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Aldehydes, Ketones, and Carboxylic Acids — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryAldehydes, Ketones, and Carboxylic Acids3 Marks
Question
Give reasons:
  1. Propanone is less reactive than ethanal towards nucleophilic addition reactions.
  2. $\ce{O_2N – CH_2 – COOH} $ has lower pKa value than $\ce{CH_3COOH}$.
  3. $\ce{(CH_3)_2CH – CHO}$ undergoes aldol condensation whereas $\ce{(CH_3)_3C – CHO}$ does not.
✓

Answer

  1. Due to steric hindrance and $+I$ effect caused by two alkyl groups in propanone.
  2. Due to electron withdrawing nature of $\ce{–NO_2}$ group which increases the acidic strength and decreases the $pK_a$ value.
  3. $\ce{(CH_3)_2CH-CHO}$ has one $\alpha - H$ atom whereas $\alpha - H$ atom is absent in $\ce{(CH_3)_{3 }C-CHO}$.

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