How many of the following substituents can cause aromatic electrophilic substitution faster than benzene ?
(a)`-NH_2` , (b)`-NR_2` , ( C)`-NO_2` , (d)`-overset(+)NH_3`
(e)`-O-oversetoverset(O)(||)C-R` , (f) `-NH-oversetoverset(O)(||)C-R` , (g)`-oversetoverset(O)(||)C-Cl` , (h)`-oversetoverset(O)(||)C-H`
(i)`-SO_3H` , (j)`-CH_3` , (k)`-CH-CR_2`

Answer

To determine how many of the given substituents can cause aromatic electrophilic substitution faster than benzene, we need to identify which of these substituents are electron-donating groups. Electron-donating groups increase the electron density on the aromatic ring, making it more reactive towards electrophiles.

Let's analyze each substituent:

1. **(a) -NH2 (Amino group)**:
- The amino group is an electron-donating group due to its ability to donate electrons through resonance (mesomeric effect).
- **Effect**: Increases the reactivity of the aromatic ring.

2. **(b) -NR2 (Dialkylamino group)**:
- Similar to the amino group, the dialkylamino group also donates electrons through resonance.
- **Effect**: Increases the reactivity of the aromatic ring.

3. **(c) -NO2 (Nitro group)**:
- The nitro group is a strong electron-withdrawing group due to resonance and inductive effects.
- **Effect**: Decreases the reactivity of the aromatic ring.

4. **(d) -NH3+ (Ammonium ion)**:
- The ammonium ion has a positive charge, which attracts electrons from the aromatic ring, thus decreasing its electron density.
- **Effect**: Decreases the reactivity of the aromatic ring.

5. **(e) -O(C=O)R (Ester group)**:
- The ester group is electron-withdrawing due to resonance and inductive effects.
- **Effect**: Decreases the reactivity of the aromatic ring.

6. **(f) -NH(C=O)R (Amide group)**:
- The amide group is also electron-withdrawing due to resonance and inductive effects.
- **Effect**: Decreases the reactivity of the aromatic ring.

7. **(g) -C(=O)Cl (Acyl chloride)**:
- The acyl chloride is electron-withdrawing due to resonance and inductive effects.
- **Effect**: Decreases the reactivity of the aromatic ring.

8. **(h) -C(=O)H (Aldehyde)**:
- The aldehyde group is electron-withdrawing due to resonance and inductive effects.
- **Effect**: Decreases the reactivity of the aromatic ring.

9. **(i) -SO3H (Sulfonic acid)**:
- The sulfonic acid group is electron-withdrawing.
- **Effect**: Decreases the reactivity of the aromatic ring.

10. **(j) -CH3 (Methyl group)**:
- The methyl group is a weak electron-donating group due to inductive effects.
- **Effect**: Increases the reactivity of the aromatic ring.

11. **(k) -C(CH3)2 (Alkyl group)**:
- Similar to the methyl group, this alkyl group increases electron density through inductive effects.
- **Effect**: Increases the reactivity of the aromatic ring.

Now, let's summarize the findings:

- **Electron-donating groups**:
- (a) -NH2
- (b) -NR2
- (j) -CH3
- (k) -C(CH3)2

- **Electron-withdrawing groups**:
- (c) -NO2
- (d) -NH3+
- (e) -O(C=O)R
- (f) -NH(C=O)R
- (g) -C(=O)Cl
- (h) -C(=O)H
- (i) -SO3H

**Total number of substituents that can cause aromatic electrophilic substitution faster than benzene**: 4