1 / 24

c10 k

Lecture Outline . Aromatic vs aliphatic compoundsBenzeneStructure/ stabilityElectronic configurationThe concept of aromaticityHuckel's ruleAromatic compounds other than benzeneNomenclature of benzene derivatives. Aromatic/ Aliphatic compounds. Aromatic compounds have a low hydrogen-carbon ratioe.g. benzene, benzaldehydeAliphatic compounds have a higher ratioe.g. alkanes, alkenes, alkynes.

bernad
Download Presentation

c10 k

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


    1. C10 K Aromatic Chemistry Lecture 1 Dr. Gallimore

    2. Lecture Outline Aromatic vs aliphatic compounds Benzene Structure/ stability Electronic configuration The concept of aromaticity Huckel’s rule Aromatic compounds other than benzene Nomenclature of benzene derivatives

    3. Aromatic/ Aliphatic compounds Aromatic compounds have a low hydrogen-carbon ratio e.g. benzene, benzaldehyde Aliphatic compounds have a higher ratio e.g. alkanes, alkenes, alkynes

    4. Examples of Aromatic compounds Benzaldehyde Naphthalene Coal Benzo[a]pyrene

    5. Buckminsterfullerene

    6. BENZENEStability of the ring The difference in energy between benzene and the hypothetical cyclohexatriene is called the resonance energy. The resonance energy is the energy lost (stability gained) by complete delocalization of electrons in the pi system. It is a measure of the added stability of the aromatic system compared to the localized system

    7. Reactivity of benzene More energy is required for a reaction in which the aromatic character of the ring is lost Does NOT undergo addition of HX, X2 Does NOT oxidize with KMnO4

    8. Benzene is a resonance hybrid of the contributing structures Each carbon atom is at the corner of a regular hexagon All C-C bond lengths are identical (1.39 Angstroms)

    9. Bonding in benzene

    10. The Concept of AromaticityRequirements for aromaticity Molecule must be cyclic Molecule must be planar Each atom of the ring(s) must have a p-orbital perpendicular to the plane of the ring Huckel’s rule must be obeyed Planar compounds must have (4n + 2) pi electrons, where n is an integer Ring with 2, 6, 10 or 14 pi electrons may be aromatic Ring with 8, 12 or 16 pi electrons will not be aromatic

    11. For aromaticity, all pi electrons must be paired and all bonding orbitals filled Maximum and complete overlap is required for stabilization With unpaired pi electrons, overlap is not maximized The pi electrons in an aromatic compound are delocalized over the entire ring leading to stabilization

    13. Bonding in Cyclooctatetraene

    14. Bonding in Cyclopentadiene

    15. The Cyclopentadienyl anion

    16. The Cyclopentadienyl cation

    17. Antiaromatic compounds The pi-electron energy of a compound is determined by experimentation and calculations The pi electrons in an aromatic compound are delocalized over the entire ring leading to stabilization Ring has lower pi electron energy than the open chain In antiaromatic compounds, the ring has a greater pi-electron energy than the open chain

    18.

    19. Nomenclature Substituents are added as prefixes to benzene e.g. bromobenzene Derivatives of benzene Common names are often used in the naming of some benzene derivatives

    21. The benzene ring is numbered when more than two substituents are present The ring is numbered to give the lowest possible number to the substituents When more than two different substituents are present, they are listed alphabetically.

    22. If substituted benzenes (e.g. aniline or toluene) are used as the parent, that substituent is understood to be at position 1 on the ring.

    23. The designation phenyl is used when benzene is being treated as a substituent. The phenylmethyl group is designated benzyl.

    24. Next Lecture Electrophilic aromatic substitution (EAS) Mechanism of EAS Specific examples of EAS Aromatic nitration Aromatic sulfonation Aromatic halogenation Friedel-Crafts alkylation and acylation

More Related