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

What is the Relationship Between Isomers?

Organic Chemistry

5. Chirality

What is the Relationship Between Isomers?

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2:49 minutes

Problem 73a,b

Textbook Question

Draw the structure for a compound with molecular formula C₂H₂I₂F₂
a. that is optically inactive because it does not have an asymmetric center.
b. that is optically inactive because it is a meso compound.

Verified step by step guidance

Step 1: Understand the molecular formula C2H2I2F2. This indicates the compound contains 2 carbon atoms, 2 hydrogen atoms, 2 iodine atoms, and 2 fluorine atoms. The task is to draw two different structures based on optical inactivity criteria.

Step 2: For part (a), identify a structure that is optically inactive due to the absence of an asymmetric center. An asymmetric center is a carbon atom bonded to four different groups. To ensure optical inactivity, arrange the substituents (I, F, H) symmetrically around the two carbon atoms, such that neither carbon atom has four different groups attached.

Step 3: For part (b), identify a structure that is optically inactive because it is a meso compound. A meso compound has multiple stereocenters but possesses an internal plane of symmetry, making it optically inactive. Arrange the substituents (I, F, H) around the two carbon atoms such that the molecule has stereocenters but also an internal plane of symmetry.

Step 4: Draw the structure for part (a). Place the two carbon atoms in the center, and attach the substituents symmetrically (e.g., one iodine and one fluorine on each carbon atom, with hydrogens completing the bonds). Ensure no asymmetric centers are present.

Step 5: Draw the structure for part (b). Place the two carbon atoms in the center, and arrange the substituents (e.g., one iodine and one fluorine on each carbon atom) such that the molecule has stereocenters but also an internal plane of symmetry. Verify that the structure meets the criteria for a meso compound.

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Key Concepts

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

Optical Activity

Optical activity refers to the ability of a compound to rotate plane-polarized light. This property is typically observed in chiral molecules, which possess an asymmetric center (a carbon atom bonded to four different groups). Compounds that are optically inactive either lack chirality or have a specific symmetry that cancels out their optical activity.

Chirality and Asymmetric Centers

Chirality is a geometric property of some molecules that makes them non-superimposable on their mirror images, akin to left and right hands. An asymmetric center, usually a carbon atom, is bonded to four distinct substituents, leading to two enantiomers. A compound without an asymmetric center cannot exhibit optical activity, making it optically inactive.

Meso Compounds

Meso compounds are a specific type of stereoisomer that contain multiple chiral centers but are achiral due to an internal plane of symmetry. This symmetry results in the cancellation of optical activity, even though the compound has chiral centers. Meso compounds are important in understanding how molecular symmetry influences optical properties.

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Related Practice

Textbook Question

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

(h)

Textbook Question

Make a model and draw a three-dimensional structure for each compound. Then draw the mirror image of your original structure and determine whether the mirror image is the same compound. Label each structure as being chiral or achiral, and label pairs of enantiomers.

(e)

(f)

Textbook Question

For the molecules shown,

(i) count the number of stereocenters present and

(ii) draw all possible stereoisomers.

(iii) Identify the relationships between stereoisomers as enantiomers or diastereomers.

(a)

Textbook Question

(i) Which of the following pairs of compounds would you expect to have different physical properties?

(ii) What is the relationship between each of the pairs?

(iii) Assign the absolute configuration of each stereocenter to confirm your answer.