Which of the following reactions are used for detecting presence of carbonyl group?

Options

A. Reaction with hydroxylamine
B. Reaction with hydrazine
C. Reaction with phenylhydrazine
D. Reaction with semicarbazide

Answer

To determine which reactions can be used to detect the presence of a carbonyl group, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Carbonyl Groups**:
- Carbonyl groups (C=O) are present in aldehydes and ketones. Detecting them is crucial in organic chemistry.

2. **Option 1: Reaction with Hydroxylamine**:
- Hydroxylamine (NH2OH) reacts with carbonyl compounds to form oximes.
- The reaction can be represented as:
\[ RCHO + NH_2OH \rightarrow RCH=NOH + H_2O \]
- This indicates that hydroxylamine can indeed be used to detect carbonyl groups.

3. **Option 2: Reaction with Hydrogen**:
- The term "reaction with hydrogen" is ambiguous. If it refers to hydrogenation (adding hydrogen to the carbonyl), it does not specifically indicate detection of the carbonyl group.
- Therefore, this option is not typically used for detection.

4. **Option 3: Reaction with Phenylhydrazine**:
- Phenylhydrazine (C6H5NHNH2) reacts with carbonyl compounds to form hydrazones.
- The reaction can be represented as:
\[ RCHO + C_6H_5NHNH_2 \rightarrow RCH=N-NHC_6H_5 + H_2O \]
- This indicates that phenylhydrazine can also be used to detect carbonyl groups.

5. **Option 4: Reaction with Semicarbazide**:
- Semicarbazide (NH2NHCONH2) reacts with carbonyl compounds to form semicarbazones.
- The reaction can be represented as:
\[ RCHO + NH_2NHCONH_2 \rightarrow RCH=N-NHCONH_2 + H_2O \]
- This indicates that semicarbazide can be used for the detection of carbonyl groups.

### Conclusion:
- The reactions that can be used for detecting the presence of carbonyl groups are:
- Reaction with Hydroxylamine
- Reaction with Phenylhydrazine
- Reaction with Semicarbazide

Thus, the correct answers are:
- Hydroxylamine
- Phenylhydrazine
- Semicarbazide