Chapter 6

• Saturated hydrocarbons


  Hydrocarbon having only single covalent bonds between their carbons

  
• Types of saturated hydrocarbons


  • Alkanes
  • Cycloalkanes

  
• Alkanes


  • Non-polar solvents
  • Subject to London dispersion forces
  • Have relatively low melting and boiling points
  • Immiscible in water but freely miscible in other non-polar solvents
  • Cannot break the strong hydrogen bond between water molecules

  
• Cycloalkanes


  • Saturated hydrocarbons that contain a ring in their carbon backbones
  • Have higher boiling points, melting points, and densities than alkanes
  • Unreactive with little or no ring strain
  • Exist as "Puckered rings"

  
• Alkanes


  • Methane
  • Ethane
  • Propane
  • Butane
  • Pentane
• Combustion of alkanes


  Converts alkanes to carbon dioxide and water
• Cracking of hydrocarbons


  Yields a mixture of smaller alkanes and alkenes at high temperatures

  
• Halogenation of alkanes


  1. Occurs with halogen in the presence of heat or light and through a radical mechanism

  2. Radicals are formed in initiation

  3. Radicals are consumed and formed in propagation

  4. Radicals are consumed in termination
• Halogenation of cycloalkanes


  Occurs in the presence of heat or light to form a halogenated cycloalkane
• Ring opening of cyclopropane


  1. Occurs with hydrogen halide to form 1-halopropane

  2. Occurs with halogen to give 1,3-dichloropropane

  3. Occurs with hydrogen to produce propane

  
• Ring opening of cyclobutane


  Occurs with hydrogen to produce butane
• Cis-trans isomerism


  Groups can be either on the same side of the ring (cis) or on opposite sides of the ring (trans)
• Cycloalkanes are represented as planar structures, and the positions of the groups are indicated as either above or below the plane of the ring

  
• Uses of saturated hydrocarbons


  • Fuels
  • Heating oils
  • Solvents
  • Rocket fuel
  • Refrigerants
• Alkanes are widely used as fuels, heating oils, and as solvents
• Methane, the simplest alkane, is used as a fuel in several automobiles, water heaters, and ovens. In its highly refined form, liquid methane can also serve as rocket fuel
• Several cryogenic refrigeration systems use ethane as a refrigerant
• Containing only C–C and C–H bonds, unreactivity of cycloalkanes with little or no ring strain are comparable to non-cyclic alkanes

  
• All of the cycloalkanes, from cyclopentane upwards, exist as "Puckered rings"

  
• Cyclohexane has a ring structure that looks like a puckered ring

  
• Compared to alkanes, cycloalkanes have higher boiling points, melting points, and densities due to stronger London forces because the ring shape allows for a larger area of contact

  
• Cycloalkanes feature a ring-shaped arrangement of sp3 hybridized carbon atoms

  
• Cycloalkanes with one ring have the chemical formula CnH2n >3

  
• Cycloalkanes can branch into side chains
• Alkanes are non-polar solvents since only C and H atoms are present

  
• Alkanes are subject to intermolecular forces called London dispersion forces

  
• Alkanes have relatively low melting and boiling points due to the weak intermolecular London dispersion forces
• Alkanes are immiscible in water but freely miscible in other non-polar solvents
• Alkanes consisting of weak dipole dipole bonds cannot break the strong hydrogen bond between water molecules, hence they are not miscible with water

  
• Combustion converts alkanes to carbon dioxide and water
• Cracking of hydrocarbons at high temperatures yields a mixture of smaller alkanes and alkenes

  
• Halogenation of alkanes occurs with halogen in the presence of heat or light and through a radical mechanism
• In the mechanism of halogenation, radicals are formed in initiation, consumed and formed in propagation, and consumed in termination
• Halogenation of cycloalkanes occurs in the presence of heat or light to form a halogenated cycloalkane
• Ring opening of cyclopropane occurs with hydrogen halide to form 1-halopropane, with halogen to give 1,3-dichloropropane, and with hydrogen to produce propane
• Ring opening of cyclobutane occurs with hydrogen to produce butane
• Cis-trans isomerism also occurs in cyclic compounds, where groups can be either on the same side of the ring (cis) or on opposite sides of the ring (trans)
• All cycloalkanes, from cyclopentane upwards, exist as "Puckered rings"

  
• Saturated hydrocarbons


  Hydrocarbon having only single covalent bonds between their carbons

  
• Types of saturated hydrocarbons


  • Alkanes
  • Cycloalkanes