In which of the following cases `C-C` bond length will be highest?

Options

A. `CH_(3)-CF_(3)`
B. `FCH_(2)-CH_(2)F`
C. `F_(2)CH-CHF_(2)`
D. `CF_(3)-CF_(3)`

Explanation

To determine which of the given compounds has the highest C-C bond length, we need to analyze the influence of electronegative substituents on the bond length. Let's go through the steps to arrive at the solution.

### Step-by-Step Solution:

1. **Understand the Concept of Bond Length**:
The bond length between two atoms is influenced by the type of bond (single, double, triple) and the electronegativity of the substituents attached to the atoms involved in the bond. Generally, the more electronegative the substituents, the shorter the bond length due to increased s-character in the hybridization.

2. **List the Compounds**:
The compounds given in the question are:
- CH3-CF3
- FCH2-CH2F
- F2-CH
- CHF2
- CF3-CF3

3. **Analyze Each Compound**:
- **CH3-CF3**: Contains one electronegative fluorine substituent.
- **FCH2-CH2F**: Contains two fluorine substituents, which increases the electronegativity effect.
- **F2-CH**: Contains two fluorine substituents but is a terminal carbon.
- **CHF2**: Contains one fluorine substituent.
- **CF3-CF3**: Contains three fluorine substituents on both carbons.

4. **Apply the Concept of p-Character**:
According to Ben's rule, the more electronegative substituents attached to hybrid orbitals that contain more p-character will lead to longer bond lengths. This is because increased p-character leads to weaker bonds.

5. **Identify the Compound with Highest Bond Length**:
- Among the compounds, **FCH2-CH2F** has the highest number of electronegative substituents (two fluorine atoms), which will lead to a significant increase in p-character and thus a longer C-C bond length.

6. **Conclusion**:
Therefore, the compound with the highest C-C bond length is **FCH2-CH2F**.

### Final Answer:
The C-C bond length will be highest in **FCH2-CH2F**.