Heterolytic bond dissociation energy of alkyl halides follows the sequence

Options

A. `R-F gt R -Cl gt R -Br gt R -I`
B. `R - I gt R - Br gt R - Cl gt R - F`
C. `R - I gt R - F gt R - Br gt R - Cl`
D. `R - Cl gt R - Br gt R- I gt R - F`

Explanation

To determine the heterolytic bond dissociation energy of alkyl halides, we need to analyze the bond strengths of the carbon-halogen bonds in various alkyl halides. The bond dissociation energy is influenced by the type of overlap between the orbitals of carbon and the halogen atoms.

### Step-by-Step Solution:

1. **Identify the Alkyl Halides**: The alkyl halides we are considering are those containing the halogens fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

2. **Understand the Bonding**: The carbon (C) atom forms bonds with halogen atoms through overlapping of their atomic orbitals. The types of overlaps are:
- C-F: Carbon 2p and Fluorine 2p
- C-Cl: Carbon 2p and Chlorine 3p
- C-Br: Carbon 2p and Bromine 4p
- C-I: Carbon 2p and Iodine 5p

3. **Analyze the Overlap Strength**: The strength of the bond is determined by the type of overlap:
- 2p-2p overlap (C-F) is stronger than 2p-3p overlap (C-Cl).
- 2p-3p overlap (C-Cl) is stronger than 2p-4p overlap (C-Br).
- 2p-4p overlap (C-Br) is stronger than 2p-5p overlap (C-I).

4. **Rank the Bond Dissociation Energies**: Based on the overlap strengths, we can rank the bond dissociation energies from highest to lowest:
- C-F bond has the highest bond dissociation energy.
- C-Cl bond is next.
- C-Br bond follows.
- C-I bond has the lowest bond dissociation energy.

5. **Conclusion**: The order of heterolytic bond dissociation energy for alkyl halides is:
\[ \text{C-F} > \text{C-Cl} > \text{C-Br} > \text{C-I} \]

### Final Answer:
The heterolytic bond dissociation energy of alkyl halides follows the sequence:
\[ \text{C-F} > \text{C-Cl} > \text{C-Br} > \text{C-I} \]