Question

\(2 \mathrm{CH}_{3}-\mathrm{CHO} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CHO}+\mathrm{H}_{2} \mathrm{O}\) The above reaction is catalysed by (a) bases only (b) acids only (c) both base and acid (d) \(\mathrm{P}_{2} \mathrm{O}_{5}\)

Short answer

Answer: (a) bases only

Step-by-step solution

1. Identify the reaction type

First, let's examine the given reaction: \(2 \mathrm{CH}_{3}-\mathrm{CHO} \longrightarrow \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CHO}+\mathrm{H}_{2} \mathrm{O}\). This is an organic chemistry reaction involving aldehyde molecules, and based on the molecular structure given, this appears to be a Cannizzaro reaction. In a Cannizzaro reaction, there is disproportionation of two aldehyde molecules to form an alcohol and a carboxylic acid salt when in the presence of a base catalyst.

2. Identify the suitable catalysts

For a Cannizzaro reaction, only a base catalyst will promote the necessary disproportionation. Therefore, the correct answer is: (a) bases only

Key concepts

Understanding Organic Chemistry

Organic chemistry is a branch of chemistry focused on the study of carbon-containing compounds. These compounds, which are generally known as organic compounds, include a vast range of substances that form the basis of all life on Earth.

Within organic chemistry, reactions are studied to understand how different organic molecules interact with one another. Aldehydes, a common organic functional group, are often central to many organic reactions. Aldehydes consist of a carbonyl center (a carbon double-bonded to oxygen) connected to a hydrogen atom and an R group, which can be anything from a simple hydrogen atom to complex rings or chains of carbon.

Understanding the structure and behavior of aldehydes is vital since they are readily reactive and can undergo a variety of chemical transformations. Reactions like the Cannizzaro reaction are a testament to the incredible diversity of organic chemical processes and their practical importance in fields ranging from pharmaceuticals to materials science.

The Reactivity of Aldehydes

Aldehydes are a crucial functional group in organic chemistry because of their high reactivity. This reactivity stems from the presence of the carbonyl group. Due to the electronegativity of the oxygen atom, the carbon in the carbonyl group is electrophilic, making it a target for nucleophilic attacks.

In particular environments, such as the presence of strong bases, aldehydes can participate in unique reactions, one of which is highlighted by the Cannizzaro reaction. Here, aldehydes undergo disproportionate to form an alcohol and a carboxylate salt. It's essential to recognize that not all aldehydes behave identically in reactions; their reactivity can be influenced by the nature of their R group as well as the reaction conditions.

The Role of Base Catalysts in Chemical Reactions

Base catalysts play a crucial role in organic chemistry by facilitating reactions that might otherwise proceed slowly or not at all. Catalysts, in general, lower the activation energy of a reaction, thus increasing the reaction rate without being consumed in the process.

A base catalyst, specifically, can provide electron density to the reaction environment, helping stabilize transition states and intermediates. This makes them particularly important for reactions involving proton transfer, such as deprotonation steps or the promotion of nucleophilic attacks. In the case of the Cannizzaro reaction, the base catalyst deprotonates one of the aldehyde molecules, enabling it to act as a nucleophile and attack another aldehyde molecule. This crucial step underscores the selective nature of catalysts and their role in directing the course of chemical reactions.