Which alkyl halides react most readily by nucleophilic substitution ?

Options

A. ` CH_(3) CH_(2) Cl`
B. ` CH_(3) CH_(2) l `
C. `CH_(3) CH_(2) Br `
D. ` CH_(3) CH_(2) F `

Answer

To determine which alkyl halides react most readily by nucleophilic substitution, we need to consider a few key factors, including the nature of the alkyl halide, the leaving group ability, and the stability of the carbocation formed during the reaction.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Substitution**:
- Nucleophilic substitution involves a nucleophile attacking an electrophilic carbon atom in an alkyl halide, leading to the substitution of the halide group with the nucleophile.

2. **Identifying the Electrophilic Center**:
- The carbon atom bonded to the halogen (X) in the alkyl halide is the electrophilic center. This carbon is electron-deficient due to the electronegativity of the halogen.

3. **Evaluating Leaving Group Ability**:
- The ability of the halogen to leave is crucial. The order of leaving group ability is as follows:
- Iodide (I⁻) > Bromide (Br⁻) > Chloride (Cl⁻) > Fluoride (F⁻)
- Iodide is the best leaving group because it is larger and more stable as an ion compared to the other halides.

4. **Considering Carbocation Stability**:
- The stability of the carbocation formed during the reaction also affects the reaction rate. More stable carbocations (tertiary > secondary > primary) will form more readily.
- For example, a tertiary alkyl halide will form a more stable carbocation compared to a primary alkyl halide.

5. **Combining Factors**:
- Given that iodide is the best leaving group, alkyl halides that contain iodine will react most readily by nucleophilic substitution.
- Therefore, primary alkyl iodides will react quickly due to the excellent leaving group ability of iodide, while tertiary alkyl halides will also react readily due to the stability of the resulting carbocation.

6. **Conclusion**:
- The alkyl halides that react most readily by nucleophilic substitution are those with a good leaving group (iodide) and those that can stabilize the resulting carbocation effectively.

### Final Answer:
The alkyl halides that react most readily by nucleophilic substitution are those containing iodine, particularly primary alkyl iodides.

---