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Basics of Organic Chemistry question

2004 · Shift 0 · Q12
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Basics of Organic Chemistry question

2004 · Shift 0 · Q12

JEE MainChemistryBasics of Organic ChemistryMCQ+4 / −1
Which of the following will have meso-isomer also?
  1. A
    2- chlorobutane
  2. B
    2- hydroxyopanoic acid
  3. C
    2,3 – dichloropentane
  4. D
    2-3- dichlorobutane
View written solutionFree

Correct answer: D

  1. Condition for a meso compound

A meso compound must have:

  • at least two stereocentres, and
  • an internal plane of symmetry so that the molecule is achiral despite having stereocentres.

So we check each option for these two requirements.

  1. Option A: 2-chlorobutane

Structure: CH3−CH(Cl)−CH2−CH3\mathrm{CH_3-CH(Cl)-CH_2-CH_3}CH3​−CH(Cl)−CH2​−CH3​

  • Carbon-2 is a stereocentre.
  • There is only one chiral carbon.

A meso form is not possible with only one stereocentre.

So, A is not correct.

  1. Option B: 2-hydroxypropanoic acid

Structure: CH3−CH(OH)−COOH\mathrm{CH_3-CH(OH)-COOH}CH3​−CH(OH)−COOH

  • Carbon-2 is a stereocentre.
  • Again, there is only one chiral carbon.

Hence, no meso isomer is possible.

So, B is not correct.

  1. Option C: 2,3-dichloropentane

Structure: CH3−CH(Cl)−CH(Cl)−CH2−CH3\mathrm{CH_3-CH(Cl)-CH(Cl)-CH_2-CH_3}CH3​−CH(Cl)−CH(Cl)−CH2​−CH3​

  • Carbon-2 and carbon-3 are stereocentres.
  • But for meso form, the molecule must have internal symmetry.
  • Here the two ends are different:
    • one side has CH3\mathrm{CH_3}CH3​
    • the other side has CH2CH3\mathrm{CH_2CH_3}CH2​CH3​

So the molecule is not symmetrical and cannot have a plane of symmetry.

Hence, no meso isomer exists.

So, C is not correct.

  1. Option D: 2,3-dichlorobutane

Structure: CH3−CH(Cl)−CH(Cl)−CH3\mathrm{CH_3-CH(Cl)-CH(Cl)-CH_3}CH3​−CH(Cl)−CH(Cl)−CH3​

  • Carbon-2 and carbon-3 are stereocentres.
  • The molecule is symmetrical: both ends are CH3\mathrm{CH_3}CH3​.
  • Therefore, one stereoisomer with opposite configurations (2R,3S)(2R,3S)(2R,3S) or (2S,3R)(2S,3R)(2S,3R) has an internal plane of symmetry.

Thus, a meso isomer exists.

So, D is correct.

  1. Final answer

The compound which has a meso isomer is: D: 2,3-dichlorobutane\boxed{\text{D: 2,3-dichlorobutane}}D: 2,3-dichlorobutane​

  1. Comparison with stored correct answer

Stored correct answer: D

My derived answer: D

They match.

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