Condensed Structures in Organic Chemistry

Jul 12, 2024

Lecture on Condensed Structures in Organic Chemistry

Introduction

  • Topic: Molecular representations and resonance
  • Upcoming Topics:
    • Functional groups
    • Chemical reactivities and molecules
    • Resonance
  • Playlist Info: Weekly lessons throughout 2020-21 school year

Condensed Structures

  • Basics:
    • Focus on carbon as the backbone of most molecules
    • Hydrogen atoms listed immediately after the carbon they are bonded to
    • Example: Carbon bonded to three hydrogens (CH3), next carbon, two hydrogens, etc.
    • Neutral carbon typically forms four bonds

Drawing Condensed Structures to Lewis Structures

  • Convert condensed structures to Lewis structures
  • Remember typical bonding configurations:
    • Halogens and hydrogen: 1 bond
    • Oxygen: 2 bonds
    • Nitrogen: 3 bonds
    • Carbon: 4 bonds
    • Adjust for formal charges if necessary

Using Parentheses in Condensed Structures

  • Three Main Uses of Parentheses:
    1. Repeating CH2 Groups:
      • Also called methylene groups
      • Example: (CH2)_3 to denote three methylene groups
    2. Multi-Atom Branches:
      • Not for single atoms like halogens
      • Example: CH(Br)CH3, indicating a branch with Br
    3. Multiple Identical Branches:
      • Example: CH(C2H5)_2, indicating two identical branches
      • Only for multi-atom branches

Pi Bonds in Condensed Structures

  • Adding Pi Bonds:
    • Identify if atoms lack a full octet
    • Assign double or triple bonds accordingly
    • Examples:
      • Double bond: CH3-CH2-CH=CH-CH3
      • Triple bond: CH3-CH-C≡C-CH3

Oxygen in Condensed Structures

  • Behavior of Oxygen:
    • Typically forms two bonds, can be in the chain or as a branch
    • Default assumes middle of chain unless atoms don't achieve filled octet
    • Examples:
      • Ketones: R-CO-R where oxygen is double-bonded in the chain
      • Carboxylic acids: R-COOH where -OH is a branch off the chain

Summary

  • Condensed structures efficiently represent molecular structures
  • Parentheses help condense repetitive or branched structures
  • Pi bonds and oxygen placements are key for proper structure visualization
  • Importance of recognizing typical bonding patterns and adjusting for formal charges