In which of the following reactions, the intermediate species acyl nitrene `(R-overset(O)overset(||)(C)-ddot(N: ))` and intermediate compound alkyl isocyanate `(R - N = C = O)` are involved ?

Options

A.
B.
C.
D.

Explanation

To determine which reactions involve the intermediate species acyl nitrene `(R-C(=O)-N:)` and the intermediate compound alkyl isocyanate `(R-N=C=O)`, we will analyze each of the provided reactions step-by-step.

### Step 1: Analyze Reaction A - Hoffman Degradation
1. **Starting Material**: The reaction begins with an amide `R-C(=O)-NH2`.
2. **Base Attack**: The hydroxide ion (OH-) attacks the hydrogen on the nitrogen, leading to the formation of a negatively charged intermediate.
3. **Bromination**: The negatively charged nitrogen attacks bromine (Br2), forming an intermediate that contains the isocyanate group `R-N=C=O`.
4. **Final Product**: The reaction proceeds to form `R-NH2` and releases carbon dioxide (CO2).
5. **Conclusion**: In this reaction, the intermediate `R-N=C=O` is formed.

### Step 2: Analyze Reaction B - Laws and Rearrangement
1. **Starting Material**: The reaction starts with a hydroxylamine derivative `R3C-NH-OH`.
2. **Formation of Isocyanate**: In the presence of a base, the intermediate `R-N=C=O` is formed.
3. **Nucleophilic Attack**: The isocyanate reacts with methanol (MeOH) to form another intermediate.
4. **Final Product**: This leads to the formation of a substituted urea.
5. **Conclusion**: The intermediate `R-N=C=O` is involved in this reaction.

### Step 3: Analyze Reaction C - Curtius Rearrangement
1. **Starting Material**: The reaction begins with an acyl azide `R-C(=O)-N3`.
2. **Rearrangement**: The azide undergoes rearrangement, resulting in the formation of `R-N=C=O` and nitrogen gas (N2) is released.
3. **Hydrolysis**: When water is added and heated, the isocyanate can hydrolyze to form `R-NH2` and CO2.
4. **Conclusion**: The intermediate `R-N=C=O` is formed in this reaction.

### Step 4: Analyze Reaction D - Schmidt Rearrangement
1. **Starting Material**: The reaction starts with an aldehyde `R-C(=O)H`.
2. **Formation of Intermediate**: The aldehyde reacts with hydrazoic acid (HN3) to form an intermediate that rearranges to yield `R-N=C=O`.
3. **Hydrolysis**: On heating with water, the isocyanate can hydrolyze to form `R-NH2` and CO2.
4. **Conclusion**: The intermediate `R-N=C=O` is also formed in this reaction.

### Final Conclusion
All four reactions (A, B, C, and D) involve the intermediate alkyl isocyanate `(R-N=C=O)`. Therefore, the answer is that all reactions involve the specified intermediates.