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

검증된 단계별 안내

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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주요 개념

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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.

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.

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.

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