Isomerism

• Isomerism refers to compounds with the same molecular formula but different structures and properties. Isomers are classified into:
  1. Structural (Constitutional) – Different atomic connectivity.
  2. Stereoisomerism – Same connectivity, different spatial arrangement.

Structural isomerism

• Structural isomerism, also known as constitutional, is a form of isomerism where compounds share the same molecular formula but differ in the arrangement or connectivity of their atoms.
• This means that while structural isomers contain the same number and types of atoms, these atoms are connected in distinct ways, leading to variations in properties and reactivity.
• Structural is categorized into several types, each illustrating unique differences in atomic arrangement within molecules.

1. Chain Isomerism

• • Description:
    • Involves compounds with different arrangements of the carbon skeleton, which can manifest as straight chains, branched chains, or a mix of both.
  • Example:
    • C₅H₁₂ represents:
      • n-Pentane (straight-chain)
      • 2-Methylbutane (branched-chain)

2. Position Isomerism

1. 1. Description:

      • Occurs when compounds have identical molecular formulas and functional groups, but the functional groups are located at different positions on the carbon chain.

   2. Example:

      • C₃H₈O represents:
        • 1-Propanol (hydroxyl group on carbon-1)
        • 2-Propanol (hydroxyl group on carbon-2)

3. Functional Group Isomerism

• • Description:

    • Features compounds that share the same molecular formula but have different functional groups, leading to distinct chemical properties.

  • Example:

    • C₂H₆O represents:
      • Ethanol (alcohol, –OH functional group)
      • Dimethyl Ether (ether, –O– functional group)

4. Metamerism

• • Description:

    • Characterized by compounds with the same molecular formula and functional group but differing in the distribution of alkyl groups on either side of the functional group.
    • This type of isomerism is typical in ethers and esters.

  • Example:

    • C₄H₁₀O represents:
      • Diethyl Ether (CH₃CH₂-O-CH₂CH₃)
      • Methyl Propyl Ether (CH₃-O-CH₂CH₂CH₃)
    • These compounds exhibit metamerism due to the different alkyl group distributions around the oxygen atom.

5. Tautomerism

• • Description:

    • A unique form of structural isomerism where isomers can rapidly interconvert, typically through proton migration.
    • Tautomers coexist in equilibrium, influenced by environmental conditions like temperature and pH.

  • Example:

    • Acetone (C₃H₆O) predominantly exists in the keto form, but a minor fraction can be found in the enol form (an adjacent alcohol and carbon-carbon double bond), exemplifying keto-enol tautomerism.

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