Which of the following species shows intramolecular hydrogen bonding ? (A)o-Nitrophenol (B)p- Nitrophenol (C)Benzoic acid (D) Ethanol

Options

A. o-Nitrophenol
B. p- Nitrophenol
C. Benzoic acid
D. Ethanol

Explanation

To determine which of the given species shows intramolecular hydrogen bonding, we will analyze each option step by step.

### Step 1: Understand Intramolecular Hydrogen Bonding
Intramolecular hydrogen bonding occurs when a hydrogen bond forms within the same molecule, involving a hydrogen atom bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom in the same molecule.

### Step 2: Analyze Each Option

#### Option A: o-Nitrophenol
- **Structure**: o-Nitrophenol has a hydroxyl group (-OH) and a nitro group (-NO2) attached to the benzene ring at the ortho position (adjacent to each other).
- **Hydrogen Bonding**: The hydrogen atom of the hydroxyl group can form a hydrogen bond with the oxygen atom of the nitro group, creating a five-membered ring structure within the same molecule.
- **Conclusion**: This species exhibits intramolecular hydrogen bonding.

#### Option B: p-Nitrophenol
- **Structure**: p-Nitrophenol has the hydroxyl group and the nitro group attached to the benzene ring at the para position (opposite sides).
- **Hydrogen Bonding**: In this case, the hydroxyl group cannot form a hydrogen bond with the nitro group within the same molecule due to their separation.
- **Conclusion**: This species does not exhibit intramolecular hydrogen bonding; instead, it can form intermolecular hydrogen bonds with other p-nitrophenol molecules.

#### Option C: Benzoic Acid
- **Structure**: Benzoic acid has a carboxyl group (-COOH) attached to the benzene ring.
- **Hydrogen Bonding**: The carboxyl group can form hydrogen bonds with other benzoic acid molecules, but not within the same molecule.
- **Conclusion**: This species does not exhibit intramolecular hydrogen bonding; it primarily shows intermolecular hydrogen bonding.

#### Option D: Ethanol
- **Structure**: Ethanol has a hydroxyl group (-OH) attached to an ethyl group (C2H5).
- **Hydrogen Bonding**: Ethanol can form hydrogen bonds with other ethanol molecules, but there is no potential for intramolecular hydrogen bonding as the hydroxyl group is not close enough to another electronegative atom within the same molecule.
- **Conclusion**: This species does not exhibit intramolecular hydrogen bonding; it shows intermolecular hydrogen bonding.

### Final Conclusion
Based on the analysis, the only species that shows intramolecular hydrogen bonding is **(A) o-Nitrophenol**.