Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

15. Aldehydes and Ketones

Hemiacetal and Acetal Formation

GOB Chemistry

15. Aldehydes and Ketones

Hemiacetal and Acetal Formation

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Problem 47b

Textbook Question

Acetals and ketals are usually made by reaction of an aldehyde or ketone with two molecules of a monoalcohol. If an aldehyde or ketone reacts with one molecule of a dialcohol, however, a cyclic acetal or ketal results.
b. Draw the cyclic ketal formed when the hemiketal from part (a) reacts with the ―OH labeled in blue.

Verified step by step guidance

Identify the functional groups in the starting material. In this case, the starting material is a hemiketal, which contains both an alcohol (-OH) group and an ether (-OR) group attached to the same carbon atom.

Recognize that the reaction involves a dialcohol (a molecule with two -OH groups) and that one of these -OH groups is labeled in blue. The reaction will form a cyclic ketal by replacing the -OH group of the hemiketal with a bond to the dialcohol.

Understand the mechanism: The -OH group of the hemiketal reacts with the -OH group of the dialcohol in a condensation reaction, releasing a molecule of water (H₂O). This forms a new ether bond between the hemiketal and the dialcohol.

Determine the structure of the cyclic ketal: The dialcohol forms a ring by connecting its two -OH groups to the carbon atom of the hemiketal. The size of the ring depends on the number of carbon atoms in the dialcohol chain.

Draw the final cyclic ketal structure: Ensure that the carbon atom originally part of the hemiketal is now part of the ring, with two ether (-OR) groups attached to it. Verify that the labeled -OH group in blue is part of the new ether bond in the cyclic structure.

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Key Concepts

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

Acetals and Ketals

Acetals and ketals are functional groups formed from the reaction of aldehydes or ketones with alcohols. An acetal is derived from an aldehyde, while a ketal comes from a ketone. The reaction typically involves the nucleophilic attack of the alcohol on the carbonyl carbon, leading to the formation of a hemiacetal or hemiketal intermediate before the final acetal or ketal is formed.

Cyclic Acetals and Ketals

Cyclic acetals and ketals are formed when a dialcohol reacts with an aldehyde or ketone, resulting in a ring structure. This reaction involves the formation of a five- or six-membered ring, which stabilizes the molecule. The cyclic structure is significant in organic chemistry as it can influence the reactivity and properties of the compound, making it more resistant to hydrolysis compared to its acyclic counterparts.

Hemiketal Formation

A hemiketal is an intermediate compound formed when a ketone reacts with one molecule of alcohol. It contains both an alcohol and a carbonyl group, making it a key step in the synthesis of ketals. Understanding hemiketal formation is crucial for predicting the outcome of subsequent reactions, such as the formation of cyclic ketals when a hemiketal reacts with another alcohol.

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Related Practice

Textbook Question

For each compound shown next, determine whether it is a hemiacetal, a hemiketal, an acetal, or a ketal.

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Textbook Question

Glucose is the major sugar in mammalian blood. We often see it represented as either the "free aldehyde" or the cyclic hemiacetal forms shown here. Of the two forms of glucose, the cyclic hemiacetal is the preferred form found in blood. Can you suggest two reasons why?

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Textbook Question

Write the structures of the hemiacetal or hemiketal that result from reactions (a) and (b). Write the structures of the complete hydrolysis products of the acetal or ketal in (c) and (d).

a. Acetone + Ethanol → ?

618

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Textbook Question

What two products result from the complete hydrolysis of this cyclic acetal?

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Multiple Choice

What would be the product of the following reaction?

1053

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Multiple Choice

Draw the intermediate in the following reaction.