Which of the following group shows `+I-` effect :

Options

A. `-Br`
B. `-COOH`
C. `-OR`
D. `-COO^(-)`

Answer

To determine which of the given groups shows a +I (positive inductive) effect, we need to understand the concept of inductive effects in organic chemistry. The inductive effect refers to the polarization of sigma bonds within a molecule due to the electronegativity differences between atoms.

### Step-by-Step Solution:

1. **Understanding Inductive Effects**:
- The inductive effect can be classified into two types: +I effect (electron-donating) and -I effect (electron-withdrawing).
- +I effect occurs when a group donates electron density towards the rest of the molecule, while -I effect occurs when a group withdraws electron density.

2. **Identifying Groups**:
- We need to analyze the given groups to see whether they exhibit +I or -I effects.

3. **Analyzing Each Group**:
- **Group 1: Bromine (Br)**:
- Bromine is an electronegative atom and tends to pull electron density towards itself.
- Therefore, it shows a -I effect, not +I.

- **Group 2: C=O (Carbonyl group)**:
- The carbonyl group (C=O) has oxygen, which is electronegative.
- It pulls electron density from the carbon, making the carbon electron-deficient.
- Thus, it also shows a -I effect.

- **Group 3: OR (Alkoxy group)**:
- The alkoxy group (R-O) has oxygen, which is again electronegative.
- It pulls electron density towards itself, resulting in a -I effect.

- **Group 4: C=O O- (Carboxylate ion)**:
- In the carboxylate ion (C=O O-), the oxygen with a negative charge can donate electron density.
- The presence of the negative charge indicates that it can provide electrons to the carbon, which can stabilize the positive charge created by the electron withdrawal from the carbonyl.
- Therefore, this group shows a +I effect.

4. **Conclusion**:
- Among the given groups, only the carboxylate ion (C=O O-) exhibits a +I effect, while the others show -I effects.

### Final Answer:
The group that shows a +I effect is **C=O O- (Carboxylate ion)**.