Question

An unknown compound, known to contain three carbon atoms, yields the following results. Classify the alcohol:

1. DNPH test: negative
    Dichromate test: negative
    Iodoform test: negative

(1

Answer 1

DNPH test : It is the test for the presence of aldehydes/ketones (carbonyl compounds) but alcohols does not react with DNP reagent. Hence unknown alcohol compound shows negative test.

Dichromate test: Acidified potassium dichromate test is used to distinguish the different alcohols. Dichromate oxidise the primary alcohols to aldehydes and on further oxidation produce carboxylic acids whereas secondary alcohols undergo oxidation and produce ketones.

Tertiary alcohols do not undergo oxidation reaction because hydrogen atoms are not attached to the carbon atom to oxidise.

Iodoform test : It is the test used to test the carbonyl compounds, also secondary alcohol whereas tertiary alcohols and primary alcohol except ethanol give positive test.

Common alcohol that gives negative test for all the above tests is tertiary alcohol (C(CH₃₎₃OH), but the given number of carbon atoms is 3. There is no tertiary alcohol with 3 carbon atoms.