unit 7

Cards (26)

  • Aromatic compounds
    Class of compounds that contain six-membered benzene-like rings with three double bonds
  • Early aromatic compounds
    • benzaldehyde (from cherries, peaches, and almonds)
    • toluene (from Tolu balsam)
    • benzene (from coal distillate)
  • Benzene (C6H6)
    • Has eight fewer hydrogens than alkane (C6H14) and is clearly unsaturated
    • A six-membered ring with alternating double and single bonds
    • All C-C-C bond angles are 120°
    • All six carbon atoms are sp2-hybridized
    • Each carbon has a p orbital perpendicular to the plane
  • Benzene causes leukopenia on prolonged exposure and should not be used as laboratory solvent
  • Major source of aromatic compounds
    Coal and Petroleum
  • Pharmaceutical preparations
    • Steroids (e.g. estrone, Lipitor)
    • Benzene
  • Aromatic compounds are generally nonpolar and immiscible with water
  • Aromatic compounds are often unreactive, making them useful as solvents for other nonpolar compounds
  • Due to their high ratio of carbon to hydrogen, aromatic compounds are characterized by a sooty yellow flame
  • benzene
    Less reactive than alkenes because of their resonance
  • Cyclohexene reacts rapidly with Br2
    Gives the addition product 1,2-dibromocyclohexane
  • Benzene reacts slowly with Br2
    Gives the substitution product C6H5Br
  • Benzene
    The "circle" representation must be used carefully since it doesn't indicate the number of π electrons in the ring
  • Hückel's rule for aromaticity
    • Molecule must have a planar, monocyclic system of conjugation
    • It must contain a total of 4n + 2π molecules where n is an integer n = 0,1,2,3...
    • Molecules with 2, 6, 10, 14, 18 .... π electrons can be aromatic
    • Antiaromatic - planar conjugate molecule with 4nπ electrons (4,8,12,16)
  • Electrophilic aromatic substitution
    A process in which an electrophile (E+) reacts with an aromatic ring and substitutes for one of the hydrogens
  • Mechanism of electrophilic bromination of benzene
    Reaction occurs in two steps and involves a resonance-stabilized carbocation intermediate
  • Other electrophilic aromatic substitution reactions
    • Aromatic halogenation (fluorination, chlorination, iodination)
    • Aromatic nitration
    • Aromatic sulfonation
  • Substituents affect the reactivity and orientation of a reaction
    • Substituents can be classified as meta-directing deactivators, ortho-para directing deactivators, and ortho-para directing activators
  • Ortho
    Substituents at the 1 and 2 positions on an aromatic compound, adjacent to the primary carbon
  • Meta
    Substituents at the 1 and 3 positions on an aromatic compound
  • Para
    Substituents at the 1 and 4 positions on an aromatic compound, directly opposite the primary carbon
  • Activating groups
    Donate electrons to the ring, making it more electron-rich, stabilizing the carbocation intermediate, and lowering the activation energy
  • Deactivating groups
    Withdraw electrons from the ring, making it more electron-poor, destabilizing the carbocation intermediate, and raising the activation energy
  • Iodination
    biosynthesis of thyroxine (growth regulating hormone)
  • Sulfonation
    mixture of SO3 and H2SO4
  • Friedel-crafts alkylation reaction
    treating aromatic with alkyl chloride