Question

Ionic reactions with organic compounds proceed through:
(A) Homolytic bond cleavage
(B) Heterolytic bond cleavage
(C) Free radical formation
(D) Primary free radical
(E) Secondary free radical
Choose the correct answer from the options given below:

• (A) only
• (C) only
• (B) only
• (D) and (E) only

Answer 1

The Correct Option is C

The question requires identifying the fundamental mechanism by which ionic reactions involving organic compounds proceed, from the provided choices.

Concept Used:

Organic reactions are categorized based on the manner in which covalent bonds break. Two principal types of covalent bond cleavage exist:

1. Homolytic Bond Cleavage (Homolysis): In this process, the shared electron pair in a covalent bond divides equally between the two separating atoms. This results in the formation of highly reactive, neutral species with an unpaired electron, termed free radicals. \[ \text{A:B} \xrightarrow{\text{Homolysis}} \text{A}^\bullet + \text{B}^\bullet \] Reactions involving this cleavage are designated as free-radical reactions.
2. Heterolytic Bond Cleavage (Heterolysis): In this process, the shared electron pair is entirely transferred to one of the bonded atoms upon bond rupture. This yields a pair of oppositely charged ions: a cation and an anion. \[ \text{A:B} \xrightarrow{\text{Heterolysis}} \text{A}^+ + \text{:B}^- \quad (\text{if B is more electronegative}) \] Reactions involving the generation and reaction of these charged species (ions) are known as ionic reactions.

Step-by-Step Solution:

Step 1: Analyze the term "Ionic Reactions".

By definition, an "ionic reaction" is one that proceeds via ionic intermediates. These intermediates are charged entities, such as carbocations (positively charged carbon atoms) or carbanions (negatively charged carbon atoms).

Step 2: Evaluate the bond cleavage necessary for ionic reactions.

For an ionic reaction to occur, charged intermediates must be generated from a neutral organic molecule. This necessitates the unequal rupture of a covalent bond, whereby one atom retains the entire bonding electron pair, becoming an anion, and the other atom loses the electrons, becoming a cation. This process is, by definition, heterolytic bond cleavage.

Step 3: Evaluate the provided options.

• (A) Homolytic bond cleavage: This process produces free radicals, not ions, and is foundational to free-radical reactions.
• (B) Heterolytic bond cleavage: This process generates ions (cations and anions), which are the critical intermediates in ionic reactions. This is the correct mechanism.
• (C) Free radical formation: Free radicals result from homolytic cleavage and are characteristic of free-radical reactions.
• (D) Primary free radical: This is a specific type of free radical, an intermediate in free-radical reactions.
• (E) Secondary free radical: This is also a specific type of free radical, an intermediate in free-radical reactions.

Consequently, options (A), (C), (D), and (E) are associated with free-radical mechanisms, whereas only option (B) accurately describes the bond-breaking mechanism essential for ionic reactions.

Final Result:

Ionic reactions are characterized by the involvement of charged intermediates (ions). The generation of these ions from covalent organic compounds occurs through the unequal breaking of a bond, termed heterolytic bond cleavage.

The correct answer is (B) Heterolytic bond cleavage.