OCHEM II CH17

Chapter 1: Introduction to Aromatic Compounds

• Overview of Aromatic Compounds

  • Focus on Chapter 17 from the David Klein textbook.

  • Material is pertinent for Exam 2.

  • Benzene is a prime example, known for having six pi electrons in a stable conjugated ring structure.

• Common Aromatic Compounds

  • Toluene: Benzene with one methyl group.

  • Xylenes: Benzene with two methyl groups can be ortho, meta, or para.

  • These compounds are prevalent in various pharmaceuticals.

• Source of Aromatic Compounds

  • Obtained from heating coal or petroleum.

  • Distillation of these materials yields compounds like benzene and toluene, each with specific boiling points.

• Naming Aromatic Compounds

  • Common names vs. IUPAC names:

    • Common names include toluene, phenol, and benzaldehyde.

    • IUPAC names tend to use a systematic approach, such as chlorobenzene and nitrobenzene.

  • Identifying the position of substituents is crucial for correct nomenclature (e.g., 1-chlorobenzene).

Chapter 2: Nomenclature and Structure

• Aromatic System Recognition

  • The parent compound is the one with the longest carbon chain compared to the aromatic ring.

  • Example: Ethylbenzene vs. phenyl groups.

• Identifying Substituent Positions

  • Importance of identifying positions to accurately name compounds.

  • Ortho (1,2), meta (1,3), and para (1,4) designations for substituted benzenes.

• Common Names and IUPAC Names

  • Recognition of both common and IUPAC names is essential (e.g., ortho-xylene vs. 1,2-dimethylbenzene).

Chapter 3: Aromaticity and Stability

• Criteria for Aromaticity

  • Must be cyclic, planar, and fully conjugated with a Huckel number of pi electrons (2, 6, 10, etc.).

  • Distinctions between aromatic, anti-aromatic, and non-aromatic systems.

• Examples of Aromatic and Non-Aromatic Compounds

  • Describing structures like pyridine and analyzing their aromaticity.

  • Importance of π electron counting: Examples highlighting counts for different ring systems.

• Molecular Orbitals and Resonance

  • Visual representation of molecular orbitals shows overlaps affecting stability.

  • Conjugation leads to enhanced stability preventing certain reactions (e.g., bromination fails with benzene).

Chapter 4: Reactions of Aromatic Compounds

• Substitution Reactions

  • Discuss mechanisms such as SN1 and E1 for reactions at benzyl positions.

  • Commonality of electrophilic aromatic substitutions (EAS) involving substitutions at aromatic rings.

• Physical Properties

  • Discussion of boiling points and solubility of benzene derivatives, understanding their reactivity.

  • Recognizing specific patterns and trends in substitution and addition reactions involving aromatic compounds.

Chapter 5: Functionalization of Aromatic Rings

• Side Reactions and Mechanisms

  • Primary focus on functional groups like -OH (alcohols) and -NO2 (nitro groups), and their impact on aromaticity.

  • Utilizing reagents such as potassium permanganate for oxidations.

  • Electrophilic addition reactions highlighted with specific substrates and predict outcomes accordingly.

• Impact of Substituents

  • Influence of electron-donating and withdrawing groups on reaction pathways and stability.

  • Birch reduction as a transformation pathway of aromatic compounds into alkenes.

Chapter 6: Polycyclic Aromatic Compounds

• Understanding Complex Structures

  • Aromatic compounds with multiple rings (such as naphthalene) and their stabilization energies compared to monochromatic counterparts.

  • Characteristics of anti-aromatic compounds contrasted with their mono-aromatic counterparts.

• Chemical Reactivity

  • Discussion of how different ring sizes and structures influence reactivity and stability.

Chapter 7: Summary and Conclusion of Aromatic Compounds

• General Properties Recap

  • Reactivity patterns discussed including electrophilic substitutions and the impacts of substituents.

  • Conclude with rules for identifying aromatic compounds, emphasizing key structural requirements for aromaticity, including the importance of electron counting.

Exam Preparation

• Focus on Key Reactions and Nomenclature

  • Review of common names, reactions, and functional groups relevant to the exam.

  • Emphasize familiarity with Huckel's rule and its implications.

  • Revision of structural representations (e.g., resonance forms and molecular orbitals).