Lecture Notes: Simplifying Organic Molecule Structures

Introduction to Skeletal Structures

• Purpose: Simplify drawing organic molecules by not showing every carbon, hydrogen, and bond.
• Components: Organic molecules contain carbon, hydrogen, and may include oxygen, nitrogen, sulfur, and phosphorus.

Why Carbon is Central in Organic Molecules

• Carbon's Hybridization: Typically sp3 hybridized with 4 valence electrons, forming up to 4 different bonds.
• Complexity and Life: Ability to form large, complex structures which are fundamental to life.

Representations of Organic Molecules

• Condensed Structural Formula: Shows groups like CH₃, CH₂.
• Lewis Structure: Indicates how atoms are bound in detail.
• Skeletal Structures: Efficiently represent molecules without showing all atoms and bonds.

Drawing Skeletal Structures

• Simplicity: Show only bonds between carbon atoms; omit hydrogen bonded to carbon.
• Visible Atoms: Only non-carbon and hydrogen atoms like O, N, S, and P are shown.

Example: Butane (C₄H₁₀)

• Structure: 4 carbon atoms, 3 bonds between them.
• Counting Carbons: Every corner or bend indicates a carbon atom.
• Hydrogen Counting: Calculate hidden hydrogens by subtracting visible bonds from 4.

Example: Pentane

• Counting Carbons: Ensure correct number by numbering from the start.
• Hydrogens: Generally ignored unless necessary.

Consideration of Different Spatial Configurations

• Hybridization and Bond Angles: sp3 carbons have ~109.5° angles, typically represented as ~120° for simplicity.
• Visualization: Highlight technique to ensure correct structure understanding.

Complex Structures

• Cyclohexane: Draw as a ring; number to verify.
• Chair Conformations: Mentioned as a more advanced topic.

Double and Triple Bonds

• Trans-2-butene (Double Bond): Sp2 hybridized with ~120° bond angles.
• 2-butyne (Triple Bond): Sp hybridized with 180° bond angles, straightforward representation.

Converting Skeletal Structures to Other Forms

• Understanding Structure: Number carbons, consider visible bonds.
• Hydrogen Calculations: Use the formula 4 minus visible bonds.
• Molecular Formulas: Condense groups for simplified representations.

Inclusion of Heteroatoms

• Example: Ethanol: Show bonds to non-carbon atoms explicitly.
• Example: Butanamide: Include bonds to O and N atoms with their respective hydrogens.

Practice and Applications

• Further Practice: Recommended quizzes available on Leah4Sci website.

Conclusion

• Efficiency in Representation: Skeletal structures save time and simplify understanding.
• Continuous Practice: Essential for mastering the representation of organic molecules.