Problem 33 - A Complete Resource Book in Chemistry for JEE Main

Question

The ether that undergoes electrophilic substitution reaction is (a) \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{OC}_{2} \mathrm{H}_{5}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OCH}_{3}\)

Step-by-Step Solution

Answer

The ether that undergoes electrophilic substitution is (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OCH}_{3}\).

Step 1: Understanding Electrophilic Substitution

Electrophilic substitution reactions typically occur in aromatic compounds where an electrophile replaces a substituent on an aromatic ring. Given the structure of ethers, only ethers with an aromatic ring satisfy this condition.

Step 2: Analyzing Ether Structures

We need to identify which of the given compounds contain an aromatic ring. Looking at each option:(a) \(\mathrm{CH}_{3} \mathrm{OCH}_{3} \) does not, as it consists of only aliphatic (non-aromatic) groups. (b) \(\mathrm{CH}_{3} \mathrm{OC}_{2} \mathrm{H}_{5} \) also lacks an aromatic ring. (c) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5} \) consists entirely of aliphatic groups. (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OCH}_{3} \) contains a phenyl group \(\mathrm{C}_{6} \mathrm{H}_{5} \), which is aromatic.

Step 3: Identifying the Ether with Aromatic Ring

Among the given options, only \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OCH}_{3} \) contains an aromatic ring. Therefore, it is the only compound capable of undergoing electrophilic substitution due to its aromatic nature.

Step 4: Solution Conclusion

The ether that undergoes electrophilic substitution reaction is \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OCH}_{3} \), which is option (d), due to the presence of the aromatic phenyl group.

Key Concepts

Aromatic Compounds

Aromatic compounds are a fascinating group of chemicals characterized by a ring structure with alternating double and single bonds, known as aromatic rings. The most common example of an aromatic compound is benzene, which consists of six carbon atoms arranged in a ring, with each carbon atom also bonded to a hydrogen atom. The unique arrangement of the electrons in these rings provides aromatic compounds with exceptional chemical stability and makes them particularly receptive to certain reactions.
A key feature of aromatic compounds is their ability to undergo electrophilic substitution reactions. In these reactions, an electrophile — a positively charged or neutral species that seeks out electrons — replaces a hydrogen atom in the aromatic ring.

• The stability of the aromatic ring allows the compound to maintain its structure even after substitution.
• This characteristic reaction type is why aromatic compounds are integral to many chemical and biological processes.

Understanding the unique properties of aromatic compounds helps us appreciate their wide applications in industries ranging from pharmaceuticals to materials science.

Ethers

Ethers are a class of organic compounds that feature an oxygen atom connected to two alkyl or aryl groups. The general formula for ethers is \(R-O-R'\), where \(R\) and \(R'\) can be either the same or different carbon-containing groups. Ethers are characterized by their relatively low polarity, making them excellent solvents for a wide range of chemical reactions.
While ethers do not typically participate in electrophilic substitution themselves, they can contain aromatic groups that do. An example is anisole (phenyl methyl ether), represented by the formula \(\text{C}_{6}\text{H}_{5}\text{OCH}_{3}\). This compound consists of an aromatic ring bonded to an ether group, allowing it to undergo electrophilic substitution at the aromatic site while the ether functionality remains intact.

• Ethers are generally non-reactive under oxidizing conditions.
• They can, however, serve as a protective group in synthetic chemistry due to their non-participating nature in many reaction types.

Their versatility in being part of larger, reactive molecules like anisole enhances their value in organic synthesis and industrial applications.

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into different substances, involving changes in chemical structure and energy content. Among the myriad types of chemical reactions, electrophilic substitution is noteworthy for its role in modifying aromatic compounds.
Electrophilic substitution reactions involve the replacement of an atom, typically hydrogen, in an aromatic compound by an electrophile. The driving force for these reactions is the stability of the resulting compound and the aromatic ring's ability to withstand such modifications.

• Common electrophiles include ions or molecules such as \(\text{NO}_2^+\) (the nitronium ion) and \(\text{Cl}^+\) (chloronium ion).
• Reactions are often facilitated by catalysts like Lewis acids which enhance the reactivity of electrophiles.

These reactions are essential for introducing new functional groups into aromatic rings, which is a fundamental step in creating numerous complex chemical structures indispensable in drug development and material science. Understanding the principles behind these reactions enables chemists to design and synthesize a plethora of innovative compounds.