Arrange reactivity of given compounds in decreasing order for electrophilic substitution reaction
1. Furan
2. Pyrrole
3. Thiophene

Options

A. 1,2,3
B. 2,1,3
C. 2,3,1
D. 3,2,1

Answer

To arrange the reactivity of the given compounds (Furan, Pyrrole, and Thiophene) in decreasing order for electrophilic substitution reactions, we will analyze the structures and the factors affecting their reactivity.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Furan (C4H4O)
- Pyrrole (C4H4N)
- Thiophene (C4H4S)

2. **Understand Electrophilic Substitution**:
- Electrophilic substitution reactions involve the attack of an electrophile on the π-electron cloud of the compound. The reactivity depends on the electron density available on the ring.

3. **Analyze Electron Density**:
- **Pyrrole**: Contains a nitrogen atom which has a lone pair that can contribute to the π-system, increasing the electron density. Nitrogen is less electronegative than oxygen, allowing it to donate electron density effectively.
- **Furan**: Contains an oxygen atom which is more electronegative than nitrogen. The lone pair on oxygen is involved in resonance but is less effective in increasing electron density on the ring due to its electronegativity.
- **Thiophene**: Contains sulfur, which is less electronegative than oxygen but has a 3p orbital that does not overlap as effectively with the 2p orbitals of carbon, resulting in less effective electron donation to the π-system compared to nitrogen in pyrrole.

4. **Compare Reactivity**:
- **Pyrrole** is the most reactive due to the effective donation of electron density from nitrogen.
- **Furan** is next, as oxygen's electronegativity reduces its ability to enhance electron density compared to nitrogen.
- **Thiophene** is the least reactive due to poor orbital overlap and less effective electron donation from sulfur.

5. **Final Arrangement**:
- The decreasing order of reactivity for electrophilic substitution reactions is:
1. Pyrrole (most reactive)
2. Furan
3. Thiophene (least reactive)

### Final Answer:
The decreasing order of reactivity for electrophilic substitution reaction is:
**Pyrrole > Furan > Thiophene**