Question

In which pair, both the compounds show iodoform test? (a) Acetone and acetophenone (b) Acetophenone and benzophenone (c) Acetone and benzophenone (d) Ethanol and acetone

Short answer

Both ethanol and acetone in option (d) give a positive iodoform test.

Step-by-step solution

Identify the Iodoform Test Criteria

The iodoform test is used to identify methyl ketones or secondary alcohols with at least one methyl group (CH3) attached to the carbonyl carbon. Specifically, the compound must have either \( R-CO-CH_3 \) or \( CH_3CH(OH)R \) structure, where \( R \) can be a hydrocarbon chain.

Analyze Each Compound in Option (a)

Check the compounds in option (a): acetone (\( CH_3COCH_3 \)) is a methyl ketone, and thus shows the iodoform test. Acetophenone (\( C_6H_5COCH_3 \)) is also a methyl ketone and hence tests positive for the iodoform test.

Analyze Each Compound in Option (b)

For option (b), acetophenone (\( C_6H_5COCH_3 \)) will show a positive iodoform test. However, benzophenone (\( C_6H_5COC_6H_5 \)) lacks a methyl group connected to the carbonyl and thus will not give a positive iodoform test.

Analyze Each Compound in Option (c)

Option (c) includes acetone (\( CH_3COCH_3 \)) which shows a positive iodoform test. Benzophenone (\( C_6H_5COC_6H_5 \)), as noted before, does not show this test, failing the criteria for both compounds exhibiting the iodoform test.

Analyze Each Compound in Option (d)

In option (d), ethanol (\( CH_3CH_2OH \)) can undergo oxidation to form acetaldehyde (\( CH_3CHO \)), which will give a positive iodoform test due to the presence of the methyl group next to the carbonyl after oxidation. Acetone (\( CH_3COCH_3 \)) also gives a positive test as it is a methyl ketone. Both compounds fulfill the criteria.

Key concepts

Methyl Ketones

Methyl ketones are a specific type of ketones characterized by having a methyl group ( CH₃) directly attached to the carbonyl group. The general formula for methyl ketones is R-CO-CH₃, where R can be any hydrocarbon chain or aromatic ring. A familiar example is acetone ( CH₃COCH₃), which is one of the simplest methyl ketones and widely used as a solvent.

Methyl ketones are significant because they have a unique property that allows them to easily react in the iodoform test. This test is used to identify compounds that have a structure similar to methyl ketones or secondary alcohols capable of being oxidized to produce a methyl ketone structure. When treated with iodine ( I₂) and a base, such as sodium hydroxide ( NaOH), methyl ketones respond by forming a yellow precipitate known as iodoform ( CHI₃).

• Methyl ketones are characterized by the presence of a methyl group next to the carbonyl.
• They are largely identified through their positive reaction in the iodoform test.
• Acetophenone ( C₆H₅COCH₃) is an example that consists of both a methyl group and an aromatic ring around the carbonyl.

Recognizing these compounds is crucial in organic chemistry, especially when predicting or analyzing reactions that involve carbonyl containing structures.

Ethanol Oxidation

Ethanol ( CH₃CH₂OH) can undergo oxidation, a chemical reaction in which it loses electrons, leading to the formation of new compounds. Through this process, ethanol is converted into acetaldehyde ( CH₃CHO), a compound with a carbonyl group. This oxidation is typically carried out in the presence of an oxidizing agent, such as potassium dichromate ( K₂Cr₂O₇) in an acidic solution.

During ethanol oxidation, the alcohol group of ethanol ( −OH) is transformed into a carbonyl group ( =O), with the methyl group remaining intact. This transformation is crucial because acetaldehyde, the product of this reaction, possesses a methyl group near the carbonyl, fitting the criteria to produce a positive iodoform test result. This reaction is a key mechanism for demonstrating the relationship between different organic functional groups.

• Ethanol oxidation converts the OH group to a carbonyl group.
• Acetaldehyde formed can react positively in the iodoform test.
• The concept illustrates the interconnectedness of alcohols and aldehydes or ketones in organic chemistry.

Understanding ethanol oxidation deepens the comprehension of how simple alcohols can transform into more complex carbonyl compounds under specific conditions.

Carbonyl Compounds

Carbonyl compounds are organic compounds that contain a carbonyl group, C=O. These compounds hold a significant place in organic chemistry due to their wide range of chemical reactivity and their presence in many biological and synthetic materials.

The carbonyl group consists of a carbon atom double-bonded to an oxygen atom. The group can be part of different types of molecules, forming aldehydes, ketones, carboxylic acids, esters, and other derivatives. Aldehydes have the carbonyl group at the end of a carbon chain, while in ketones, the carbonyl group is bonded to two carbon atoms within the chain.

• Carbonyl compounds exhibit diverse chemical behavior due to the polar nature of the C=O bond.
• Their electrophilic carbon atom makes them susceptible to nucleophilic attack.
• Presence of the carbonyl group makes them participate in various reactions, such as oxidation-reduction and nucleophilic additions.

An understanding of carbonyl compounds is essential in chemistry, as these structures serve as starting points for synthesizing a wide range of chemical products. They also crucially illustrate how molecular structure affects chemical properties and reactivity, including reactions like the iodoform test.