Alkenes

Cards (21)

  • Alkene
    Like an alkane's wild younger brother, more reactive
  • Alkenes
    • Unsaturated hydrocarbons
    • Have the general formula CnH2n
    • Have at least one C=C double covalent bond
  • Examples of alkenes

    • Propene CH3CH=CH2
    • Buta-1,3-diene CH2=CHCH=CH2
  • Double bond

    Made up of a sigma (σ) bond and a pi (π) bond
  • Formation of sigma (σ) bond

    1. Two s orbitals overlap in a straight line
    2. Gives highest possible electron density between nuclei
    3. Results in a single covalent bond
  • Formation of pi (π) bond

    1. Sideways overlap of two adjacent p orbitals
    2. Electron density spread out above and below molecular axis
  • Sigma (σ) bonds have higher bond enthalpy than pi (π) bonds
  • Alkanes only have sigma (σ) bonds

    Alkanes don't react easily
  • Alkenes have both sigma (σ) and pi (π) bonds

    Alkenes are more reactive than alkanes
  • Alkenes are useful starting points for making other organic compounds and petrochemicals
  • Carbon atoms in a C=C double bond and attached atoms lie in the same plane (trigonal planar)
  • Atoms cannot rotate around C=C double bonds
  • Stereoisomers
    Molecules with the same structural formula but different arrangement in space
  • E/Z isomerism
    Type of stereoisomerism in alkenes due to restricted rotation around double bond
    1. isomer
    Alkene stereoisomer with same groups positioned across the double bond
    1. isomer
    Alkene stereoisomer with same groups positioned on the same side of the double bond
  • Determining E/Z isomers using Cahn-Ingold-Prelog (CIP) rules

    1. Look at atoms directly bonded to each C=C carbon
    2. Assign higher priority to atoms with larger atomic number
    3. Determine E/Z based on arrangement of higher priority groups
  • E/Z isomers can also be called cis-trans isomers
  • Cis means same groups on same side of double bond, trans means opposite sides</b>
  • Cis/trans naming system doesn't work if carbons have totally different groups attached
  • E/Z system still works even if carbons have different groups attached