Writing Structural, Condensed, and Skeleton Formulas for Organic Compounds

Introduction

• Organic chemistry requires different structural representations compared to general chemistry.
• Molecular Formula: Indicates the types and numbers of atoms in a compound (e.g., C4H10) but not the arrangement.

Structural Formula

• Purpose: Shows how atoms are connected and the attachment pattern.
• Steps to Draw:
  1. Count carbon atoms in the molecular formula.
  2. Arrange carbon atoms in a row (carbon backbone).
  3. Add hydrogen atoms to complete four bonds per carbon.
• Examples:
  • CH4: One carbon with four hydrogens.
  • C2H6: Two carbons each with three hydrogens.
  • C3H8: Three carbons, end carbons with three hydrogens, middle with two.

Practice Problems

• Write structural formulas for:
  • C4H10: Four carbons, end carbons with three hydrogens, middle carbons with two.
  • C8H18: Eight carbons, same pattern as above for end and middle carbons.

Condensed Formula

• Definition: Simplified structural representation, omits covalent bonds.
• How to Write:
  • List attached atoms after the central carbon in order.
  • Use parenthesis for identical groups attached to the same atom.
• Examples:
  • C3H8 as CH3CH2CH3.
  • For branched chains, use parentheses to indicate attachment.

Converting Between Formulas

• From Condensed to Structural:
  • Begin with the first carbon and its hydrogens.
  • Chain successive carbons, ensuring four bonds per carbon.
  • Identify double/triple bonds.
• Examples:
  • CH3CH2CH3: Draw as a chain with respective hydrogens.

Skeleton Formula

• Purpose: Represents carbon skeleton, omits hydrogen atoms unless part of a functional group.
• Drawing Rules:
  • Angles/beginnings/ends represent carbon atoms.
  • Double/triple bonds shown as double/triple lines.
• Examples:
  • Linear chains represented by zigzag lines.
  • Benzene as a hexagon with alternating double bonds or a circle.

Practice Problems

• Convert structural formulas to skeleton and vice versa.

Conclusion

• Understanding these formulas is crucial for identifying structures and understanding molecular interactions in organic chemistry.