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 (denoted as +M effect), we will analyze each option step by step.

### Step 1: Understand the Concept of Mesomeric Effect
The mesomeric effect refers to the delocalization of electrons through pi bonds or lone pairs in a molecule, which can either donate or withdraw electron density. The +M effect indicates that a group donates electron density through resonance.

**Hint:** Remember that groups with lone pairs or double bonds adjacent to a positively charged atom typically exhibit a +M effect.

### Step 2: Analyze Option 1
In the first option, we have a nitrogen with a positive charge adjacent to a carbonyl (C=O) group. The positive charge on nitrogen indicates that it is electron-deficient. Therefore, it will not effectively donate electron density.

**Hint:** A positive charge on an atom reduces its ability to donate electrons.

### Step 3: Analyze Option 2
In the second option, nitrogen is bonded to two methyl groups. Methyl groups exhibit a +I (inductive) effect, which increases the electron density on nitrogen. This increased electron density allows nitrogen to effectively donate electrons through resonance.

**Hint:** Look for groups that increase electron density on the donating atom; methyl groups can help in this case.

### Step 4: Analyze Option 3
In the third option, nitrogen is bonded to a carbonyl (C=O) group and has a hydrogen atom. The carbonyl group is an electron-withdrawing group (-I effect), which decreases the electron density on nitrogen. Therefore, nitrogen cannot effectively donate electrons.

**Hint:** Electron-withdrawing groups reduce the electron density on adjacent atoms, limiting their ability to donate electrons.

### Step 5: Analyze Option 4
In the fourth option, we have an oxygen atom with two lone pairs adjacent to a carbonyl group. The electronegativity of oxygen means that it will not effectively donate its lone pairs due to the presence of the electron-withdrawing carbonyl group.

**Hint:** Electronegativity plays a crucial role; highly electronegative atoms will tend to hold onto their electrons rather than donate them.

### Conclusion
After analyzing all options, we find that **Option 2** has the strongest electron donating mesomeric effect due to the presence of methyl groups enhancing the electron density on nitrogen.

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