Question

The intermediates in heteropolar reactions are

• A. Free radicals only
• B. Cations only
• C. Anions only
• D. Both anions and cations

Hint:

Associate the prefixes with the type of fission and intermediates:

• \textbf{HOMO-} (meaning "same"): Homolytic fission \(\rightarrow\) electrons split the \textbf{same} way \(\rightarrow\) forms neutral \textbf{free radicals}.
• \textbf{HETERO-} (meaning "different"): Heterolytic fission \(\rightarrow\) electrons split a \textbf{different} way \(\rightarrow\) forms charged \textbf{ions} (cations and anions).

Answer 1

The Correct Option is D

Step 1: Understanding Bond Fission.
Chemical reactions involve the breaking of existing bonds and the formation of new bonds. The breaking of a covalent bond, known as bond fission, can occur in two ways:

• Homolytic Fission (Homolysis): The shared pair of electrons is distributed equally between the two separating atoms. This results in the formation of neutral species with an unpaired electron, called free radicals. These reactions are typically initiated by heat, light, or peroxides and are called homopolar reactions.
  Example: \( A:B \rightarrow A\cdot + \cdot B \)
  
• Heterolytic Fission (Heterolysis): The shared pair of electrons is transferred completely to one of the atoms. This results in the formation of a positively charged ion (cation) and a negatively charged ion (anion). This type of fission occurs in polar bonds and is often facilitated by polar solvents. Reactions involving these charged intermediates are called heteropolar reactions or ionic reactions.
  Example: \( A:B \rightarrow A^+ + :B^- \) (if B is more electronegative)

Step 2: Identifying Intermediates in Heteropolar Reactions.
As defined above, heteropolar reactions proceed through heterolytic bond fission. This process generates charged intermediates. Depending on which atom takes the electron pair, either a cation or an anion (or both, in different steps of a mechanism) can be formed as intermediates. For example, in electrophilic addition to an alkene, a carbocation is formed. In nucleophilic substitution, a carbocation (S\(_N\)1) or a transition state with developing charges is formed. In reactions involving carbanions, an anion is the intermediate. Therefore, the intermediates in heteropolar reactions are charged species, which can be either cations or anions.
Step 3: Final Answer.
The intermediates in heteropolar reactions are both anions and cations.