Question

which term correctly describes the relative position of the two substituents on the benzene ring in the compound below?
chemical structure: cf₃ on benzene, and a group attached to the ring
○ trans
○ cis
○ ortho
○ para
○ meta
question 13 (10 points)
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which of the following cannot display cis - trans isomerism?
○ 2 - bromo - 3 - octene
○ 3 - pentene
○ 1 - heptene
○ 2 - methyl - 4 - nonene
○ all of these molecules can display cis - trans isomerism.

Explanation:

First Question (Benzene Substituent Position)

1. Recall the terms for benzene ring substituents:

• Ortho: substituents on adjacent (1,2) carbons.
• Meta: substituents on carbons with one carbon between them (1,3).
• Para: substituents on opposite (1,4) carbons.
• Cis/trans apply to alkenes/ring systems with restricted rotation, not benzene (which is planar with delocalized π - bonds, and the terms for benzene are ortho/meta/para).

1. In the given compound, the two substituents on the benzene ring are on adjacent carbons (1,2 - positions relative to each other). So the term is ortho. Trans and cis are not used for benzene substituents’ relative positions in this context. Meta is 1,3 and para is 1,4, which do not match here.

1. Cis - trans isomerism (geometric isomerism) in alkenes requires:

• A double bond (restricted rotation).
• Each carbon of the double bond has two different groups attached (so that swapping groups gives a different isomer).

1. Analyze each option:

• 2 - bromo - 3 - octene: The double bond is at C3 - C4. C3 has - Br and other groups, C4 has different groups. Satisfies conditions.
• 3 - pentene: The double bond is at C3 - C4. C3 has two different groups, C4 has two different groups (since it's pentene, structure is \( \text{CH}_3\text{CH}_2\text{CH}=\text{CHCH}_3 \)). Satisfies conditions.
• 1 - heptene: The double bond is at C1 - C2. The carbon C1 has two H atoms (since it's \( \text{H}_2\text{C}=\text{CHCH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_3 \)). So C1 has two identical groups (H), so no cis - trans isomerism.
• 2 - methyl - 4 - nonene: The double bond is at C4 - C5. C4 and C5 have different groups attached. Satisfies conditions.

Answer:

ortho

Second Question (Cis - Trans Isomerism)