Lecture 8: Ethers

Learning Objectives

  • Identify the ether functional group in given structures and predict expected chemical and physical properties.
  • Use IUPAC nomenclature rules to determine the correct systematic name of an ether given its structure.
  • Predict the product structure of an ether from:
    a. Acid-catalyzed dehydration of alcohols
    b. Williamson Ether Synthesis
    c. Alkoxymercuration-demercuration
  • Predict the products from reactions involving ethers:
    a. Acidic cleavage
    b. Autooxidation
  • Use reactions involving ethers to create synthetic pathways.

Ethers

  • Definition: Ethers are a class of organic compounds that can be characterized by the general structure containing an oxygen atom connected to two alkyl or aryl groups.
  • Properties of Ethers:
    • Generally unreactive compared to alcohols.
    • Commonly used in laboratories as polar, aprotic solvents.
    • Boiling point increases with the size of alkyl chains due to stronger intermolecular forces (IMFs).
  • Example Analysis:
    • When ranking compounds by boiling points, one must consider the types of intermolecular interactions:
    • Dispersion forces
    • Dipole-dipole interactions
    • Hydrogen bonding (present in alcohols but not in ethers)
    • Interpretation of energy changes related to intermolecular forces when assessing boiling points should factor in how increased size corresponds to increased dispersion forces.

Nomenclature of Ethers and Epoxides

  • General Rules:
    • If multiple functional groups are present in a molecule, the functional group with the highest priority determines the base chain and naming sequence. Other groups (ethers, halogens, alkyls) are treated as substituents.
Functional Groups and Corresponding Formulas:
  • Carboxylic acid: RCOOH - Suffix: -oic acid
  • Acid anhydride: RCO-O-COR - Suffix: -oic anhydride
  • Ester: RCOOR' - Suffix: -oate
  • Acid chloride: RCOCl - Suffix: -oyl chloride
  • Amide: RCONR'R'' - Suffix: -amide
  • Nitrile: RCN - Suffix: -nitrile
  • Aldehyde: RCHO - Suffix: -al (common name: aldehyde)
  • Ketone: RCO-R' - Suffix: -one
  • Alcohol: R-OH - Suffix: -ol
  • Thiol: R-SH - Suffix: -thiol
  • Amine: R-NR'R'' - Suffix: -amine
  • Alkene: R-R' - Suffix: -ene
  • Alkyne: R-R' - Suffix: -yne
Naming Ethers

  • When Only Ether is Present in the Molecule:
    a. Identify the longest carbon chain as the base chain.
    b. Identify the shorter chain as a substituent, labeling it as “-oxy” instead of “-yl” (#-alkyloxy).
    c. For common naming, each branched alkyl group is named using the suffix “-yl,” with a final designation of “ether.”

  • When Multiple Functional Groups Are Present in the Molecule:
    a. Identify the most complex and longest chain as the base chain.
    b. Name the ether as a substituent using “-oxy.”
    c. Number the chains accordingly and include any stereochemistry before the main name.

Naming Examples
  • Example 1:
    • Compound structure: OEt, Br
    • IUPAC name: 1-ethoxyethane
    • Common name: diethyl ether
    • Compound structure: ethoxy
    • IUPAC: 2-ethoxy-3-methylbutane
    • Common name: ethyl 1,2-dimethylpropyl ether

Preparation of Ethers

  • 1. Acid-Catalyzed Dehydration of Alcohols:

    • A method to synthesize ethers by removing water from alcohols under acidic conditions.

  • 2. Williamson Ether Synthesis:

    • A synthetic route where an alkoxide reacts with a primary alkyl halide to form an ether.

  • 3. Alkoxymercuration-Demercuration:

    • A reaction that involves the addition of an alkoxy group to an alkene through an intermediate mercuric species, followed by demercuration to yield an ether.

Reactions with Ethers

  • General Reactivity:
    • Ethers are mostly unreactive under basic, neutral, or mildly acidic conditions.
Specific Reactions:

  • 1. Acidic Cleavage:

    • Involves breaking the ether bond under acidic conditions to yield alcohols or alkyl halides.

  • 2. Autooxidation:

    • Refers to the oxidative degradation of ethers, leading to the formation of hydroperoxides and alcohols, which can influence reactivity and stability.

Synthesis with Ethers and Epoxides

  • Example Creation:
    • The student is tasked to devise synthetic pathways based on the reactions and properties of ethers and epoxides rewritten from the initial compound transformations.