(a) Write the structures of A, B, C, and D in the following reactions:

(b) Distinguish between the following:

(i)

(ii) Benzoic acid and phenol

OR

(a) Write the structures of the main products when ethanal reacts with the following reagents:

(i) HCN

(ii)

(iii) LiAlH₄

(b) Arrange the following in the increasing order of their activity towards nucleophilic addition reaction:

(c) Give a sample chemical test to distinguish between the following pair of compounds:

Benzoyl chloride on treatment with H₂ in presence of a poisoned catalyst Pd-BaSO₄, this reaction is called as Rosenmund reaction and the catalyst is called Lindlar’s catalyst. On reduction of benzoyl chloride we get benzaldehyde. The presence of BaSO₄ reduces the surface pores for H₂ and thus partial reduction takes place.

When benzaldehyde is treated with concentrated NaOH and then hydrolysed with water in acidic medium it undergoes simultaneous oxidation reduction to give an oxidised benzoic acid and reduced benzyl alcohol.

This reaction is called as Cannizaro reaction.

When benzaldehyde is treated with Grignard’s reagent followed by hydrolysis it gives secondary alcohol.

(b)

(i)

Methyl ketones can be easily identified with the help of haloform test. When methyl ketones are oxidised by sodium hypothalite to sodium salts of corresponding carboxylic acid acids having one carbon less and the methyl group is converted into haloform. These haloform have distinct smell that helps in qualitative analysis of the compound.

Thus can be distinguished by the help of haloform test.

(ii) Benzoic acid and phenol

Benzoic acids are stronger acids as compared to alcohols so they can be distinguished with the help of litmus test. Benzoic acid will turn litmus paper red whereas phenols cannot.

Another test is treatment with sodium bicarbonate.

When benzoic acid is treated with NaHCO₃, it undergoes neutralization to give sodium benzoate and CO₂ is evolved which turns the acid solution milky indicating presence of a carboxylic acid.

OR

(a)

(i) Ethanal or acetaldehyde when treated with HCN it undergoes nucleophilic addition reaction to give cyanohydrin as product.

(ii) ethanal when treated with hydrazine in acidic conditions gives corresponding hydrazine derivative.

(iii) when reduced using LiAlH₄, aldehydes give reduced alcohol, here ethanal on reduction gives ethanol

(b)

Nucleophilic addition involves the attack of nucleophile on the sp² hybridized carbon and the geometry shifts from sp² to sp³ i.e. from triangular planar to tetrahedral, this transition will always prefer modes of least stearic hindrance from the substituents.

So according to the above given examples the decreasing order of ones exhibiting hindrance is:

Thus the order of reactivity for nucleophilic addition is same as above.

(c)

Aldehydes and ketones containing atleast one methyl group attached to carbonyl group can be easily identified with the help of haloform test. When methyl ketones or aldehydes are oxidized by sodium hypothalite to form sodium salts of corresponding carboxylic acid acids that have one carbon less and the methyl group is converted into haloform. These haloform have distinct odor that helps detection in qualitative analysis of the compound.