Problem 47 - A Complete Resource Book in Chemistry for JEE Main

Question

The compound that will not give iodoform on treatment with alkali and iodine is (a) Acetone (b) Ethanol (c) Diethyl ketone (d) isopropyl alcohol

Step-by-Step Solution

Answer

Diethyl ketone will not give iodoform reaction.

Step 1: Understanding Iodoform Reaction

Iodoform reaction occurs when methyl ketones or other compounds with the structure R-CO-CH3 are treated with iodine and an alkali. Compounds with the structure CH3CH(OH)- or those convertible to this structure by oxidation, like secondary alcohols, also give this reaction.

Step 2: Analyzing Each Option

Review each option: - **Acetone**: Contains a methyl ketone group. Will give iodoform test. - **Ethanol**: Can be oxidized to acetaldehyde (a methyl ketone), thus it gives iodoform. - **Diethyl ketone (3-pentanone)**: Does not have the CH3CO- group essential for the iodoform test. - **Isopropyl alcohol**: Can be oxidized to acetone (a methyl ketone), so it gives iodoform test.

Step 3: Determining the Exception

Diethyl ketone (3-pentanone) lacks the necessary CH3CO- structure required for the iodoform reaction. Thus, it is the compound that will not give the iodoform reaction.

Key Concepts

Methyl Ketones

Methyl ketones are a category of organic compounds characterized by the presence of a carbonyl group ( CO) that is directly bonded to a methyl group (CH3). This structural group is essential for various chemical reactions, notably the iodoform reaction. Methyl ketones have the general formula R-CO-CH3, where R represents an alkyl or aryl group. Their presence is critical in identifying chemical behaviors and reactivity in various reactions.

• In the iodoform test, methyl ketones react with iodine in the presence of a base, such as sodium hydroxide, to form a yellow precipitate called iodoform.
• This reaction is used to identify the presence of methyl ketones in a given compound.

The example of acetone (CH3COCH3) utilized in the iodoform test signifies its ability to produce iodoform due to its methyl ketone structure.

Oxidation of Alcohols

Oxidation of alcohols is a vital process in organic chemistry used to transform alcohols into more reactive compounds like aldehydes, ketones, and carboxylic acids. This conversion is particularly important when conducting the iodoform test, as certain alcohols can be oxidized into methyl ketones. There are two main transformations depending on the type of alcohol:

• **Primary Alcohols**: Oxidized usually to aldehydes, then to carboxylic acids. Ethanol, for instance, can be oxidized to acetaldehyde, a methyl ketone, thus participating in the iodoform reaction.
• **Secondary Alcohols**: Such as isopropyl alcohol can directly form ketones upon oxidation. Isopropyl alcohol oxidizes to acetone, which is a methyl ketone and hence reactive in the iodoform test.

Understanding these reactions helps in predicting the outcome of chemical processes like the iodoform reaction.

Chemical Reactions

Chemical reactions are the processes that lead to the transformation of substances into new compounds. Key reactions, such as the iodoform reaction, illustrate how specific functional groups interact to produce distinct products. The iodoform reaction is one example where certain conditions are necessary:

• An oxidizing agent, like iodine, is required.
• An alkaline environment is typically needed, often provided by substances like sodium hydroxide.

During this reaction, compounds with specific structures, such as methyl ketones or alcohols that can be oxidized to methyl ketones, undergo chemical changes to produce yellow crystalline iodoform and other byproducts. Chemical reactions form the basis of organic synthesis and analysis, revealing much about the structural intricacies of the compounds involved.