Arrange in decreasing order of + R power in the given groups
(1) `-NH_2`
(2) `-O^(Theta)`
(3) `-OH`
(4) `-NHCOCH_3`

Options

A. `2gt1gt3gt4`
B. `2gt3gt1gt4`
C. `1gt2gt3gt4`
D. `3gt2gt1gt4`

Answer

To arrange the given substituents in decreasing order of their +R (positive resonance) power, we need to analyze each substituent's ability to donate electron density through resonance. Let's break down the process step by step:

### Step 1: Identify the substituents
The substituents given are:
1. `-NH2` (Amino group)
2. `-O^(-)` (Negative oxygen, typically considered as an alkoxide)
3. `-OH` (Hydroxyl group)
4. `-NHCOCH3` (Acetamido group)

### Step 2: Understand the +R effect
The +R effect refers to the ability of a substituent to donate electron density to an aromatic ring through resonance. Groups that have lone pairs of electrons can participate in resonance and thus exhibit +R effect.

### Step 3: Analyze each substituent
1. **`-NH2` (Amino group)**: The nitrogen has a lone pair that can be donated to the aromatic ring, thus exhibiting a strong +R effect.

2. **`-O^(-)` (Negative oxygen)**: This group has a negative charge and can donate electron density very effectively. It has a strong +R effect due to the presence of the negative charge.

3. **`-OH` (Hydroxyl group)**: The oxygen in the hydroxyl group has a lone pair that can participate in resonance, but it is less effective than the amino group because it is less basic and has a stronger electronegativity.

4. **`-NHCOCH3` (Acetamido group)**: The nitrogen has a lone pair, but it is involved in resonance with the carbonyl (C=O) of the acetamido group, which withdraws electron density. Therefore, it exhibits a weaker +R effect compared to the amino and hydroxyl groups.

### Step 4: Compare the +R effects
Now, we can rank these substituents based on their ability to donate electron density:
- **Highest +R effect**: `-O^(-)` (Negative oxygen)
- **Second highest +R effect**: `-NH2` (Amino group)
- **Third highest +R effect**: `-OH` (Hydroxyl group)
- **Lowest +R effect**: `-NHCOCH3` (Acetamido group)

### Final Order
Thus, the final order in decreasing order of +R power is:
1. `-O^(-)`
2. `-NH2`
3. `-OH`
4. `-NHCOCH3`