Arrange in order of decresing trend towards `S_(E)` reactions,
`{:("Chlorobenzen","Benzene","Anilinium chloride","Toluene"),(I,II,III,IV):}`

Options

A. `IgtIgtIIIgtIV`
B. `IIIgtIgtIIgtIV`
C. `IVgtIIgtIgtIII`
D. `IgtIIgtIIIgtIV`

Answer

To arrange the compounds in order of decreasing trend towards electrophilic substitution (SE) reactions, we need to analyze the nature of the substituents on the benzene ring for each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- I: Chlorobenzene
- II: Benzene
- III: Anilinium chloride
- IV: Toluene

2. **Understand Electrophilic Substitution (SE)**:
- Electrophilic substitution reactions occur when an electrophile attacks the aromatic ring and substitutes one of the hydrogen atoms.
- The reactivity towards SE is influenced by the nature of the substituent on the benzene ring:
- **Electron-donating groups** (EDGs) increase the electron density on the ring, making it more reactive towards electrophiles.
- **Electron-withdrawing groups** (EWGs) decrease the electron density, making the ring less reactive.

3. **Analyze Each Compound**:
- **Chlorobenzene (I)**: Chlorine is an electron-withdrawing group due to its -I effect (inductive effect) but has a +M effect (mesomeric effect). However, the -I effect is stronger, making chlorobenzene a deactivator for SE reactions.
- **Benzene (II)**: Benzene has no substituents, so it is neutral in terms of reactivity. It has a moderate reactivity towards SE.
- **Anilinium Chloride (III)**: Anilinium chloride has a positively charged nitrogen (NH3+), which strongly withdraws electrons from the ring, making it a very poor candidate for SE reactions.
- **Toluene (IV)**: Toluene has a methyl group (-CH3), which is an electron-donating group due to hyperconjugation and +I effect. This increases the reactivity towards SE.

4. **Order of Reactivity**:
- **Most Reactive**: Toluene (IV) - due to the electron-donating methyl group.
- **Next**: Benzene (II) - neutral, moderate reactivity.
- **Third**: Chlorobenzene (I) - electron-withdrawing chlorine reduces reactivity.
- **Least Reactive**: Anilinium chloride (III) - strong electron-withdrawing effect due to the positively charged nitrogen.

5. **Final Arrangement**:
The order of decreasing trend towards SE reactions is:
- IV: Toluene > II: Benzene > I: Chlorobenzene > III: Anilinium chloride

### Answer:
The order of decreasing trend towards SE reactions is:
**Toluene > Benzene > Chlorobenzene > Anilinium Chloride** (IV > II > I > III)

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