Arrange the carbanions, `(CH_(3))_(3)bar(C),bar(C)Cl_(3),(CH_(3))_(2)bar(C)H,C_(6)H_(5)bar(C)H_(2)`, in order of their decreasing stability

Explanation

To arrange the carbanions `(CH₃)₃C⁻`, `CCl₃⁻`, `(CH₃)₂CH⁻`, and `C₆H₅CH₂⁻` in order of their decreasing stability, we will analyze each carbanion based on the effects of substituents and resonance stabilization.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **A**: `(CH₃)₃C⁻` (tert-butyl carbanion)
- **B**: `CCl₃⁻` (trichloromethyl carbanion)
- **C**: `(CH₃)₂CH⁻` (isopropyl carbanion)
- **D**: `C₆H₅CH₂⁻` (benzyl carbanion)

2. **Analyze Stability Factors**:
- Carbanion stability is influenced by the ability of substituents to stabilize the negative charge through inductive effects (−I) and resonance effects (−R).

3. **Evaluate Each Carbanion**:
- **A: `(CH₃)₃C⁻`**: The three methyl groups are electron-donating (through +I effect), which increases electron density on the carbanion, making it unstable. Thus, it is the least stable.
- **B: `CCl₃⁻`**: The three chlorine atoms are highly electronegative and exhibit a strong −I effect, pulling electron density away from the carbanion, stabilizing it. This makes it more stable than A.
- **C: `(CH₃)₂CH⁻`**: This carbanion has two methyl groups that provide some +I effect, but it is less destabilizing than in A due to having only two electron-donating groups. It is more stable than A but less stable than B.
- **D: `C₆H₅CH₂⁻`**: The negative charge on the benzylic position can be stabilized by resonance with the benzene ring, making this carbanion the most stable of all.

4. **Order of Stability**:
- Based on the analysis:
- D (benzyl carbanion) is the most stable due to resonance.
- B (trichloromethyl carbanion) is next due to strong −I effect from chlorine.
- C (isopropyl carbanion) follows due to moderate +I effect.
- A (tert-butyl carbanion) is the least stable due to excessive +I effect.

5. **Final Arrangement**:
- The order of decreasing stability is: **D > B > C > A**.

### Summary:
The final order of decreasing stability for the carbanions is:
**C₆H₅CH₂⁻ > CCl₃⁻ > (CH₃)₂CH⁻ > (CH₃)₃C⁻**