Ch 21

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Ch 21
2013-01-13 21:36:38
Phenols Aryl Halides

Ch 21
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  1. (1) Hydroxybenzene, C6H5OH. (2) Family of compounds characterized by a hydroxyl group on an aromatic ring, ArOH.
  2. The reaction of a primary aromatic amine with nitrous acid, HNO2 , which forms a diazonium ion, R-N+≡N: and can be used to prepare aryl halides, phenols, and aryl cyanides, or to deaminate the amine.
    Diazotization of an amine
  3. Simple phenols, ArOH, are weak acids with pKa ≈ 10 and they are deprotonated by aqueous NaOH to form phenoxide anions, ArO-
    Phenols as weak acids
  4. Synthesis of an unsymmetrical ether by alkylation of an alkoxide anion, RO-, with a primary alkyl halide, R' X (or with an alkyl sulfate or alkyl sulfonate), which reacts by an SN2 mechanism: RO- + R' X → ROR' + X-
    Williamson ether synthesis
  5.  Replacement of a hydrogen on an aromatic ring by a strong electrophile. Also called SE2 reaction for Substitution, Electrophilic, Bimolecular.
    Electrophilic aromatic substitution
  6. Carboxylation of phenolate anions with carbon dioxide to form salicylic acids, or o-hydroxy benzoic acids
    Kolbe rxn
  7.  (1) The conversion of allyl phenyl ethers to o-allyl phenols by a sigmatropic rearrangement, which proceeds via a cyclohexadienone intermediate. (2) The conversion of allyl vinyl ethers to γ,δ-unsaturated carbonyl compounds by a sigmatropic rearrangement.
    Claisen rearrangement
  8. A derivative of cyclohexadienedione, usually 1,4-benzoquinone (para-quinone); oxidation of a 1,4-benzenediol (hydroquinone) derivative will produce a para-benzoquinone derivative.
  9. Two-stage substitution that involves addition and elimination reactions of an aromatic compound; in the addition stage, a nucleophile adds to the aromatic ring; in the elimination stage, a group is expelled from the aromatic ring. Also called SNAr reaction.
    Nucleophilic aromatic substitution
  10. Two-stage mechanism for a nucleophilic addition-elimination reaction; in the addition stage, the nucleophile adds to the carbon that bears the leaving group, then in the elimination stage, the leaving group is expelled.
    Nucleophilic addition-elimination mechanism
  11. A cyclohexadienyl anion that is resonance stabilized by delocalization of electrons, which is formed during a nucleophilic aromatic substitution (SNAr) reaction by an addition-elimination mechanism
    Meisenheimer intermediate
  12. Two-stage mechanism for a type of nucleophilic aromatic substitution reaction; in the first stage, an aromatic halide undergoes elimination to form a benzyne intermediate, then in the second stage, nucleophilic addition to the benzyne yields the product of the reaction
    Elimination-addition mechanism
  13. Dehydrobenzene, C6H4 , in which benzene lacks two hydrogens and has an additional pi bond that results from sideways overlap of two sp2 orbitals on adjacent atoms of the ring (usually drawn with a triple bond replacing a double bond); it is a very unstable and highly reactive aromatic intermediate, which is formed during a nucleophilic aromatic substitution (SNAr) reaction by an elimination-addition mechanism.
  14. A species that contains a triple bond within an aromatic ring, such as benzyne