Question

You are given four organic compounds “A”, “B” , “C” and “D”. The compounds “A”, “B” and “C” form an orange-red precipitate with 2, 4 DNP reagent. Compounds “A” and “B” reduce Tollen’s reagent while compounds “C” and “D” do not. Both “B” and “C” give a yellow precipitate when heated with iodine in the presence of NaOH. Compound “D” gives brisk effervescence with sodium bicarbonate solution. Identify “A”, “B”, “C” and “D” given the number of carbon atoms in three of these carbon compounds is three while one has two carbon atoms. Give an explanation for our answer.

Answer 1

A, B and C contain carbonyl group as they give positive 2, 4 DNP test

A and B are aldehydes as aldehydes reduce Tollen’s reagent

C is a ketone, as it contains carbonyl group but does not give positive Tollen’s test

C is a methyl ketone as it gives positive iodoform test

B is an aldehyde that gives positive iodoform test

D is a carboxylic acid

Since the number of carbons in the compounds A, B, C and D is three or two

B is CH₃CHO as this is only aldehyde which gives a positive iodoform test

The remaining compounds A, C and D have three carbons

A is \[\ce{CH3CH2CHO}\], C is \[\ce{CH3COCH3}\] and D is \[\ce{CH3CH2COOH}\]