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

5. Chirality

Constitutional Isomers vs. Stereoisomers

Organic Chemistry

5. Chirality

Constitutional Isomers vs. Stereoisomers

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4:39 minutes

Problem 50

Textbook Question

(a) Give the products expected when (+)-glyceraldehyde reacts with HCN.
(b) What is the relationship between the products? How might they be separated?
(c) Are the products optically active? Explain.

Verified step by step guidance

Step 1: Understand the reaction of (+)-glyceraldehyde with HCN. (+)-Glyceraldehyde is an aldehyde with a hydroxyl group on the second carbon. When it reacts with HCN, the cyanide ion (CN⁻) acts as a nucleophile and attacks the carbonyl carbon of the aldehyde group, forming a cyanohydrin. This reaction creates a new chiral center at the carbon that was originally part of the carbonyl group.

Step 2: Predict the products. Since the attack of the cyanide ion on the planar carbonyl group can occur from either side, two stereoisomers (enantiomers) of the cyanohydrin will be formed. These enantiomers are mirror images of each other and are non-superimposable.

Step 3: Determine the relationship between the products. The two products are enantiomers, which means they are stereoisomers that are mirror images of each other. Enantiomers have identical physical properties (e.g., boiling point, melting point) except for their interaction with plane-polarized light and their behavior in a chiral environment.

Step 4: Discuss how the products might be separated. Since the products are enantiomers, they can be separated using chiral resolution techniques. One common method is to react the mixture with a chiral resolving agent to form diastereomers, which have different physical properties and can be separated by conventional methods such as crystallization or chromatography.

Step 5: Address optical activity of the products. Each individual enantiomer is optically active because it can rotate plane-polarized light. However, if the reaction produces an equal mixture of the two enantiomers (a racemic mixture), the optical activities of the enantiomers cancel each other out, and the mixture as a whole will not be optically active.

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Key Concepts

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

Nucleophilic Addition

Nucleophilic addition is a fundamental reaction in organic chemistry where a nucleophile attacks an electrophilic carbon atom, leading to the formation of a new bond. In the case of glyceraldehyde reacting with HCN, the cyanide ion (CN-) acts as the nucleophile, attacking the carbonyl carbon of glyceraldehyde, resulting in the formation of a cyanohydrin.

Stereochemistry and Optical Activity

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. The products of the reaction between glyceraldehyde and HCN can lead to the formation of chiral centers, which can result in optical isomers (enantiomers). Optical activity is the ability of a compound to rotate plane-polarized light, a property that is significant for chiral molecules.

Separation Techniques

Separation techniques are methods used to isolate and purify compounds from a mixture. In the context of the products formed from glyceraldehyde and HCN, techniques such as chromatography or recrystallization can be employed to separate the resulting cyanohydrin products based on their differing physical properties, such as solubility or polarity.

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Related Practice

Textbook Question

Draw a three-dimensional structure for each compound, and star all asymmetric carbon atoms. Draw the mirror for each structure, and state whether you have drawn a pair of enantiomers or just the same molecule twice. Build molecular models of any of these examples that seem difficult to you.

(e) chlorocyclohexane

(f) cis-1,2-dichlorocyclobutane

Textbook Question

For each pair, give the relationship between the two compounds. Making models will be helpful.

(a) (2R,3S)-2,3-dibromohexane and (2S,3R)-2,3-dibromohexane

(b) (2R,3S)-2,3-dibromohexane and (2R,3R)-2,3-dibromohexane

Textbook Question

For the compound 1-ethyl-3-isopropylcyclopentane,

(b) What is the stereochemical relationship between the cis isomers?

Textbook Question

(a) Give the products expected when (+)@glyceraldehyde reacts with HCN.(b) What is the relationship between the products? How might they be separated?(c) Are the products optically active? Explain.

Textbook Question

For the compound 1-ethyl-3-isopropylcyclopentane,

(d) LOOKING AHEAD What is the relationship between a cis isomer and a trans isomer?

Textbook Question

How many stereoisomers are possible for the following alkenes?

(c)

Textbook Question

b. Draw the six stereoisomers of octa-2,4,6-triene. Explain why there are only six stereoisomers, rather than the eight we might expect for a compound with three stereogenic double bonds.

Textbook Question

Draw the six stereoisomers of octa-2,4,6-triene. Explain why there are only six stereoisomers, rather than the eight we might expect for a compound with three stereogenic double bonds.

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(a) Give the products expected when (+)-glyceraldehyde reacts with HCN.(b) What is the relationship between the products? How might they be separated?(c) Are the products optically active? Explain.

Key Concepts

Nucleophilic Addition

Stereochemistry and Optical Activity

Separation Techniques

Watch next

(a) Give the products expected when (+)-glyceraldehyde reacts with HCN.
(b) What is the relationship between the products? How might they be separated?
(c) Are the products optically active? Explain.