The order of decreasing reactivity towards electrophilic reagent for the following :
(a) Benzene
(b) Toluene
(c ) Chloro benzene
(d) Phenol

Options

A. `b gt d gt a gt c `
B. `d gt c gt b gt a`
C. `d gt b gt a gt c`
D. `a gt b gt c gt d`

Answer

To determine the order of decreasing reactivity towards electrophilic reagents for the compounds benzene, toluene, chlorobenzene, and phenol, we need to analyze how substituents on the benzene ring affect its electron density. The more electron-rich the benzene ring is, the more reactive it will be towards electrophiles.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- (a) Benzene
- (b) Toluene (methyl group attached)
- (c) Chloro benzene (chlorine attached)
- (d) Phenol (hydroxyl group attached)

2. **Understand the Electron Density**:
- Benzene has a stable aromatic system with 6 π electrons, making it a good candidate for electrophilic attack.
- Toluene has a methyl group (-CH₃) which is an electron-donating group (+I effect). This increases the electron density on the benzene ring, making it more reactive than benzene.
- Chlorobenzene has a chlorine atom (-Cl) which has a -I effect (inductive effect) that pulls electron density away from the benzene ring, making it less reactive than benzene.
- Phenol has a hydroxyl group (-OH) which can donate electrons through resonance (+R effect). This significantly increases the electron density on the benzene ring, making it more reactive than both benzene and toluene.

3. **Rank the Reactivity**:
- **Most Reactive**: Phenol (due to +R effect)
- **Next**: Toluene (due to +I effect)
- **Then**: Benzene (neutral)
- **Least Reactive**: Chloro benzene (due to -I effect)

4. **Final Order of Reactivity**:
- The order of decreasing reactivity towards electrophilic reagents is:
- (d) Phenol > (b) Toluene > (a) Benzene > (c) Chloro benzene

### Summary of the Order:
- **Phenol > Toluene > Benzene > Chloro benzene**