Organic Chemistry Exam Review Notes

Overview

• Topics covered: Stereochemistry, SN2, SN1, E1, E2 reactions, and reactions of alkenes and alkynes.

Naming Compounds

Example Compound: Cyclohexane

• Structure: Cyclohexane with:
  • Bromine on carbon 1 (1-bromo)
  • Methyl on carbon 2 (2-methyl)
• Name: 1-bromo-2-methylcyclohexane

Chiral Centers

Chiral Center at Carbon 1

• Priority Determination:
  1. Bromine (highest atomic number) - Group 1
  2. Tertiary Carbon (connected to three carbons) - Group 2
  3. Secondary Carbon - Group 3
  4. Hydrogen - Group 4
• Configuration:
  • Order: 1 → 2 → 3 is counterclockwise ➔ S
  • H is in front ➔ Reverse ➔ R configuration
• Result: 1-R

Chiral Center at Carbon 2

• Groups:
  • Hydrogen - Group 4
  • Tertiary Carbon with Bromine - Group 1
  • Secondary Carbons - Group 2 and 3
• Configuration:
  • Order: 1 → 2 → 3 is clockwise ➔ R configuration
• Result: 2-R

Final Answer: 1-R, 2-R, 1-bromo-2-methylcyclohexane

Reaction Mechanisms

Converting 3-Methyl-1-butene to 3-Methyl-2-butanol

• Identify reagents:
  • A: BH3-THF + H2O2 e.g. Hydroboration-oxidation - Not suitable (adds to less substituted C)
  • B: Mercury acetate + NaBH4 → Correct answer (Markovnikov addition)
  • C: H2SO4 + H2O → rearrangement possibility
  • D: MCPBA + H3O+ → yields diol (anti-addition)
  • E: OsO4 + NaHSO3 → yields syn-diol

Major Substitution Product with Alkyl Halide and Methanol

• Conditions favor SN1 mechanism (secondary alkyl halide in polar product solvent).
• Carbocation formation and rearrangement:
  • Form unstable cyclic structure leading to more stable tertiary carbocation.
• Solvolysis occurs (methanol as nucleophile).
• Result: Methoxy-1-methylcyclopentane.

Reaction Rates

True/False Statements

• SN2 Reaction: Rate doubles with doubles nucleophile concentration ➔ True
• E1 Reaction: Rate triples with triple alkyl halide concentration ➔ True
• E2 Reaction: Rate increases sixfold with double substrate and triple base concentration ➔ True
• SN1 Reaction: Rate does not depend on nucleophile concentration ➔ False (It's the substrate concentration)

Identifying Chiral Molecules

Analysis of Choices

• A: No chiral centers (symmetric)
• B: No chiral centers (symmetric)
• C: Not chiral (two identical groups on one side)
• D: Chiral (no symmetry)

Chiral Molecule: D

E2 Reaction Mechanism with One Methyl Cyclohexene

• Hydroboration-Oxidation:
  • Anti-Markovnikov addition of hydroxide.
  • Syn addition of deuterium and hydroxyl group.
• Result: Correct answer based on deuterium position relative to methyl group (positioning and stereochemistry).

Major Product Predictions

Example of Alkene and Alcohol Reaction

• Key interaction of alkene with bromine leading to cyclic bromonium ion formation.
• Oxygen’s attack on the tertiary carbon forms a six-membered ring.
• Final product obtained after base abstraction of hydrogen.

Conclusion

• Always consider stereochemistry and regioselectivity in reactions.