The pairs having only electrophiles are :

Options

A. `BF_3 , CH_(3)^(+)`
B. `RCOO^(-), NH_(3)`
C. `AlCl_(3), SO_(3)`
D. `SO_(3), ROR`

Answer

To determine which pairs contain only electrophiles, we need to identify the electron-deficient species in the given options. An electrophile is defined as an electron-deficient species that seeks to accept electrons to complete its octet. Let's analyze the options step by step.

### Step 1: Understanding Electrophiles
- **Definition**: Electrophiles are species that are electron-deficient and can accept electrons.
- **Characteristics**: They typically have incomplete octets or positive charges.

### Step 2: Analyzing Each Pair
1. **Pair 1: BF3 and CH3+**
- **BF3**: Boron has 3 valence electrons and forms bonds with three fluorine atoms. It has only 6 electrons around it, making it electron-deficient. Thus, BF3 is an electrophile.
- **CH3+**: The carbon in CH3+ has only 6 electrons (3 bonds with hydrogen and a positive charge). This makes it electron-deficient as well. Therefore, CH3+ is also an electrophile.
- **Conclusion**: Both species in this pair are electrophiles.

2. **Pair 2: RCOO- and NH3**
- **RCOO-**: The carbon in the carboxylate ion (RCOO-) has a complete octet (8 electrons) due to resonance stabilization. Thus, it is not an electrophile.
- **NH3**: Ammonia has a complete octet (8 electrons) with nitrogen having a lone pair. Therefore, NH3 is not an electrophile.
- **Conclusion**: Neither species in this pair is an electrophile.

3. **Pair 3: AlCl3 and SO3**
- **AlCl3**: Aluminum has 3 valence electrons and forms bonds with three chlorine atoms. It has only 6 electrons around it, making it electron-deficient. Therefore, AlCl3 is an electrophile.
- **SO3**: Sulfur in SO3 has 6 valence electrons and forms double bonds with three oxygen atoms, completing its octet. However, due to the electronegativity of oxygen, there is a partial positive charge on sulfur, making SO3 act as an electrophile in reactions (e.g., sulfonation).
- **Conclusion**: Both species in this pair are electrophiles.

4. **Pair 4: ROR (ether)**
- **ROR**: In ethers, both carbon and oxygen have complete octets. Thus, ROR does not have any electron-deficient species.
- **Conclusion**: Neither species in this pair is an electrophile.

### Final Answer
The pairs that contain only electrophiles are:
- Pair 1: BF3 and CH3+
- Pair 3: AlCl3 and SO3

### Summary
The correct pairs having only electrophiles are **Pair 1 (BF3 and CH3+)** and **Pair 3 (AlCl3 and SO3)**.