Overview
This lecture covers the rotation properties of single, double, and triple carbon bonds, hybridization types (sp3, sp2, sp), bond angles, and how carbon’s small size enables diverse and stable bonding.
Bond Rotation and Structure
- Single (sigma) bonds in carbon allow free rotation, leading to many structural arrangements.
- Double bonds (sigma + pi) have restricted rotation, causing geometric isomerism (cis/trans forms).
- Triple bonds (one sigma, two pi) do not allow rotation, maintaining a linear shape.
Hybridization Types and Bond Angles
- sp3 hybridization: carbon has four electron groups, forms tetrahedral geometry, bond angle ~109.5°.
- sp2 hybridization: carbon has three electron groups, forms trigonal planar geometry, bond angle ~120°.
- sp hybridization: carbon has two electron groups, forms linear geometry, bond angle 180°.
Geometric Isomerism
- Double bonds can yield cis isomers (groups on same side) and trans isomers (groups on opposite sides).
- Geometric isomers have the same molecular formula but different spatial arrangement due to restricted rotation.
Structural Representation and Examples
- Skeletal structures represent organic molecules without showing hydrogens.
- Rotating around single bonds can give different arrangements, but double bonds limit rotation and create distinct isomers.
Special Properties of Carbon Bonds
- Carbon’s small atomic size allows strong sigma bond overlap for stable bonds.
- Short carbon–carbon bonds enable formation of sigma and pi bonds, increasing structural variety.
- Carbon’s ability to catenate (form chains, branches, rings) underlies organic molecule diversity.
Key Terms & Definitions
- Hybridization — Mixing of atomic orbitals to form new orbitals for bonding.
- Sigma bond — Single covalent bond formed by end-to-end overlap.
- Pi bond — Covalent bond formed by side-to-side overlap above and below the bond axis.
- Geometric isomerism — Existence of molecular isomers with different spatial arrangements due to restricted bond rotation.
- Catenation — Ability of an element to form long chains or rings with itself.
Action Items / Next Steps
- Create flashcards for carbon hybridization types, bond angles, and examples of isomers.
- Review skeletal structure representations and practice identifying isomers.
- Prepare for discussion on carbon catenation (chains, branches, rings) in the next session.