Problem 207 - A Complete Resource Book in Chemistry for JEE Main

Question

The structure of the compound that gives a tribromo derivative on treatment with bromine water is Cc1cccc(O)c1 OCc1ccccc1 [2006] (a) (b) (c) Cc1ccccc1O (d) Cc1ccc(O)cc1

Step-by-Step Solution

Answer

Compound (a) or (d) forms a tribromo derivative due to activated positions on the ring.

Step 1: Analyze the Question

We are asked to identify which compound yields a tribromo derivative when treated with bromine water. Bromine water typically adds to activated positions such as those adjacent to hydroxyl groups or alkyl substituents on aromatic rings.

Step 2: Understand Bromination

Bromination tends to occur at the ortho and para positions relative to electron-donating groups like -OH or -CH₃ on an aromatic ring. Compounds with multiple such positions will form polybromo derivatives.

Step 3: Review Each Compound

Examine each SMILES representation: Compound (a), Cc1cccc(O)c1, has a methyl group next to the hydroxyl. Compound (b), OCc1ccccc1, has no such activating methyl groups. Compound (c), Cc1ccccc1O, has the same structure as compound (a). Compound (d), Cc1ccc(O)cc1, resembles the structure in (a).

Step 4: Identify Major Product-Forming Compound

Compounds (a), (c), and (d) have aromatic rings activated by hydroxyl and methyl groups. These substituents activate multiple ortho and para positions, leading to tribromo derivatives.

Step 5: Determine Which Structure Aligns with the Named Structure

Compound (a) and compound (d) are identical, both leading to a tribromo derivative by having substituents that activate specific positions on the aromatic ring, enabling multiple bromination.

Key Concepts

Aromatic Compounds

Aromatic compounds are a fascinating class of molecules characterized by their unique ring structures and stability. These compounds typically consist of one or more benzene-like rings, which are arrangements of six carbon atoms bonded in a perfect hexagon. This hexagonal structure forms because of the delocalized π (pi) electrons, leading to resonance and incredible stability.
Many aromatic compounds are known for their pleasant smells, which is why they are named after the Greek word 'aroma.' In organic chemistry, benzene, with the formula \( C_6H_6 \), is the quintessential aromatic compound. Its stability and unique properties arise due to the overlapping of p orbitals, creating a ring of electrons above and below the plane of the carbon atoms.
You'll often find that aromatic compounds are the backbone of numerous pharmaceuticals, dyes, and plastics because of their chemistry. These compounds are not just structurally distinctive; they are also quite reactive under the right conditions, typically engaging in substitution reactions to maintain the ring's aromatic nature.

Electrophilic Aromatic Substitution

Electrophilic Aromatic Substitution (EAS) is a common and important reaction mechanism through which aromatic rings undergo functionalization. Instead of adding reagents to break the ring, these reactions substitute a hydrogen atom with an electrophile, preserving the aromatic ring's integrity.
In EAS, an electrophile, which is an electron-deficient species, attacks the electron-rich aromatic ring. The process typically involves several steps:

• Formation of the electrophile: This might involve generating a positively charged species from a precursor such as a halogen or nitrating agent.


• Attack on the aromatic ring: The electrophile forms a transient complex with the ring, temporarily disrupting the c6 system.


• Stabilization: A proton is lost, and the aromaticity is restored, completing the substitution.

An intriguing aspect of EAS is the influence of substituents already attached to the aromatic ring. Groups such as -OH and -CH₃ can activate the ring, making it more susceptible to substitution at the ortho and para positions, as seen in the problem where bromine adds to specific locations on the compound.

Organic Chemistry Reactions

In the realm of organic chemistry, understanding the various reactions that compounds can undergo is crucial. These reactions allow for the transformation and manipulation of organic molecules to create new compounds.
Some major types of reactions include:

• Substitution Reactions: Where an atom or group of atoms is replaced by another atom or group. Aromatic compounds often undergo electrophilic substitution as discussed earlier.


• Addition Reactions: Common in alkenes and alkynes, where atoms are added to the carbon-carbon multiple bonds without breaking the ring structure in aromatic systems.


• Elimination Reactions: Where atoms are removed from a molecule to form a double bond or triple bond, usually in non-aromatic compounds.


• Rearrangement Reactions: The structure of the molecule is rearranged to form isomers.

Each of these reaction types plays a pivotal role in organic chemistry, providing pathways for synthesizing complex molecules from simpler ones. Understanding these will enable you to predict and control chemical behavior, which is particularly important in the development of new materials and pharmaceuticals.