Question

For the following,
(i) I\(^-\)
(ii) Cl\(^-\)
(iii) Br\(^-\)
the increasing order of nucleophilicity would be

• A. Br\(^-\) < Cl\(^-\) < I\(^-\)
• B. I\(^-\) < Cl\(^-\) < Br\(^-\)
• C. Cl\(^-\) < Br\(^-\) < I\(^-\)
• D. I\(^-\) < Br\(^-\) < Cl\(^-\)

Hint:

Nucleophilicity and basicity do not always follow the same trend. In protic solvents, larger halides are better nucleophiles despite being weaker bases.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Nucleophilicity is the ability of a species to donate an electron pair. For halide ions in protic solvents, nucleophilicity follows the order: I\(^-\) > Br\(^-\) > Cl\(^-\).

Step 2: Detailed Explanation:
In protic solvents (like water or alcohols), nucleophilicity increases down the group for halide ions. This is because the smaller ions (F\(^-\), Cl\(^-\)) are more strongly solvated by hydrogen bonding, making them less available for nucleophilic attack. I\(^-\) is the least solvated and thus the best nucleophile. The order of nucleophilicity in protic solvents is: \[ \text{I}^- > \text{Br}^- > \text{Cl}^- \] Therefore, the increasing order is Cl\(^-\) < Br\(^-\) < I\(^-\).

Step 3: Final Answer:
The correct increasing order is Cl\(^-\) < Br\(^-\) < I\(^-\), which corresponds to option (C).