an organic molecule.
2. Structure of D-Glucose: In its open-chain form, D-glucose has an aldehyde group at carbon C1 and five hydroxyl groups. One of these is a primary alcohol group at C6, and the other four are secondary alcohol groups at C2-C5.

3. The Reduction Process: When D-glucose is heated with HI, all the oxygen-containing functional groups are completely removed. The aldehyde group ($-\text{CHO}$) is reduced to a methyl group ($-\text{CH}_3$), and all the hydroxyl groups ($-\text{OH}$) are reduced to hydrogen atoms ($-\text{H}$). This process effectively deoxygenates the molecule, leaving behind a straight-chain alkane.
4. Product Formation: Since D-glucose has a six-carbon straight chain, the complete reduction yields n-hexane. This reaction is historically significant as it provided crucial evidence for the straight-chain structure of glucose.

(b) Reaction with Conc. $HNO_3$

1. Understanding the Reagent: Concentrated nitric acid ($HNO_3$) is a strong oxidizing agent. It is capable of oxidizing both aldehyde groups and primary alcohol groups to carboxylic acid groups ($-\text{COOH}$). Secondary alcohol groups are generally resistant to oxidation by concentrated $HNO_3$ under these conditions.
2. Structure of D-Glucose: As discussed, D-glucose has an aldehyde group at C1 and a primary alcohol group at C6. …