Organic Chemistry Exam Review Notes

Overview

• Topics covered in this lecture:
  • Stereochemistry
  • SN1, SN2, E1, E2 reactions
  • Alkene and alkyne reactions

Naming Compounds

• Example compound: Cyclohexane with bromine and methyl groups.
• Name: 1-bromo-2-methylcyclohexane
• Chiral centers:
  • Carbon 1:
    • Highest priority: Bromine (1)
    • Second: Tertiary carbon (2)
    • Third: Secondary carbon (3)
    • Hydrogen (4)
    • Configuration: R (counterclockwise direction)
  • Carbon 2:
    • Groups: Hydrogen (4), Primary carbon (3), Bromine-containing secondary carbon (1)
    • Configuration: R (clockwise direction)
• Final configuration: 1R, 2R, 1-bromo-2-methylcyclohexane

Reactions and Mechanisms

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

• Reagents:
  • A) BH3/THF + H2O2/OH- (not suitable)
  • B) Mercury acetate + water + sodium borohydride (correct answer)
  • C) Water + sulfuric acid (not suitable)
  • D) MCPBA (forms epoxide, not suitable)
  • E) OsO4 + NaHSO3 + H2O (syn addition, not suitable)

Major Product of Alkyl Halide with Methanol

• Secondary alkyl halide reacts under SN1 conditions.
• Mechanism: carbocation formation followed by solvolysis (methanol acting as nucleophile).
• Product: ether (methoxy-1-methylcyclopentane).

Rate Laws and Concentration Effects

• SN2 Reactions:
  • Rate depends on substrate and nucleophile concentration.
• E1 Reactions:
  • Rate depends only on substrate concentration.
  • Concentration of nucleophile does not affect rate.

Identifying Chirality

• Chiral Molecule Conditions:
  • No plane of symmetry.
  • Each chiral center must have four different substituents.
• Example answer: D is chiral.

Products from Reactions

1-Methylcyclohexene with Hydroboration Oxidation

• Reagents: BH3 followed by H2O2/OH-
• Mechanism: Syn addition to less substituted carbon.
• Final product: Hydroxyl group on less substituted carbon; methyl group on the opposite side.

Major Product from E2 Reaction

• Conditions: Hydroxide abstracts hydrogen adjacent to bromine.
• Product: E-isomer (due to anti-periplanar hydrogen and bromine).

Other Reactions

• 1-Butyne to 2-Butanone
  • Use of mercury sulfate with sulfuric acid (correct choice).

Conclusion

• Key takeaways:
  • Understand stereochemistry configurations (R/S).
  • Familiarize with reaction mechanisms and product outcomes.
  • Use of appropriate reagents for specific transformations.