Dr E. Ramanathan PhD
Level: STD 11/12, Chemistry, NEET, JEE aspirants
Hydrogen bonding is a type of dipole-dipole interaction that occurs when a hydrogen atom, covalently bonded to a highly electronegative atom (such as fluorine (F), oxygen (O), or nitrogen (N)), interacts with a lone pair of electrons on another electronegative atom.
Key Features:
- Requires:
- A hydrogen atom attached to F, O, or N (donor).
- A lone pair on F, O, or N (acceptor).
- Nature:
- Weaker than covalent bonds, but stronger than van der Waals forces.
- Partial electrostatic attraction + some covalent character.
Types:
- Intermolecular Hydrogen Bonding – between molecules (e.g., water, HF).
- Intramolecular Hydrogen Bonding – within the same molecule (e.g., o-nitrophenol).
Effects:
- Raises boiling and melting points.
- Increases solubility in water.
- Influences molecular structure and biological function (e.g., DNA base pairing, protein folding).
Intermolecular vs Intramolecular Hydrogen Bonding:
| Feature | Intermolecular Hydrogen Bonding | Intramolecular Hydrogen Bonding |
|---|---|---|
| Definition | Hydrogen bond between different molecules | Hydrogen bond within the same molecule |
| Effect | Increases boiling/melting point, viscosity, solubility | May decrease solubility, alters molecule geometry |
| Example | Water (H₂O), alcohols like ethanol (CH₃CH₂OH) | Ortho-nitrophenol, salicylaldehyde |
| Occurrence | Common in polar solvents | Occurs when donor and acceptor groups are close in a molecule |
| Strength | Generally stronger due to full molecule interaction | Often weaker, limited by molecular strain |
| Impact on state | Helps in forming liquids or networks like ice | Affects conformation or reactivity of molecule |
Summary:
- Intermolecular = between molecules
- Intramolecular = within one molecule
