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Basics of Organic Chemistry question

2020 · 6 Sep · Shift 1 · Q11
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Basics of Organic Chemistry question

2020 · 6 Sep · Shift 1 · Q11

JEE MainChemistryBasics of Organic ChemistryMCQ+4 / −1
Which of the following compounds shows geometrical isomerism?
  1. A
    2-methylpent-1-ene
  2. B
    4-methylpent-1-ene
  3. C
    2-methylpent-2-ene
  4. D
    4-methylpent-2-ene
View written solutionFree

Correct answer: D

  1. Condition for geometrical isomerism

A compound shows geometrical (cisciscis-transtranstrans / EEE-ZZZ) isomerism only if each carbon of the double bond has two different substituents.

If any one of the double-bonded carbons has two identical groups, geometrical isomerism is not possible.

  1. Check each option

Option A: 222-methylpent-111-ene

Structure:

CH2=C(CH3)−CH2−CH2−CH3CH_2=C(CH_3)-CH_2-CH_2-CH_3CH2​=C(CH3​)−CH2​−CH2​−CH3​

The first double-bond carbon is CH2CH_2CH2​, so it has two identical substituents: HHH and HHH.

Therefore, geometrical isomerism is not possible.

Option B: 444-methylpent-111-ene

Structure:

CH2=CH−CH2−CH(CH3)−CH3CH_2=CH-CH_2-CH(CH_3)-CH_3CH2​=CH−CH2​−CH(CH3​)−CH3​

Again, the first double-bond carbon is CH2CH_2CH2​, so it has two identical substituents: HHH and HHH.

Therefore, geometrical isomerism is not possible.

Option C: 222-methylpent-222-ene

Structure:

CH3−C(CH3)=CH−CH2−CH3CH_3-C(CH_3)=CH-CH_2-CH_3CH3​−C(CH3​)=CH−CH2​−CH3​

Now look at the left double-bond carbon:

  • it is attached to CH3CH_3CH3​ and another CH3CH_3CH3​
  • so it has two identical substituents

Therefore, geometrical isomerism is not possible.

Option D: 444-methylpent-222-ene

Structure:

CH3−CH=CH−CH(CH3)−CH3CH_3-CH=CH-CH(CH_3)-CH_3CH3​−CH=CH−CH(CH3​)−CH3​

Check the two double-bond carbons:

  • Left alkene carbon: attached to HHH and CH3CH_3CH3​
  • Right alkene carbon: attached to HHH and CH(CH3)CH3CH(CH_3)CH_3CH(CH3​)CH3​

Each double-bond carbon has two different substituents.

Therefore, geometrical isomerism is possible.

  1. Conclusion

Only Option D satisfies the condition for geometrical isomerism.

D: 4-methylpent-2-ene\boxed{\text{D: }4\text{-methylpent-2-ene}}D: 4-methylpent-2-ene​
  1. Comparison with stored correct answer

Stored correct answer: D

My derived answer: D

So, they agree.

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