Ch. 7 - Structure and Synthesis of Alkenes; Elimination

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 7 - Structure and Synthesis of Alkenes; Elimination

Problem 6a,b

Chapter 7, Problem 6a,b

1. Determine which of the following compounds show cis-trans isomerism.
2. Draw and name the cis and trans (or Z and E) isomers of those that do.
a. hex-3-ene
b.buta-1,3-diene

Verified step by step guidance

Step 1: Understand the concept of cis-trans isomerism. Cis-trans isomerism, also known as geometric isomerism, occurs in alkenes when there are two different groups attached to each carbon of the double bond. The 'cis' isomer has the same groups on the same side, while the 'trans' isomer has them on opposite sides.

Step 2: Analyze compound a, hex-3-ene. Identify the position of the double bond, which is between the third and fourth carbon atoms. Check if there are two different groups attached to each carbon of the double bond. If so, it can exhibit cis-trans isomerism.

Step 3: Analyze compound b, buta-1,3-diene. Note that this compound has two double bonds. For cis-trans isomerism to occur, focus on each double bond separately and check if there are two different groups attached to each carbon of the double bonds.

Step 4: For hex-3-ene, if it shows cis-trans isomerism, draw the structure of the 'cis' isomer with the larger groups on the same side of the double bond and the 'trans' isomer with the larger groups on opposite sides. Name them accordingly.

Step 5: For buta-1,3-diene, determine if either of the double bonds can exhibit cis-trans isomerism. If so, draw and name the possible isomers, considering the arrangement of groups around each double bond.

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Key Concepts

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

Cis-Trans Isomerism

Cis-trans isomerism, also known as geometric isomerism, occurs in compounds with restricted rotation around a bond, typically a double bond. It requires two different groups attached to each carbon of the double bond. 'Cis' indicates that similar groups are on the same side, while 'trans' means they are on opposite sides.

Z and E Nomenclature

The Z and E nomenclature is used to describe the stereochemistry of double bonds when there are more than two substituents. 'Z' (from German 'zusammen') means the higher priority groups are on the same side, while 'E' (from German 'entgegen') indicates they are on opposite sides. Priority is determined by the Cahn-Ingold-Prelog rules.

Double Bond Structure

A double bond consists of one sigma and one pi bond, restricting rotation and allowing for isomerism. For cis-trans isomerism to occur, each carbon in the double bond must have two different substituents. In hex-3-ene, the double bond at the third position allows for cis-trans isomerism, while buta-1,3-diene does not due to its conjugated system.

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Related Practice

Textbook Question

Give the systematic (IUPAC) names of the following alkenes.

(d)

(e)

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Textbook Question

1. Determine which of the following compounds show cis-trans isomerism.

2. Draw and name the cis and trans (or Z and E) isomers of those that do.

c. hexa-2,4-diene

d. 3-methylpent-2-ene

Textbook Question

The following names are all incorrect. Draw the structure represented by the incorrect name (or a consistent structure if the name is ambiguous), and give your drawing the correct name.

a. cis-dimethylpent-2-ene

b. 3-vinylhex-4-ene

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Textbook Question

Give the systematic (IUPAC) names of the following alkenes.

(a)

(b)

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Textbook Question

Give the systematic (IUPAC) names of the following alkenes.

(f)

(g)