Lecture Notes: Organic Chemistry

Announcements

• Upcoming Deadlines:

  • Active assignment 4 and Quiz 4 due this Friday.
  • New chapter content today will be on Active assignment 5.
  • Quiz 5 will be released later and is only multiple-choice, due earlier next week.
  • Grading for Quiz 3 is ongoing, expected to be completed tonight or tomorrow.

• Student Hours:

  • Wednesday: 11:30 to 1.
  • Thursday: Adjusted to 10 to 11:30.

Exam Preparation

• Exam scheduled for a week from Friday.
• Recommended to use TA office hours and SI study sessions for Q&A.

Alcohols to Alkyl Halides Conversion

• Converting alcohols to alkyl halides involves understanding the types of reactions:
  • SN1 Process: Using HBR might lead to a racemic mixture due to carbocation rearrangement.
  • SN2 Process: Preferred method to avoid rearrangement and ensure stereochemistry inversion.

Methods for Alkyl Bromides

• Use Phosphorus Tribromide (PBr₃):
  • Avoids rearrangement through an SN2 mechanism.
  • Three alcohols react with one PBr₃ producing three alkyl bromides and phosphonic acid.

Methods for Alkyl Chlorides

• Use Thionyl Chloride (SOCl₂) with Pyridine:
  • Similar to PBr₃, preferred over PCl₃ due to safety and effectiveness.
  • Pyridine deprotonates the alcohol intermediate.
  • Generates sulfur dioxide gas (SO₂), driving the reaction forward irreversibly.

Introduction to Ethers

• Structure: Oxygen sandwiched between two carbon groups.
• Properties:
  • Used primarily as solvents due to moderate polarity.
  • Less acidic and more volatile compared to alcohols.
  • Potential for forming explosive peroxides, especially upon exposure to light or heat.

Nomenclature

• Alkyl-Alkyl Ether Method:
  • Name based on alkyl groups (e.g., diethyl ether).
• Alkoxy Alkane Method:
  • Name based on the longer carbon chain with ether as a substituent (e.g., methoxy propane).

Synthesizing Ethers: Williamson Ether Synthesis

• Reaction:
  • Alcohol deprotonation followed by reaction with a primary alkyl halide.
  • Reagents: Sodium hydride (NaH) for deprotonation, alkyl halides for ether formation.

Mechanism

• Deprotonate alcohol with NaH.
• Nucleophilic substitution with alkyl halide to form ether.
• Primarily used for simple ethers and requires primary alkyl halides.

Next Steps

• Preparation for upcoming quizzes and assignments.
• Introduction to the next chapter on Ethers and Epoxides.
• Office hours available for additional support.