Question

The compound which disproportionate with conc. \(\mathrm{NaOH}\) is (A) \(\mathrm{CH}_{3} \mathrm{CHO}\) (B) \(\mathrm{Ph} \mathrm{CH}_{2} \mathrm{CHO}\) (C) HCHO (D) \(\mathrm{CH}_{3} \mathrm{COOH}\)

Short answer

The compound that disproportionates with concentrated NaOH is (B) \(\mathrm{Ph} \mathrm{CH}_{2} \mathrm{CHO}\) (benzyl aldehyde).

Step-by-step solution

Identify the functional groups

For each compound, we must identify the functional groups present to help us determine their oxidation states. (A) CH₃CHO → Aldehyde (Present in the CHO group) (B) PhCH₂CHO → Benzyl aldehyde (Benzyl group attached to an aldehyde) (C) HCHO → Formaldehyde (Aldehyde containing only hydrogen) (D) CH₃COOH → Carboxylic acid (COOH group)

Determine oxidation states

Now that we have identified the functional groups, let's determine the oxidation states of each compound: (A) CH₃CHO Aldehyde group (CHO): Oxidation state of central carbon is 1 (B) PhCH₂CHO Benzyl aldehyde: Oxidation state of central carbon (from benzyl group) is -1 Oxidation state of central carbon (from CHO group) is 1 (C) HCHO Formaldehyde: Oxidation state of central carbon is 0 (D) CH₃COOH Carboxylic acid group (COOH): Oxidation state of carbonyl carbon (C=O) is 3

Identify the compound that disproportionates with conc. NaOH

To find the compound that disproportionates, we want the one containing a carbon atom that can undergo both oxidation and reduction when reacted with concentrated NaOH. Compound (B) \(\mathrm{Ph} \mathrm{CH}_{2} \mathrm{CHO}\) has benzyl aldehyde group with a central carbon oxidation state of -1 (benzyl group) and 1 (aldehyde group). It means that in the reaction with concentrated NaOH, this compound can undergo both oxidation and reduction, fitting the requirement for disproportionation.

Conclusion

The compound which disproportionate with concentrated NaOH is (B) \(\mathrm{Ph} \mathrm{CH}_{2} \mathrm{CHO}\) (benzyl aldehyde).

Key concepts

Disproportionation Reaction

A disproportionation reaction is a special type of redox reaction where a single element undergoes both oxidation and reduction simultaneously. This means that the element in question experiences a change in its oxidation state by both gaining and losing electrons.
For example, if a compound can oxidize one part of its molecule while reducing another, it is capable of disproportionation.
Understanding this concept is crucial when predicting chemical behavior, especially in organic compounds, where identifying the right conditions and functional groups is key.

Oxidation States

Oxidation states, also known as oxidation numbers, represent the hypothetical charge that an atom would have if all bonds to atoms of different elements were completely ionic.

• They help in understanding the movement of electrons in a reaction.
• For organic molecules, carbon's oxidation state can greatly vary depending on attached atoms and functional groups.
• For instance, in the formaldehyde (\[ ext{HCHO}\]), the oxidation state of carbon is 0 since it is bonded to only hydrogen and oxygen atoms which have set oxidation states of +1 and -2 respectively.

Recognizing these states is vital to foresee how compounds will interact with oxidizing and reducing agents.

Aldehydes

Aldehydes are a class of organic compounds containing the functional group \[ ext{-CHO}\].
This group is crucial because it defines the reactivity of aldehydes, which can undergo oxidation and reduction based on their environment.

• For example, in benzyl aldehydes like \[ ext{PhCH}_2 ext{CHO}\], the presence of both benzyl and aldehyde groups creates varied redox opportunities.
• This makes them prime candidates for reactions like disproportionation.

Aldehydes often participate in fascinating chemical reactions, reflecting their dynamic role in organic chemistry.

Functional Groups

Functional groups are specific groupings of atoms within molecules that have characteristic chemical behaviors.
In organic chemistry, knowing functional groups allows you to predict and understand reactions.

• Aldehydes contain the \[ ext{-CHO}\] group, linking a carbon atom to both a hydrogen atom and a double bonded oxygen.
• Carboxylic acids, on the other hand, have a \[ ext{-COOH}\] group, responsible for their acidic properties.

Identifying functional groups helps in determining how a molecule interacts with other substances, crucial for predicting outcomes in chemical reactions like disproportionation.