Organic Chemistry Review Lecture Notes

Introduction

• Semester review broken down by sections.
• Exam scheduled for Monday, December 2nd, 7:30-8:30 PM.
  • 60 minutes long, 35 multiple-choice questions.
  • No need to bring Scantrons, provided during exam.
  • Bring writing utensil, ID, and calculator (recommended).
  • Exam information available on Canvas.

Exam Preparation

• Focus on discussion questions from the semester.
  • Questions similar in structure to exam, but multiple choice.
  • Concept-based focus, e.g., mechanisms, polarity effects.

Key Concepts

Polarity and Thin Layer Chromatography (TLC)

• Nonpolar compounds: hydrocarbons (e.g., hexane, benzene).
• Polar compounds: carbon bonded to electronegative heteroatoms (e.g., ethyl acetate, dichloromethane).
• Very polar compounds: carbon-heteroatom and heteroatom-hydrogen bonds (e.g., acetic acid).
• Chromatography principles: separation based on polarity.
  • Stationary phase: polar, immobilized.
  • Mobile phase: relatively non-polar.
  • TLC: silica plate as stationary phase, nonpolar mobile phase.
  • Polarity affects movement through stationary and mobile phases.

Extraction Experiment

• Two layers: organic (neutral organic compounds) and aqueous (inorganic salts, organic salt).
• Example: Benzoic acid becomes charged in basic solution, moving to aqueous layer.
• Solvent density affects layer positioning (most organics less dense, chlorinated solvents more dense).

Column Chromatography

• Similar to TLC, but for purification.
• Polar stationary phase (silica), nonpolar mobile phase.
• Use TLC to determine solvent system for column.
• Compound order in column reflects TLC results.

Recrystallization

• Purification technique.
• Solvent should not react chemically, dissolve compound when hot, not when cold.
• Impurities: insoluble remain solid, soluble dissolve.
• Melting point analysis for purity.
  • Pure compounds: narrow melting range.
  • Impurities: broaden range, lower melting point.

Natural Products Isolation

• Extraction of limonene from orange peels via microwave.
• Use of TLC to identify presence of limonene.
• Comparison with standards to determine presence.

Nucleophilic Substitution

• SN1: Unimolecular, two-steps, flat intermediate, stereochemistry scrambling.
• SN2: Bimolecular, one-step, inversion of stereochemistry.
  • Transition state with leading group leaving as nucleophile attacks.

Alkene Addition and Epoxide Formation

• Limonene + NBS forms bromohydrin.
• Multi-step process involving epoxide formation.
• Use of gas chromatography and mass spectrometry for analysis.
  • Differences in isotope distribution for bromine and chlorine.

Elimination

• Dehydration of cyclohexanol to cyclohexene.
• Distillation used for purification.
• Qualitative bromine and permanganate tests for analysis.
  • Positive bromine test: disappearance of bromine color.
  • Positive permanganate test: disappearance of purple, formation of brown precipitate.

Additional Notes

• Focus on conceptual understanding for the exam.
• Safety considerations should be noted for experiments.
• Use of discussion questions and lab materials for study.
• Resources: lab manual, post-lab videos, online resources like Khan Academy.