Which of the following would be the best (most reactive) nucleophile in the polar medium?

Options

A. `I^(-)`
B. `Br^(-)`
C. `Cl^(-)`
D. `F^(-)`

Answer

To determine the best (most reactive) nucleophile in a polar medium, we can follow these steps:

### Step 1: Understand the Concept of Nucleophilicity
Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile. In polar media, the solvent can influence the reactivity of nucleophiles.

**Hint:** Nucleophilicity is influenced by both the solvent and the size of the nucleophile.

### Step 2: Identify the Type of Polar Medium
In this case, we are dealing with a polar protic medium. Polar protic solvents are those that can form hydrogen bonds, such as water (H2O) and alcohols (e.g., CH3OH).

**Hint:** Remember that polar protic solvents stabilize ions through solvation, which can affect nucleophilicity.

### Step 3: Analyze Nucleophilicity Trends in Polar Protic Solvents
In polar protic solvents, the nucleophilicity generally increases down a group in the periodic table. This is because larger ions are less solvated and can more easily donate their electron pairs.

**Hint:** Compare the size and charge of the nucleophiles to understand their reactivity.

### Step 4: Compare the Given Nucleophiles
Assuming we have the following nucleophiles: F-, Cl-, Br-, and I-.

- F-: Small size, highly solvated, least nucleophilic in polar protic.
- Cl-: Larger than F-, but still solvated.
- Br-: Larger than Cl-, less solvated than Cl-.
- I-: Largest of all, least solvated, most nucleophilic.

**Hint:** Larger ions are typically better nucleophiles in polar protic solvents.

### Step 5: Determine the Best Nucleophile
Based on the trends discussed, the order of nucleophilicity in polar protic solvents is:
I- > Br- > Cl- > F-

Thus, the best nucleophile in a polar medium is I- (iodide ion).

**Final Answer:** The best (most reactive) nucleophile in the polar medium is I-.