Which among the following is deactivating group ?

Options

A. `-Cl`
B. `-OR`
C. `-NH_(2)`
D. `-NHR`

Explanation

To determine which among the given options is a deactivating group, let's analyze each option step by step.

### Step 1: Understanding Deactivating Groups
A deactivating group is a substituent that reduces the reactivity of the benzene ring towards electrophilic substitution reactions. This typically occurs due to the presence of electron-withdrawing effects, such as the -I (inductive) effect or -M (mesomeric) effect.

### Step 2: Analyzing Option A (Cl)
- Chlorine (Cl) exhibits both a -I effect (inductive effect) and a +R effect (resonance effect).
- The -I effect means that chlorine pulls electron density away from the benzene ring, which destabilizes the carbocation intermediate formed during electrophilic substitution.
- Although it has a +R effect due to resonance, the -I effect is stronger in this case.
- **Conclusion**: Cl is a deactivating group.

### Step 3: Analyzing Option B (OR)
- The OR group (alkoxy group) has an oxygen atom that is electronegative.
- The R group (alkyl) can donate electron density through the +I effect.
- Overall, the OR group acts as an electron-donating group due to the +I effect, which enhances the reactivity of the benzene ring.
- **Conclusion**: OR is an activating group.

### Step 4: Analyzing Option C (NH2)
- The NH2 group (amino group) is a strong electron-donating group.
- The nitrogen atom can donate electron density through resonance (+R effect) and has no significant -I effect.
- This makes the benzene ring more reactive towards electrophilic substitution.
- **Conclusion**: NH2 is an activating group.

### Step 5: Analyzing Option D (NHR)
- The NHR group (where R is an alkyl group) also acts as an electron-donating group.
- Similar to NH2, the nitrogen atom can donate electron density through resonance (+R effect).
- Thus, it does not withdraw electrons significantly.
- **Conclusion**: NHR is an activating group.

### Final Conclusion
After analyzing all the options, the only deactivating group among the given options is **Option A: Cl**.