Question

Among the following which one does not act as an intermediate in Hoffinann rearrangement? (a) RNCO (b) RCO? (c) RCON?HBr (d) RNC

Short answer

Option (d) RNC is not an intermediate in the Hofmann rearrangement.

Step-by-step solution

Understanding the Hofmann Rearrangement

The Hofmann rearrangement is a chemical reaction that involves the conversion of a primary amide to a primary amine with one less carbon. The process typically involves the formation of an isocyanate (RNCO) as an intermediate.

Identify Possible Intermediates

The possible intermediates in a Hofmann rearrangement include: - Isocyanate (RNCO), which is formed during the reaction. - Carbamate intermediate, which is another form that can appear transiently. - Bromoamide (RCONHBr), which is not typically listed but is involved at some steps.

Analyze Each Option

Evaluate each given option: - (a) RNCO: This is an isocyanate, commonly produced as an intermediate in the Hofmann rearrangement. - (b) RCO: This formula resembles an acyl radical; however, it's not typical of Hofmann rearrangement intermediates. - (c) RCONHBr: Represents a bromoamide, involved in transitional steps during the reaction. - (d) RNC: This is known as isocyanide, which doesn't form during the Hofmann rearrangement process.

Conclusion: Identify the Non-Intermediate

Based on the analysis, option (d) RNC (isocyanide) does not participate as an intermediate in the Hofmann rearrangement because it is not typically formed at any stage of this reaction.

Key concepts

Primary Amide

A primary amide is an important organic compound with the functional group -CONH2. This structure consists of a carbonyl group (C=O) bonded to an NH2 group. Primary amides serve as the starting point in many chemical reactions and transformations, including the Hofmann rearrangement. Here, the amide undergoes a reaction that reduces it to a primary amine with one fewer carbon atom. In the molecular structure, amides are often derived from carboxylic acids, where the hydroxyl group is replaced by an amino group. Primary amides are intriguing due to their polar nature and distinct chemical behavior, making them a crucial element in organic chemistry and biochemical processes.

Primary Amine

In organic chemistry, a primary amine is a type of amine where one hydrogen atom in ammonia (NH3) is replaced with an alkyl or aryl group, giving the general formula RNH2. Primary amines are notable for their nucleophilic character, making them reactive in various chemical transformations.

During the Hofmann rearrangement, the resulting compound from the reaction is a primary amine. This transformation involves the migration of the carbon atom adjacent to the nitrogen in the amide group, effectively removing one carbon. The change from amide to amine involves a decarboxylation-like process that leaves the nitrogen with an alkyl or aryl group, thereby forming a primary amine. Primary amines are versatile in chemistry due to their ability to engage in diverse reactions, bonds, and complex formations with other molecules.

Isocyanate Intermediate

An isocyanate is a key intermediate in the Hofmann rearrangement, characterized by its functional group -NCO. During the rearrangement process, the primary amide is converted into an isocyanate, setting the stage for further chemical transformations.

The presence of the carbon atom in the N=C=O link is responsible for the compound's reactivity, often leading to various derivative reactions. In the Hofmann rearrangement, the isocyanate intermediate is transient but crucial, as it undergoes hydrolysis to form the end product, which is a primary amine. It's important to note that isocyanates are widely used in the production of polyurethanes and other materials due to their reactive nature. Understanding the role of the isocyanate intermediate provides deeper insight into the molecular mechanisms driving chemical reactions and syntheses.

Carbamate

A carbamate is a transitional compound that may appear in certain chemical reactions, such as the Hofmann rearrangement. It is formed by the reaction of an isocyanate with water or alcohols. Structurally, carbamates consist of an amide linkage (–NH-CO-O–), which can vary based on the specific substituents attached to the nitrogen or the carbon atoms.

In the context of the Hofmann rearrangement, the formation of a carbamate is part of the reaction pathway that leads to the final product, a primary amine. While not a stable long-term compound in this reaction, the carbamate intermediate plays an essential role as it gives rise to the eventual chemical breakdown and formation of the desired amine product. Carbamates are notable in chemistry and industry for their applications in pharmaceuticals, agriculture, and material sciences.

Bromoamide

A bromoamide is involved in the initial stages of the Hofmann rearrangement. This compound is characterized by the presence of a bromine atom attached to the amide group. It is formed when the primary amide reacts with a bromine source under basic conditions, often using sodium hydroxide as a catalyst. The structure can be represented as RCONHBr, where R is an organic radical.

In the Hofmann rearrangement, the bromoamide acts as a pivotal agent, enabling the formation of an isocyanate intermediate. Although not an end product, the creation and transformation of the bromoamide into other intermediate compounds highlight its importance in facilitating the rearrangement process. Understanding the role of bromoamides enhances comprehension of the reactivity and pathways involved in complex organic reactions.