Chapter 5 Lecture: Frontier Molecular Orbital Theory

Announcements

• Grading for individual exams nearly complete.
• Exams results expected by end of the day tomorrow or by noon on Wednesday.
• Group exams grading to follow.
• Ensure familiarity with Panopto for accessing course videos.

Lecture Overview

• Focus on understanding chemical reactivity through molecular orbitals.
• Importance of creating new molecules for applications such as drugs and pesticides.
• Introduction to molecular orbitals: understanding interactions at the molecular level.

Review of Molecular Orbital Theory

• Molecular orbital diagrams explain electron locations in molecules.
• Example: F2 molecule
  • Electron configuration for fluorine: [He] 2s² 2p⁵.
  • Combining atomic orbitals to form molecular orbitals.
  • Bonding and antibonding orbitals.

Frontier Molecular Orbitals

• HOMO (Highest Occupied Molecular Orbital)
  • Most reactive electrons.
• LUMO (Lowest Unoccupied Molecular Orbital)
  • Electrons added here will find the most attraction.
• Reactivity is primarily determined by HOMO and LUMO interactions.

Chemical Reaction Types

1. Bond Making: Sharing electron pairs between molecules.
2. Bond Breaking: Redistribution of electron pairs.
3. Substitution Reaction: Simultaneous bond making and breaking.

Reaction Mechanisms

• Use arrows to depict movement of electrons.
• Electrons dictate reactivity, not atoms.

Practical Examples

1. F2 + N2 Reaction
   • Use molecular orbital theory to predict electron donor and acceptor.
   • HOMO of N2 and LUMO of F2 interact.
   • Predict reaction products using molecular orbital diagrams.
2. Formaldehyde and Water Reaction
   • Determine electron donor and acceptor based on HOMO and LUMO energies.
   • Use frontier molecular orbital theory to anticipate product formation.

Key Concepts

• Molecular orbitals help predict the reactivity and formation of new compounds.
• Reactivity largely governed by electron distribution in frontier orbitals.
• Understanding orbital interactions essential for predicting chemical behavior.

Conclusion

• Application of frontier molecular orbital theory in predicting chemical reactions.
• Emphasis on using molecular orbital diagrams in understanding chemical properties.
• Preparation for organic chemistry through foundational understanding of reactivity.

---

• Next session: Further exploration of similar reactions in lab sessions.