Which of the following statements is/are CORRECT for `C Cl_(3)^(-)` and `:C Cl_(2)`

Options

A. back bonding in both cases from Cl to C-atom
B. Back bonding in both cases from C to Cl-atom
C. Back bonding in `C Cl_(3)^(-)` from c to Cl but reverse in `: C Cl_(2)`
D. Direction of back bonding is just opposite in two cases.

Answer

To determine which statements are correct for the species \( \text{CCl}_3^{-} \) and \( \text{CCl}_2 \), we will analyze their structures and the nature of back bonding in each case.

### Step 1: Draw the structures of the species
1. **For \( \text{CCl}_3^{-} \)**:
- Carbon (C) is the central atom.
- It is bonded to three chlorine (Cl) atoms.
- Since it has a negative charge, it has an extra electron.
- Each chlorine atom has three lone pairs.
- The structure can be represented as:
```
Cl
|
Cl - C - Cl
|
[−]
```

2. **For \( \text{CCl}_2 \)**:
- Carbon (C) is again the central atom.
- It is bonded to two chlorine (Cl) atoms.
- Each chlorine atom has three lone pairs, and carbon has one lone pair.
- The structure can be represented as:
```
Cl
|
Cl - C
|
(lone pair)
```

### Step 2: Analyze back bonding
1. **In \( \text{CCl}_3^{-} \)**:
- The back bonding occurs from the carbon atom to the chlorine atoms.
- The carbon atom donates its electron density into the empty p-orbitals of chlorine, which stabilizes the molecule.

2. **In \( \text{CCl}_2 \)**:
- The back bonding occurs from the lone pairs of chlorine atoms to the vacant p-orbitals of carbon.
- This means that the direction of back bonding is from chlorine to carbon.

### Step 3: Evaluate the statements
1. **Statement 1**: Back bonding in both cases is from chlorine to carbon.
- **Evaluation**: This is incorrect. In \( \text{CCl}_3^{-} \), back bonding is from carbon to chlorine, while in \( \text{CCl}_2 \), it is from chlorine to carbon.

2. **Statement 2**: Back bonding in both cases is from carbon to chlorine.
- **Evaluation**: This is also incorrect. The directions of back bonding are different in both cases.

3. **Statement 3**: Back bonding in \( \text{CCl}_3^{-} \) is from carbon to chlorine but reversed in \( \text{CCl}_2 \).
- **Evaluation**: This is correct. The back bonding direction is indeed different in both cases.

4. **Statement 4**: The direction of back bonding is just opposite in the two cases.
- **Evaluation**: This is also correct. The direction of back bonding is opposite in \( \text{CCl}_3^{-} \) and \( \text{CCl}_2 \).

### Conclusion
- The correct statements are **3 and 4**.