Predict the products obtained when D-galactose reacts with each reagent.
(k) excess HIO₄

Verified step by step guidance

1. Understand the reaction: Periodic acid (HIO4) is an oxidizing agent that cleaves vicinal diols (two hydroxyl groups on adjacent carbons) in carbohydrates. It breaks the C-C bond between the carbons bearing the hydroxyl groups, forming smaller carbonyl-containing fragments such as aldehydes or formic acid.
2. Analyze the structure of D-galactose: D-galactose is an aldohexose, meaning it has six carbons, with an aldehyde group at C1 and hydroxyl groups on the other carbons. Draw the Fischer projection of D-galactose to visualize the vicinal diols.
3. Identify the vicinal diols: In D-galactose, vicinal diols are present between C2-C3, C3-C4, C4-C5, and C5-C6. These are the sites where HIO4 will cleave the C-C bonds.
4. Determine the cleavage products: For each vicinal diol, the C-C bond is broken, and each carbon forms a carbonyl group. Depending on the position of the carbon, the products will be either formaldehyde (HCHO), formic acid (HCOOH), or a larger aldehyde/ketone.
5. Combine the results: After cleaving all vicinal diols in excess HIO4, the D-galactose molecule will be completely broken down into smaller fragments. Write out the specific products formed from each cleavage site to complete the reaction analysis.

Key Concepts

D-Galactose Structure

D-galactose is a six-carbon aldose sugar with a specific stereochemistry. It contains an aldehyde group at one end and multiple hydroxyl groups, which influence its reactivity. Understanding its structure is crucial for predicting how it will react with various reagents, including oxidative agents like HIO4.

Periodic Acid Oxidation

Periodic acid (HIO4) is a strong oxidizing agent that cleaves vicinal diols and aldehydes. In the case of sugars, it can oxidatively cleave the carbon-carbon bonds adjacent to hydroxyl groups, leading to the formation of smaller aldehydes or ketones. This reaction is essential for understanding the products formed when d-galactose is treated with excess HIO4.

Reaction Mechanism

The reaction mechanism describes the step-by-step process by which reactants are converted into products. For d-galactose reacting with HIO4, the mechanism involves the formation of cyclic intermediates and subsequent cleavage of the sugar backbone. A clear grasp of these mechanisms helps in predicting the final products of the reaction.