Organic Chemistry Practice Problems Lecture

Overview

• Focus on practice problems for organic chemistry exams
• Topics include addition reactions, organic synthesis, and reaction mechanisms

Bromination of Alkenes

• Anti-Addition of Bromine
  • Break pi bond
  • Attach bromine atoms across the double bond
  • Anti-addition ensures opposite stereochemistry

Radical Halogenation

• Alkane Reaction with Bromine (Light Conditions)
  • Forms alkyl halide
  • Bromine attaches to more substituted carbon
  • Major product determined by substitution level

Nucleophilic Substitution and Elimination Reactions

• Reaction with Sodium Methoxide
  • Tertiary alkyl halide reacts
  • Sodium methoxide: strong nucleophile and base
  • Competition between SN2 and E2
  • E2 favored with tertiary alkyl halide
  • Forms most substituted alkene as major product

Ether Synthesis via Substitution

• Retrosynthetic Analysis
  • Convert tertiary alkyl halide to ether
  • Use weak nucleophile for SN1 mechanism
  • Replace halide with methoxy group

Addition Reactions

• Hydrogen and Hydroxy Group Addition
  • Anti-Markovnikov addition
  • Hydrogen attaches to more substituted carbon
  • Hydroxy group to less substituted carbon

Tosylate Conversions

• Conversion to Good Leaving Group
  • Use tosyl chloride and pyridine
  • Converts alcohol to tosylate
  • Potassium t-butoxide: bulky base, drives E2 mechanism

Markovnikov vs Anti-Markovnikov Additions

• Hydroxy Group Additions
  • Markovnikov: Hydroxy to more substituted carbon
  • Anti-Markovnikov: Bromine to less substituted carbon

Ozonolysis

• Oxidative Cleavage of Alkenes
  • Break double bond
  • Form two carbonyl fragments

Synthetic Strategy

• Ether Formation
  • Strong nucleophile with alkyl halide (SN2)
  • Deprotonate alcohol to form alkoxide

Radical Mechanism

• Steps: Initiation, Propagation, Termination
  • Initiation: Bromine splits into radicals
  • Propagation: Alkyl radical formation and product generation
  • Termination: Radicals combine to end reaction

Mechanisms of Reactions with Bromine

• Bromonium Ion Formation
  • Attack of bromine on alkene
  • Formation of bridge structure
  • Nucleophile attacks from opposite side

Practical Synthesis Problems

• Working Backwards for Synthesis
  • Identify target product
  • Break down into simpler components (retrosynthetic approach)

Alcohol to Alkene Conversion

• Use of Strong Bases for Elimination
  • Form more substituted alkene (Zaitsev's Rule)

Reaction Mechanisms with Alcohols

• SN1 and E1 Mechanisms
  • Identify type of alkyl halide
  • Determine conditions for nucleophilic substitution or elimination

Notes on Specific Reactions

• Alcohols with Hydrogen Bromide

  • Protonation and formation of carbocation
  • SN1 pathway; bromide ion attacks

• Reaction with Phosphoric Acid

  • Protonation, formation of carbocation
  • Base abstracts proton, forms alkene (E1 mechanism)