An alkene ‘A’ (Molecular formula C 5 H 10 ) on ozonolysis gives a mixture of two compounds ‘B’ and ‘C’. Compound ‘B’ gives positive Fehling’s test and also forms iodoform on treatment with iodine and NaOH solution. Compound ‘C’, does not give Fehling’s test but forms iodoform. Identify the compounds ‘A’, ‘B’ and ‘C’ giving suitable explanation and write the reactions of ozonolysis and iodoform formation from either ‘B’ or ‘C’. (5) OR Explain the reactivity of a-hydrogen atoms in ethanal. Write the reaction when (a) a mixture of ethanal and benzaldehyde is treated with NaOH (aq) and (b) when only benzaldehyde is treated with conc. KOH solution. Write the names of reaction in both the cases.

Question

Philoid · Accepted Answer

Molecular formula is C₅H₁₀ and compound B gives positive iodoform that means a –COCH₃ group is present and it is an aldehyde as it gives positive Fehling’s Test. Therefore, the compound B is CH₃CHO. So after ozonolysis the two compounds that are formed are

(2-Methylbut-2-ene) (ethanal) (propanone)

A- 2-Methylbut-2-ene

B- Ethanol

C- Propanone

OR

Ethanal has an alpha hydrogen which undergo aldol reaction to form a product. Due to the strong electron withdrawing effect of the carbonyl group and resonance stabilization of the conjugate base, the alpha hydrogens are acidic in nature.

a)

This reaction is known as the cross-canizzaro’s reaction.

b)

This type of reaction is the Cannizaro’s reaction.