Answer the questions on the basis of passage given below:

As aldehydes & ketones possess the carbonyl functional group, they show similar reactions. They exhibit nucleophilic addition reactions, reduction, oxidations, reactions due to ∝-Hydrogen atom, and many other reactions, like Cannizzaro reaction to electrophilic substitution reactions (in case of aromatic aldehydes & ketones). These reactions help in the preparation of a number of important compounds, like acetic acid, vinyl acetate, polymers and in perfume and dye industries. Nucleophilic addition reactions form cyanohydrins. acetals, alcohols and N-substituted derivatives like imine, oxime, semicarbazone, phenylhydrazone & Schiff's base. Reactions due to ∝-hydrogen atoms help in formation of aldols and a, B-unsaturated aldehydes & ketones.

Out of the following compounds, which will give iodoform test

(A)    Isopropyl alcohol

(B)    Isobutyl alcohol

(C)    Secondary butyl alcohol

(D)   Ethyl alcohol

(E)    Acetic acid

Choose the correct answer from the options given below:

A, C, D

The correct answer is option (2) A, C, D.

The iodoform test is used to determine whether a given unknown chemical substance contains carbonyl compounds with an \(α-\)methyl group and the structural formula \((R-CO–CH_3)\) or alcohols with the formula \(R-CH(OH)-CH_3\). Iodine and aqueous sodium hydroxide \((NaOH)\) solution or potassium iodide \((KI)\) and sodium hypochlorite \((NaClO)\) solution can also be used to conduct the test. In the iodoform test, the unknown is let to react with a mixture of excess iodine and sodium hydroxide.

(A) Isopropyl alcohol:

Isopropyl alcohol on oxidation in the presence of chromic acid gives acetone, which gives a positive iodoform test.

(B) Isobutyl alcohol:

Isobutyl alcohol does not have an \(\alpha -methyl\) group so doesn't undergo an iodoform reaction.

(C) Secondary butyl alcohol:

Secondary butyl alcohol undergoes an iodoform test as it has an \(\alpha -methyl\)  group.

(D) Ethyl alcohol:

The only primary alcohol that provides the triiodomethane (iodoform) reaction is ethanol. If ‘R’ is a category of hydrocarbons, you have a secondary alcohol. This answer is provided by tonnes of secondary alcohols, but those that do all have a methyl group with the -OH group attached to the carbon.

(E) Acetic acid :

Acetic acid- is a carboxylic acid, that is, it has the \(−COOH\) bond. Due to delocalisation of electrons, there is presence of \(O\) adjacent to carbonyl. Therefore, acetic acid does not give iodoform test.