Here’s a explanation of the role of molecular orbitals (MOs) in chemical reactivity:
1. Molecular Orbitals and Electrons
- Molecular orbitals are regions where electrons are most likely to be found in a molecule.
- Electrons in these orbitals determine how a molecule can interact with others.
2. HOMO and LUMO
Two orbitals are especially important for reactivity:
- HOMO (Highest Occupied Molecular Orbital)
- Contains the most reactive electrons in a molecule.
- Acts as an electron donor in reactions.
- LUMO (Lowest Unoccupied Molecular Orbital)
- The lowest energy orbital that is empty.
- Can accept electrons from another molecule.
Key idea:
- Chemical reactions often occur when electrons move from the HOMO of one molecule to the LUMO of another.
3. Predicting Reactivity
- MO theory helps explain:
- Why some molecules are more reactive than others.
- The sites in a molecule where reactions are likely to happen.
- Stability of molecules (delocalized MOs → more stable).
Example:
- In ethene (C₂H₄), the π bond electrons (in HOMO) can react with electrophiles (species that accept electrons) because the π electrons are easily accessible.
4. Summary
- MOs show where electrons are.
- HOMO → donor, LUMO → acceptor.
- Reactivity is controlled by how electrons in MOs interact with other molecules.