Chemistry Class 12 NCERT Solutions: Chapter 12 Aldehydes Ketones and Carboxylic Acids Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q: 7. Which of the following compounds would undergo aldol condensation, which the Cannizzaro reaction and which neither? Write the structures of the expected products of aldol condensation and Cannizzaro reaction.

(i) Methanal

(ii) 2-Methylpentanal

(iii) Benzaldehyde

(iv) Benzophenone

(v) Cyclohexanone

(vi) 1-Phenylpropanone

(vii) Phenylacetaldehyde

(viii) Butan-1-ol

(ix) 2,2-Dimethylbutanal

Answer:

Aldehydes and ketones having at least one α-hydrogen undergo aldol condensation. The compounds (ii) 2 − methylpentanal, (v) cyclohexanone, (vi) 1-phenylpropanone, and (vii) Phenylacetaldehyde contain one or more α-hydrogen atoms. Therefore, these undergo aldol condensation.

Aldehydes having no α-hydrogen atoms undergo Cannizzaro reactions. The compounds (i) Methanal, (iii) Benzaldehyde, and (ix) 2,2-dimethylbutanal do not have any α-hydrogen. Therefore, these undergo cannizzaro reactions.

Compound (iv) Benzophenone is a ketone having no α-hydrogen atom and compound (viii) Butan-1-ol is an alcohol. Hence, these compounds do not undergo either aldol condensation or cannizzaro reactions.

Aldol Condensation:

(ii)

Q_7_Ans_ii_Adol Condensation

(v)

Q_7_Ans_v_Adol Condensation

(vi)

Q_7_Ans_vi_Adol Condensation

(vii)

Q_7_Ans_vii_Adol Condensation

Cannizzaro Reaction

(i)

Q_7_Ans_i_Cannizzaro Reaction

(iii)

Q_7_Ans_iii_Cannizzaro Reaction

(ix)

Q_7_Ans_ix_Cannizzaro Reaction

Q: 8. How will you convert ethanal into the following compounds?

(i)

(ii)

(iii)

Answer:

(i) On treatment with dilute alkali, ethanal produces 3-hydroxybutanal gives butane-1,3-diol on reduction.

(ii) On treatment with dilute alkali, ethanal gives 3-hydroxybutanal which on heating produces but-2-enal.

(iii)

When treated with Tollen՚s reagent, But-2-enal produced in the above reaction produces but-2-enoic acid.

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