(a) An organic compound (A) having molecular formula C_{4}H_{8}O gives orange red precipitate with 2,4-DNP reagent. It does not reduce Tollens’ reagent but gives yellow precipitate of iodoform on heating with NaOH and I_{2}. Compound (A) on reduction with NaBH_{4} gives compound (B) which undergoes dehydration reaction on heating with conc.H_{2}SO_{4} to form compound (C). Compound (C) on Ozonolysis gives two molecules of ethanal.

Identify (A), (B) and (C) and write their structures. Write the reactions of compound (A) with (i) NaOH/I_{2} and (ii) NaBH_{4}.

(b) Give reasons :

(i) Oxidation of propanal is easier than propanone.

(ii) \alpha-hydrogen of aldehydes and ketones is acidic in nature.

 

 
 
 
 
 

Answers (1)

(a) A = CH3COCH2CH3

    B = CH3CHOHCH2CH3

    C = CH3CH=CHCH3

CH3COCH2CH3 \overset{NaOH+I_{2}}{\rightarrow} CHI3 + CH3CH2COONa

CH3COCH2CH3 \overset{NaBH_{4}}{\rightarrow}CH3CHOHCH2CH3

(b)

i)  Oxidation of propanal is easier than propanone because cleavage of C-H bond in propanal is easier than C-C bond in propanone.

ii) \alpha-hydrogen of aldehydes and ketones is acidic in nature due to resonance stabilization of conjugate base / enolate ion or structural representation.

 

 

 

 

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