Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

28. Carbohydrates

Monosaccharides - Reduction (Alditols)

Organic Chemistry

28. Carbohydrates

Monosaccharides - Reduction (Alditols)

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2:42 minutes

Problem 34c

Textbook Question

What product or products are obtained when D-galactose reacts with each of the following?
c. NaBH₄, followed by H₃O⁺

Verified step by step guidance

Identify the functional groups present in d-galactose. D-galactose is an aldose sugar, meaning it contains an aldehyde group (-CHO) at the anomeric carbon and multiple hydroxyl (-OH) groups.

Understand the role of NaBH4 (sodium borohydride). NaBH4 is a reducing agent that specifically reduces aldehydes and ketones to their corresponding alcohols. In this case, the aldehyde group in d-galactose will be reduced to a primary alcohol (-CH2OH).

Write the reaction mechanism for the reduction. NaBH4 donates a hydride ion (H⁻) to the carbonyl carbon of the aldehyde group, converting it into an alkoxide intermediate. This intermediate is then protonated by H3O+ (acidic workup) to form the primary alcohol.

Determine the structure of the product. After the reduction, the aldehyde group at the anomeric carbon of d-galactose is replaced by a primary alcohol group (-CH2OH), while the rest of the molecule (the hydroxyl groups on the other carbons) remains unchanged.

Conclude the reaction outcome. The product of this reaction is d-galactitol (also known as dulcitol), a sugar alcohol derived from d-galactose. No other products are formed in this reaction.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reduction Reactions

Reduction reactions involve the gain of electrons or hydrogen, or the loss of oxygen. In organic chemistry, this often refers to the conversion of carbonyl groups (like aldehydes and ketones) into alcohols. In the case of d-galactose, the reaction with NaBH4, a strong reducing agent, will reduce the aldehyde group to a primary alcohol.

Hydrolysis

Hydrolysis is a chemical reaction that involves the breaking of a bond in a molecule using water. In the context of the reaction with H3O+, hydrolysis can help in converting any intermediate formed during the reduction into a stable product. This step is crucial for ensuring that the final product is in its desired alcohol form after reduction.

Stereochemistry of Sugars

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. d-Galactose is a stereoisomer of glucose, and its specific configuration influences the outcome of reactions. Understanding the stereochemistry of d-galactose is essential for predicting the structure of the final product after reduction and hydrolysis.

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Related Practice

Textbook Question

What monosaccharide is reduced to two alditols, one of which is the alditol obtained from the reduction of

1. D-talose?

2. D-allose?

Textbook Question

When D-glucose is reduced with sodium borohydride, optically active glucitol results. When optically active D-galactose is reduced, however, the product is optically inactive. Explain this loss of optical activity.

Multiple Choice

Which enzyme catalyzes the breakdown of starch into sugars?

Multiple Choice

Determine the structure of the alditol formed when b-D-xylofuranose is treated with NaBH4 and then water. Explain how NaBH4 can reduce the hemiacetal group of the furanose.

Textbook Question

Predict the products obtained when D-galactose reacts with each reagent.

(h) NaBH₄

Textbook Question

Predict the products obtained when D-galactose reacts with each reagent.

(e) H₂, Ni

Textbook Question

Identify the sugar in each description.

a. An aldopentose that is not D-arabinose forms D-arabinitol when it is reduced with NaBH₄.

Textbook Question

Identify the sugar in each description.

c. A ketose that, when reduced with NaBH₄, forms D-altritol and D-allitol.