Characteristics and Physical Properties of Alkenes and Unsaturated Hydrocarbons

Hydrocarbons and their Natural Sources

  • Unsaturated Hydrocarbons: This category includes alkenes, alkynes, and arenes (aromatic compounds). All of these substances contain carbon-carbon multiple bonds.

6.3.1 Alkenes or Olefins

  • Definition: Alkenes are characterized as unsaturated hydrocarbons that contain at least one carbon-carbon double bond.
  • Nomenclature: These compounds are identified by the −ene-\text{ene} ending in their names.
  • Synonyms: Alkenes are also commonly known as olefins.
  • Homologous Series General Formula: They are represented by the general formula C,H2nC,H_{2n}, where n=2,3,4,...n = 2, 3, 4, \text{...}

A. Homologous Series of Alkenes

  • Ethene (CH2=CH2CH_2=CH_2):

    • Description: Ethene is the simplest alkene.
    • Industrial Importance: It is among the most important industrial chemicals. It serves as a starting material for the synthesis of various industrial compounds, including:
      • Ethanol
      • Ethylene oxide
      • Ethanal
      • The polymer polyethylene
    • Natural Occurrence: Ethene occurs in nature as a plant hormone. It is produced naturally by fruits such as tomatoes and bananas and is directly involved in the ripening process of these fruits.

  • Propene (CH3−CH=CH2CH_3-CH=CH_2):

    • Industrial Importance: Propene is a vital industrial chemical used in the production of the polymer polypropylene.
    • Synthesis Applications: It acts as the starting material for the synthesis of acetone and cumene, in addition to other various industrial uses.

Table 6.4: The Homologous Series of Alkenes and Their Physical Constants

  • Ethene:

    • Molecular Formula: C2H4C_2H_4
    • Condensed Formula: CH2=CH2CH_2=CH_2
    • Melting Point (M.P.M.P.): −169-169
    • Boiling Point (B.P.B.P.): −102-102
    • Density: 0.61 g dm−30.61\,g\,dm^{-3}

  • Propene:

    • Molecular Formula: C3H6C_3H_6
    • Condensed Formula: CH2=CH2CH3CH_2=CH_2CH_3
    • Melting Point (M.P.M.P.): −185-185
    • Boiling Point (B.P.B.P.): −48-48
    • Density: 0.61 g dm−30.61\,g\,dm^{-3}

  • 1-butene:

    • Molecular Formula: CHCH
    • Condensed Formula: CH2=CH2CH2CH3CH_2=CH_2CH_2CH_3
    • Melting Point (M.P.M.P.): −130-130
    • Boiling Point (B.P.B.P.): −6.5-6.5
    • Density: 0.63 g dm−30.63\,g\,dm^{-3}

  • 1-pentene:

    • Molecular Formula: C5H10C_5H_{10}
    • Condensed Formula: CH2=CH2(CH2)2CH3CH_2=CH_2(CH_2)_2CH_3
    • Melting Point (M.P.M.P.): −130.5-130.5
    • Boiling Point (B.P.B.P.): 3030
    • Density: 0.64 g dm−30.64\,g\,dm^{-3}

  • 1-hexene:

    • Molecular Formula: C6H12C_6H_{12}
    • Condensed Formula: CH2=CH2(CH2)3CH3CH_2=CH_2(CH_2)_3CH_3
    • Melting Point (M.P.M.P.): −138-138
    • Boiling Point (B.P.B.P.): 6363
    • Density: 0.67 g dm−30.67\,g\,dm^{-3}

  • 1-heptene:

    • Molecular Formula: CHCH
    • Condensed Formula: CH2=CH(CH2)4CH3CH_2=CH(CH_2)_4CH_3
    • Melting Point (M.P.M.P.): −119-119
    • Boiling Point (B.P.B.P.): 9393
    • Density: 0.69 g dm−30.69\,g\,dm^{-3}

  • 1-octene:

    • Molecular Formula: CH 16CH\,16
    • Condensed Formula: CH2=CH(CH2)5CH3CH_2=CH(CH_2)_5CH_3
    • Melting Point (M.P.M.P.): −104-104
    • Boiling Point (B.P.B.P.): 122122
    • Density: 0.72 g dm−30.72\,g\,dm^{-3}

  • 1-nonene:

    • Molecular Formula: C9H18C_9H_{18}
    • Condensed Formula: CH2=CH2(CH2)6CH3CH_2=CH_2(CH_2)_6CH_3
    • Melting Point (M.P.M.P.): −95-95
    • Boiling Point (B.P.B.P.): 146146
    • Density: 0.73 g dm−30.73\,g\,dm^{-3}

  • 1-decene:

    • Molecular Formula: C10H20C_{10}H_{20}
    • Condensed Formula: CH2=CH2 (CH2)7CH3CH_2=CH_2\,(CH_2)_7CH_3
    • Melting Point (M.P.M.P.): −87-87
    • Boiling Point (B.P.B.P.): 171171
    • Density: 0.74 g dm−30.74\,g\,dm^{-3}