Lecture on Drawing Constitutional Isomers

Introduction

• Topic: Drawing Constitutional Isomers in Organic Chemistry
• Previous Topics: Naming alkanes, drawing conformations of alkanes
• Future Topics: Newman projections, conformations of cycloalkanes (e.g., cyclohexane chair conformation)

Channel Introduction

• Host: Chad from Chad's Prep
• Goal: Make science understandable and enjoyable
• Series: Weekly organic chemistry lessons for 2020-21
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Understanding Hydrocarbons

• Saturated vs. Unsaturated Hydrocarbons

  • Saturated: Max hydrogens possible, formula CnH2n+2
  • Unsaturated: Contains pi bonds/rings, reduces hydrogen count
  • Example: C7H16 (saturated) vs. C7H14 (unsaturated)

• Degrees of Unsaturation

  • Every pi bond or ring removes 2 hydrogens from saturation
  • Hydrogen Deficiency Index: (2C + 2 - H - Hal + N) / 2 = Degrees of Unsaturation

Drawing Constitutional Isomers

• Saturated Hydrocarbons (C7H16 Example)

  • No pi bonds or rings
  • Start with longest chain and reduce step by step

• Methods for Drawing Isomers

  • Start with the longest chain (7 carbons)
  • Reduce to 6, 5, 4 carbons while adding branches
  • Avoid end placement for branches to ensure new isomers
  • Unique positions for branches on middle carbons

Detailed Example: Drawing Isomers for C7H16

• 7 carbon chain: Simple straight chain
• 6 carbon chain: Explore positions for single carbon branches
• 5 carbon chain:
  • Add two branches (methyl groups) in different positions
  • Consider single ethyl group placement
• 4 carbon chain: Limited options, fill 3 out of 4 middle positions

Incorporating Oxygen (C4H10O Example)

• Understand how oxygen does not affect the saturation calculation

• Oxygen Placement

  • Can form alcohols (OH group) or ethers (O in chain)

• Alcohols: Oxygen bonded at different locations

  • On end carbons or 1 carbon in

• Ethers: Oxygen between carbons

  • Divide carbons as 3-1 or 2-2 across the oxygen

Conclusion

• Total Isomers for C4H10O: 7 (4 alcohols, 3 ethers)
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