The stability order of the given carbocations is :
`i. Cl_3C-CH_2^(o+)" "ii. F_3C-CH_2^(o+)" "iii. H_3C-CH_2^(o+)`

Options

A. i gt ii gt iii
B. iii gt i gt ii
C. iii gt ii gt i
D. ii gt iii gt i

Answer

To determine the stability order of the given carbocations, we will analyze each of the three carbocations based on the effects of the substituents attached to them.

### Step 1: Identify the Carbocations
We have three carbocations to analyze:
1. **Cl₃C-CH₂⁺** (trichloromethyl carbocation)
2. **F₃C-CH₂⁺** (trifluoromethyl carbocation)
3. **H₃C-CH₂⁺** (methyl carbocation)

### Step 2: Analyze the Effects of Substituents
- **Trichloromethyl Carbocation (Cl₃C-CH₂⁺)**:
- Chlorine is an electronegative atom and exhibits a -I (inductive) effect, withdrawing electron density from the carbocation. However, the -I effect of chlorine is weaker compared to fluorine.

- **Trifluoromethyl Carbocation (F₃C-CH₂⁺)**:
- Fluorine is more electronegative than chlorine and also exhibits a -I effect, which is stronger than that of chlorine. This means that the trifluoromethyl group will withdraw more electron density from the carbocation, making it less stable.

- **Methyl Carbocation (H₃C-CH₂⁺)**:
- The methyl group (H₃C) has a +I (inductive) effect, which means it donates electron density to the carbocation. Additionally, it can stabilize the carbocation through hyperconjugation, as there are three hydrogen atoms that can participate in hyperconjugation.

### Step 3: Compare the Stability
- The **trifluoromethyl carbocation (F₃C-CH₂⁺)** is the least stable due to the strong -I effect of three fluorine atoms, which significantly withdraws electron density from the positively charged carbon.

- The **trichloromethyl carbocation (Cl₃C-CH₂⁺)** is more stable than the trifluoromethyl carbocation but still less stable than the methyl carbocation due to the weaker -I effect of chlorine.

- The **methyl carbocation (H₃C-CH₂⁺)** is the most stable because it has a +I effect and can stabilize the positive charge through hyperconjugation.

### Conclusion: Stability Order
Based on the analysis:
- **Most Stable**: H₃C-CH₂⁺ (methyl carbocation)
- **Moderately Stable**: Cl₃C-CH₂⁺ (trichloromethyl carbocation)
- **Least Stable**: F₃C-CH₂⁺ (trifluoromethyl carbocation)

Thus, the stability order of the carbocations is:
**H₃C-CH₂⁺ > Cl₃C-CH₂⁺ > F₃C-CH₂⁺**