Bond Line Structures Lecture

Overview

• Bond line structures, also known as line-angle structures.
• Part of molecular representations in organic chemistry.
• Efficiency in representing organic molecules by not drawing all carbons and hydrogens.

Key Concepts

Representation

• Vertices: Each vertex represents a carbon atom.
• Lines: Each line represents a bond.
• Hydrogens: Not typically drawn if bonded to carbon, except in special cases (e.g., aldehyde functional group).
• Heteroatoms: Any atom other than carbon and hydrogen is labeled; hydrogens bonded to heteroatoms are shown.
• Lone Pairs: Typically not shown on heteroatoms but required in exam settings.

Drawing Bond Line Structures

• Carbon Atoms: Not drawn, represented by vertices.
• Hydrogens: Add hydrogens to complete the four bonds around carbon.
• Formal Charge: Indicated if present on structures.

Examples

1. Neutral Carbons: Have four bonds, missing bonds shown with hydrogens.
2. Carbocation: Carbon with a positive formal charge, often three bonds and no lone pairs.
3. Carbanion: Carbon with a negative formal charge, three bonds, and a lone pair.

Conversion Between Structures

• Lewis Structures to Bond Line: Identify longest carbon chain, zigzag for bond angles.
• Condensed Formulas: Use Lewis structure as an intermediary to convert to bond line structures.

Specific Example Insights

• Double Bonds: Represent with correct angles reflecting geometry.
• Triple Bonds: Ensure 180° bond angles are shown.

Practical Application

• Interconvert between Lewis structures, condensed formulas, and bond line structures.
• Convert structures while maintaining accuracy in bond angles and presence of lone pairs where necessary.

Additional Notes

• Practice drawing both cis and trans isomers for structures with double bonds.
• Typical exams require lone pairs to be shown.
• Radical structures (unpaired electrons) must be marked, differentiate from charged structures.

Final Advice

• Get in the habit of including lone pairs on heteroatoms, even when not required for bond line structures in professional contexts.
• Recommended to practice interconversion by first sketching Lewis structures.