Which of the following group will have strongest electron donating mesomeric effect?

Options

A.
B.
C.
D.

Answer

To determine which group has the strongest electron donating mesomeric effect, we will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding Mesomeric Effect**:
- The mesomeric effect (or resonance effect) refers to the delocalization of electrons in a molecule through pi bonds or lone pairs. It occurs when electron density is transferred from a substituent to a conjugated system.

2. **Analyzing Each Option**:
- **Option 1**: This group has a positive charge on nitrogen. A positive charge indicates a deficiency of electrons, meaning it cannot donate electrons effectively. Therefore, the mesomeric effect here is weak or negligible.

- **Option 2**: This group contains two methyl groups. Methyl groups are electron-donating through the +I (inductive) effect. Although they primarily exhibit inductive effects, they can also contribute to the mesomeric effect by increasing electron density on the adjacent atom (like nitrogen). The presence of two methyl groups means that the electron density is increased significantly, making this group a strong electron donor.

- **Option 3**: This group has a carbonyl (C=O) functional group. The carbonyl group is known to have a -I (inductive) effect, meaning it withdraws electron density from adjacent atoms. Therefore, it does not contribute positively to the mesomeric effect and actually decreases electron density.

- **Option 4**: This option is not specified in the transcript, but if it were to contain a strong electron-donating group (like -OH or -OCH3), it could potentially have a strong mesomeric effect. However, based on the analysis of the first three options, we can conclude that option 2 is the strongest.

3. **Conclusion**:
- After analyzing all the options, it is clear that **Option 2**, which contains two methyl groups, exhibits the strongest electron donating mesomeric effect due to the increase in electron density from both groups.

### Final Answer:
**Option 2 has the strongest electron donating mesomeric effect.**