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Organic Chemistry: Ethers, Epoxides, and Sulfides

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  • What functional group characterizes ethers?
    Ethers contain an oxygen atom connected to two alkyl or aryl groups, represented as R–O–R'.
  • How do the boiling points of ethers compare to alcohols and hydrocarbons?
    Ethers have boiling points lower than alcohols of similar molecular weight but close to those of hydrocarbons of comparable weight.
  • Why are ethers more soluble in water than hydrocarbons?
    Ethers are hydrogen bond acceptors due to lone pairs on oxygen, increasing their water solubility compared to hydrocarbons.
  • What is the Williamson Ether Synthesis?
    An SN2 reaction between an alkoxide ion and a haloalkane to form dialkyl ethers, best with methyl or primary halides.
  • Why does Williamson Ether Synthesis fail with tertiary halides?
    Tertiary halides undergo β-elimination (E2) instead of substitution, preventing ether formation.
  • Describe the acid-catalyzed dehydration method for ether synthesis.
    Primary alcohols undergo intermolecular dehydration in acid to form symmetrical ethers, with protonation, nucleophilic attack, and deprotonation steps.
  • What is an epoxide?
    An epoxide is a cyclic ether with a three-membered ring containing one oxygen atom.
  • How are simple epoxides named?
    Simple epoxides are named as derivatives of oxirane or by adding the prefix epoxy if part of a larger ring.
  • How is ethylene oxide industrially synthesized?
    By passing ethylene and oxygen over a silver catalyst, producing oxirane (ethylene oxide).
  • What is the halohydrin method for epoxide synthesis?
    Alkenes react with halogen and water to form halohydrins, which undergo intramolecular base-induced SN2 displacement to form epoxides.
  • What is the common laboratory method for epoxide synthesis from alkenes?
    Oxidation of alkenes with peroxycarboxylic acids (e.g., m-CPBA) to form epoxides stereospecifically.
  • What does stereospecific epoxidation mean?
    The stereochemistry of the alkene is retained in the epoxide; cis-alkenes give meso epoxides, trans-alkenes give enantiomeric epoxides.
  • Why can't the epoxidation mechanism involve ionic intermediates?
    Because the reaction occurs in nonpolar solvents and proceeds with retention of alkene stereochemistry, no charged intermediates form.
  • Why are epoxides reactive in ring-opening reactions?
    The ring strain in the three-membered epoxide ring makes it susceptible to nucleophilic attack and ring opening.
  • Describe acid-catalyzed ring opening of epoxides.
    Protonation of the epoxide oxygen increases electrophilicity; nucleophilic attack occurs at the more substituted carbon with anti stereochemistry.
  • What is the product of acid-catalyzed hydrolysis of an epoxide?
    A trans-1,2-diol (glycol) is formed due to anti opening of the epoxide ring.
  • What are sulfides (thioethers)?
    Sulfides are sulfur analogs of ethers, with sulfur bonded to two alkyl or aryl groups, R–S–R'.
  • How are symmetrical sulfides prepared?
    By treating sodium sulfide (Na2S) with two equivalents of a haloalkane via nucleophilic substitution.
  • How are unsymmetrical sulfides synthesized?
    By converting a thiol to its sodium salt and reacting it with a haloalkane, analogous to Williamson ether synthesis.
  • What is a disulfide?
    A molecule containing an —S—S— bond, named as an alkyldisulfanyl substituent in IUPAC nomenclature.
  • How are sulfides oxidized?
    Treatment with hydrogen peroxide forms sulfoxides; further oxidation with NaIO4 yields sulfones.