Lecture on Hybridization in Organic Chemistry

Key Concepts

• Hybridization: Process of mixing atomic orbitals to form new hybrid orbitals suitable for pairing electrons
• SP3 Hybridization: Occurs when carbon is bonded to four atoms, resulting in a tetrahedral geometry with bond angles of 109.5 degrees

SP2 Hybridization

• Example: Ethylene molecule (C2H4)
• Geometry: Planar with bond angles of approximately 120 degrees
• Carbon Bonding:
  • Each carbon is bonded to three atoms (two hydrogens and one carbon)
  • Different hybridization needed from SP3

Electron Configuration and Hybridization

• Starting Point: Carbon's excited state with four valence electrons
• SP2 Formation:
  • Promote the S orbital
  • Combine one S orbital and two P orbitals
  • Leaves one P orbital unhybridized

SP2 Orbital Characteristics

• SP2 Hybrid Orbitals:
  • Formed from 1 S orbital and 2 P orbitals
  • Comprise of 33% S character and 67% P character
• Impact:
  • Increased S character results in electron density closer to the nucleus, leading to shorter bond lengths

Ethylene Molecule Structure

• Hybrid Orbital Arrangement:
  • Each carbon has three SP2 orbitals and one unhybridized P orbital
• Bonding:
  • Sigma bonds: Formed by head-on overlap (5 in ethylene)
  • Pi bonds: Formed by side-by-side overlap of unhybridized P orbitals

Bond Characteristics

• Double Bond: Composed of one sigma and one pi bond
• Bond Length: Shorter in ethylene (1.34 Å) compared to ethane (1.54 Å) due to increased S character

Steric Number and Hybridization

• Definition: Sum of sigma bonds and lone pairs
• Application: Helps determine hybridization (e.g., steric number of 3 implies SP2 hybridization)

Boron Trifluoride (BF3) Example

• Structure:
  • Boron bonded to three fluorines
  • Planar geometry with 120-degree bond angles
• Hybridization: Boron is SP2 hybridized
• Chemical Behavior:
  • Boron can accept an electron pair in its empty P orbital, acting as a Lewis acid

Conclusion

• The concepts of hybridization are fundamental in understanding the geometry and reactivity of organic molecules.
• In the next topic, SP hybridization will be explored.