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

4. Alkanes and Cycloalkanes

Cis vs Trans

Organic Chemistry

4. Alkanes and Cycloalkanes

Cis vs Trans

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1:55 minutes

Problem 17b

Textbook Question

Which of the following cycloalkanes are capable of geometric (cis-trans) isomerism? Draw the cis and trans isomers.
b. 1-ethyl-3-methylcycloheptane

Verified step by step guidance

Step 1: Understand the concept of geometric (cis-trans) isomerism. Geometric isomerism occurs in cycloalkanes when there are two substituents on different carbon atoms of the ring, and these substituents can be positioned either on the same side (cis) or on opposite sides (trans) of the ring.

Step 2: Analyze the structure of 1-ethyl-3-methylcycloheptane. This compound has a cycloheptane ring with an ethyl group at the first carbon and a methyl group at the third carbon.

Step 3: Determine if the substituents allow for cis-trans isomerism. For geometric isomerism to occur, the substituents must be on different carbon atoms and the ring must be large enough to accommodate the spatial arrangement. Cycloheptane is large enough to allow for this isomerism.

Step 4: Draw the cis isomer. In the cis isomer, both the ethyl and methyl groups are on the same side of the cycloheptane ring. Visualize or sketch the ring with both substituents pointing in the same direction.

Step 5: Draw the trans isomer. In the trans isomer, the ethyl and methyl groups are on opposite sides of the cycloheptane ring. Visualize or sketch the ring with one substituent pointing up and the other pointing down, ensuring they are on opposite sides.

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Key Concepts

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

Geometric Isomerism

Geometric isomerism, also known as cis-trans isomerism, occurs in compounds with restricted rotation around a bond, typically a double bond or a ring structure. It requires two substituents on each side of the bond or ring, allowing for different spatial arrangements. In cycloalkanes, this isomerism arises when substituents are positioned differently relative to the ring plane.

Cycloalkane Structure

Cycloalkanes are saturated hydrocarbons with carbon atoms arranged in a ring. The ring structure restricts rotation, which can lead to geometric isomerism if substituents are present. The size and shape of the ring influence the stability and possibility of isomerism, with larger rings like cycloheptane being more flexible than smaller ones.

Substituent Positioning

In cycloalkanes, the positioning of substituents determines the possibility of cis-trans isomerism. For 1-ethyl-3-methylcycloheptane, the ethyl and methyl groups must be on different carbons and can be arranged either on the same side (cis) or opposite sides (trans) of the ring plane. This spatial arrangement affects the compound's physical and chemical properties.

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Related Practice

Textbook Question

Which of the following cycloalkanes are capable of geometric (cis-trans) isomerism? Draw the cis and trans isomers.

a. 3-ethyl-1,1-dimethylcyclohexane

Textbook Question

Which of the following cycloalkanes are capable of geometric (cis-trans) isomerism? Draw the cis and trans isomers.

c. 1-ethyl-3-methylcyclopentane

Textbook Question

Draw a structure for each compound (includes old and new names).

d. 1,3-cyclohexadiene

e. cycloocta-1,4-diene

f. (Z)-3-methyl-2-octene

Textbook Question

Determine which compounds show cis-trans isomerism. Draw and label the isomers, using both the cis-trans and E-Z nomenclatures where applicable.

a. pent-1-ene

b. pent-2-ene

Textbook Question

Draw the molecular orbital picture of trans-but-2-ene.

Textbook Question

Draw skeletal structures for the compounds in Problem 3, including any cis–trans isomers.

Textbook Question

Draw skeletal structures for the compounds in Problem 3, including any cis–trans isomers.

Textbook Question

a. Draw the condensed structures and give the systematic names for all the alkenes with molecular formula C₆H₁₂, ignoring stereoisomers. (Hint: There are 13.)

b. Which of the alkenes have E and Z isomers?

c. Which of the alkenes is the most stable?

d. Which of the alkenes is the least stable?

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