Question

The compound ' \(\mathrm{R}\) ' is (A) N, N-dimethylaniline (B) benzoic acid (C) \(p\)-cresol (D) benzaldehyde

Short answer

The compound R could be one of the following: (A) N, N-dimethylaniline \(\mathrm{C_{8}H_{11}N}\) - an aromatic amine with two methyl groups on the nitrogen atom. (B) Benzoic acid \(\mathrm{C_{7}H_{6}O_{2}}\) - an aromatic carboxylic acid. (C) \(p\)-cresol \(\mathrm{C_{7}H_{8}O}\) - an aromatic compound with a hydroxyl group and a methyl group in the para position. (D) Benzaldehyde \(\mathrm{C_{7}H_{6}O}\) - an aromatic compound with an aldehyde group. Without further information, we cannot definitively determine which compound R is.

Step-by-step solution

Identify compound A, N, N-dimethylaniline

N, N-dimethylaniline is an aromatic amine compound with the formula \(\mathrm{C_{8}H_{11}N}\). It consists of an aniline ring with two methyl groups attached to the nitrogen atom.

Identify compound B, benzoic acid

Benzoic acid is an aromatic carboxylic acid compound with the formula \(\mathrm{C_{7}H_{6}O_{2}}\). It features a carboxylic acid group attached to a benzene ring.

Identify compound C, p-cresol

\(p\)-cresol is an aromatic compound with the formula \(\mathrm{C_{7}H_{8}O}\). It consists of a benzene ring with a hydroxyl group and a methyl group at the para position (1,4 positions).

Identify compound D, benzaldehyde

Benzaldehyde is an aromatic compound with the formula \(\mathrm{C_{7}H_{6}O}\). It features an aldehyde group attached to a benzene ring. Based on the information provided, we are unable to determine the structure or formula of compound R. However, we can infer that R refers to one of the given options.

Key concepts

Aromatic Compounds

Aromatic compounds are a class of highly stable organic molecules known for their ring-like structure, called an aromatic ring. The most common type of aromatic ring is the benzene ring, which consists of six carbon atoms with alternating double and single bonds forming a hexagon. This unique bonding creates a delocalized system of electrons above and below the plane of the atoms, contributing to the ring's stability and reactivity.

One of the key features of aromatic compounds is their various types of substituents, which can alter the compound's properties. For example, p-cresol, one of the options in the exercise, includes a hydroxyl group and a methyl group at opposite ends of the benzene ring. The position of these substituents is significant in determining the compound's characteristics. The prefix 'p-' stands for para, indicating that the substituents are on opposite sides of the benzene ring, at the 1,4 positions.

Importance of Substituents in Aromatic Compounds

Giving context to the JEE Advanced exercise, understanding the nature of substituents on a benzene ring is crucial when predicting the chemical behavior and physical properties of aromatic compounds. It helps in distinguishing between molecules such as benzaldehyde, which contains an aldehyde group, and p-cresol, characterized by a hydroxyl group.

Carboxylic Acids

Carboxylic acids are organic compounds that contain a carboxyl group (-COOH), which consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group. This functional group is polar and can donate a proton (H+), which makes carboxylic acids acidic. Benzoic acid is an example of an aromatic carboxylic acid where the carboxyl group is attached directly to the benzene ring.

The acidic nature of carboxylic acids largely comes from the resonance stabilization of the carboxylate anion formed when the acid donates a proton. The resonance allows for the delocalization of the negative charge over two oxygen atoms, which lowers the energy of the molecule and stabilizes the anion.

Significance in Organic Synthesis

Carboxylic acids play a pivotal role in organic synthesis and biochemistry. In the context of the JEE Advanced examination, understanding the reactions and properties of carboxylic acids, like benzoic acid, is essential for predicting product formation and reaction mechanisms in organic chemistry.

Amines

Amines are organic compounds derived from ammonia (NH3) where one or more hydrogen atoms are replaced by alkyl or aryl groups. The structure of amines includes a nitrogen atom with a lone pair of electrons, making them basic. They can be categorized as primary, secondary, or tertiary amines, depending on the number of carbon-containing groups attached to the nitrogen. N, N-dimethylaniline is a tertiary aromatic amine, signified by the two methyl groups ((CH3)-N) and the aryl group (aniline).

The lone pair on the nitrogen allows amines to act as nucleophiles in chemical reactions, and their basicity is influenced by the substituents attached. In the case of N, N-dimethylaniline, the presence of the aromatic ring contributes to the molecule's overall reactivity and properties. For the JEE Advanced coursework, recognizing the structural features and functional behavior of amines is vital for deducing reaction outcomes and understanding their role in organic synthesis.

Understanding Amine Reactivity

In-depth knowledge of amines, including how electron-donating and electron-withdrawing groups affect their reactivity, is important for mastering organic chemistry topics. When tackling problems involving compounds like N, N-dimethylaniline, being aware of these concepts can greatly aid in predicting reaction mechanisms and understanding the molecule's behavior in various chemical environments.