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Ch.1 - Structure and Bonding
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.1 - Structure and BondingProblem 24a,b,c
Chapter 1, Problem 24a,b,c

Which of the following compounds show cis-trans isomerism? Draw the cis and trans isomers of those that do.
(a) CHF=CHF
(b) F2C=CH2
(c) CH2=CH–CH2–CH3

Verified step by step guidance
1
Step 1: Understand the concept of cis-trans isomerism. Cis-trans isomerism occurs in compounds with a double bond where two different groups are attached to each carbon atom of the double bond. The cis isomer has the same groups on the same side of the double bond, while the trans isomer has the same groups on opposite sides.
Step 2: Analyze compound (a) CHF=CHF. Each carbon atom in the double bond is attached to a hydrogen atom and a fluorine atom, which are different groups. This satisfies the condition for cis-trans isomerism. Draw the cis isomer with both fluorine atoms on the same side of the double bond and the trans isomer with fluorine atoms on opposite sides.
Step 3: Analyze compound (b) F2C=CH2. The carbon atom on the left is attached to two fluorine atoms, making it symmetrical. Since one carbon atom has identical groups, cis-trans isomerism is not possible for this compound.
Step 4: Analyze compound (c) CH2=CHCH2CH3. The carbon atom on the left is attached to two hydrogen atoms, making it symmetrical. Since one carbon atom has identical groups, cis-trans isomerism is not possible for this compound.
Step 5: Summarize the findings. Compound (a) CHF=CHF shows cis-trans isomerism, and its cis and trans isomers can be drawn. Compounds (b) F2C=CH2 and (c) CH2=CHCH2CH3 do not show cis-trans isomerism due to the presence of identical groups on one of the double-bonded carbon atoms.

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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 double bond or a ring structure. In cis isomers, substituents are on the same side of the double bond, while in trans isomers, they are on opposite sides. This type of isomerism can significantly affect the physical and chemical properties of the compounds.
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Alkenes and Double Bonds

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). The presence of this double bond is crucial for the possibility of cis-trans isomerism, as it restricts the rotation of the carbon atoms involved. Understanding the structure of alkenes helps in identifying which compounds can exhibit geometric isomerism.
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Substituents and Priority

In determining cis-trans isomerism, the nature and position of substituents on the carbon atoms involved in the double bond are essential. For a compound to exhibit cis-trans isomerism, each carbon in the double bond must have two different substituents. The arrangement of these substituents dictates whether the isomer is classified as cis or trans.
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Related Practice
Textbook Question

Give the relationship between the following pairs of structures. The possible relationships are:

same compound

constitutional isomers (structural isomers)

cis-trans isomers

not isomers (different molecular formula)


(a)

(b)

(c)

1328
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Textbook Question

Give the relationship between the following pairs of structures. The possible relationships are:

same compound

constitutional isomers (structural isomers)

cis-trans isomers

not isomers (different molecular formula)


(g) CH3–CH2–CH2–CH3 and CH3–CH=CH–CH3

(h) CH2=CH–CH2CH2CH3 and CH3–CH=CH–CH2CH3

(i) CH2=CHCH2CH2CH3 and CH3CH2CH2CH=CH2

1462
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Textbook Question

For each pair of structures, determine whether they represent different compounds or a single compound.

1442
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Textbook Question

Predict the hybridization, geometry, and bond angles for the carbon and nitrogen atoms in acetonitrile (CH3–C≡N:).

1501
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Textbook Question

Give the relationship between the following pairs of structures. The possible relationships are:

same compound

constitutional isomers (structural isomers)

cis-trans isomers

not isomers (different molecular formula)


(j)

(k)

1164
views
Textbook Question

Two compounds with the formula CH3–CH=N–CH3 are known.

b. What two compounds have this formula?

c. Explain why only one compound with the formula (CH3)2CNCH3 is known.

3017
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