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Aldehydes Ketones and Carboxylic Acids question

2021 · 17 Mar · Shift 1 · Q9
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Aldehydes Ketones and Carboxylic Acids question

2021 · 17 Mar · Shift 1 · Q9

JEE MainChemistryAldehydes Ketones and Carboxylic AcidsMCQ+4 / −1
Mesityl oxide is a common name of :
  1. A
    3-Methyl cyclohexane carbaldehyde
  2. B
    4-Methyl pent-3-en-2-one
  3. C
    2,4-Dimethyl pentan-3-one
  4. D
    2-Methyl cyclohexanone
View written solutionFree

Correct answer: B

  1. Recall what mesityl oxide is

Mesityl oxide is the common name of an α,β\alpha,\betaα,β-unsaturated ketone obtained by aldol condensation of acetone.

Its structure is:

CH3−CO−CH=C(CH3)−CH3\mathrm{CH_3-CO-CH=C(CH_3)-CH_3}CH3​−CO−CH=C(CH3​)−CH3​

  1. Write the IUPAC name

Let us number the longest chain containing the carbonyl carbon:

CH3−CO−CH=C(CH3)−CH3\mathrm{CH_3-CO-CH=C(CH_3)-CH_3}CH3​−CO−CH=C(CH3​)−CH3​

  • Total carbon chain: 5 carbons ⇒\Rightarrow⇒ pentanone framework
  • Carbonyl gets lowest locant: ketone at carbon 222
  • Double bond is between carbon 333 and carbon 444 ⇒\Rightarrow⇒ pent-333-en-222-one
  • There is a methyl substituent at carbon 444

So the IUPAC name is:

4-Methyl pent-3-en-2-one\boxed{4\text{-Methyl pent-3-en-2-one}}4-Methyl pent-3-en-2-one​

  1. Check the options
  • A: 333-Methyl cyclohexane carbaldehyde →\rightarrow→ aldehyde, not mesityl oxide
  • B: 444-Methyl pent-333-en-222-one →\rightarrow→ matches exactly
  • C: 2,42,42,4-Dimethyl pentan-333-one →\rightarrow→ saturated ketone, no double bond
  • D: 222-Methyl cyclohexanone →\rightarrow→ cyclic ketone, not mesityl oxide
  1. Conclusion

The correct option is:

B\boxed{\text{B}}B​

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