PC2M7

• Hydrocarbons


  Organic compounds consisting entirely of carbon and hydrogen atoms
• Types of hydrocarbons

  • Saturated
  • Unsaturated
  • Cycloalkane
• Saturated hydrocarbons


  • Contain only single bonds and are heavily laden with hydrogen
• Unsaturated hydrocarbons


  • Consist of a single, double or triple bond between carbon-carbon atoms
• Cycloalkanes


  • Possess one or multiple carbon rings, with hydrogen atoms attached to the carbon ring
• Types of hydrocarbons

  • Aliphatic
  • Aromatic
• Aliphatic hydrocarbons


  • Straight chain structures having no rings
• Aromatic hydrocarbons


  • Circularly structured organic compounds that contain sigma bonds along with delocalized pi electrons

  
• Hydrocarbons are nonpolar substances with weak intermolecular forces, low melting and boiling temperatures, and poor or no solubility in polar solvents
• Physical properties of aliphatic hydrocarbons

  • Gases (fewer than 5 carbon atoms, low volatility)
  • Liquids (5-15 carbon atoms, intermediate volatility)
  • Solids (more than 15 carbon atoms, high volatility)
• Volatility

  Hydrocarbons are volatile because they can evaporate easily into the air
• Boiling point of aliphatic hydrocarbons

  Higher boiling point with increased number of carbons/longer chain, increased molar mass
• Boiling point of aliphatic hydrocarbons

  Linear chain has higher boiling point than branched chain
• Melting point of aliphatic hydrocarbons

  Increased symmetry leads to higher melting point and lower boiling point
• Aromatic hydrocarbons are less dense than water, although they are usually more dense than other hydrocarbons.

  (Water > Aliphatic > aromatic)
• Halogenated benzene compounds are denser than water
• Aromatic hydrocarbons are insoluble in water and are used as solvents for other organic compounds
• London dispersion forces

  Weak intermolecular forces that operate between alkane molecules and provide enough attraction for them to exist as liquids as their molecular size increases
• Reactivity of aliphatic hydrocarbons

  • Alkanes (less reactive)
  • Alkenes (more reactive)
  • Alkynes (most reactive)
• Baeyer’s test

  Potassium permanganate is an oxidizing agent that reacts with unsaturated aliphatic hydrocarbons, but does not react with alkanes or aromatic hydrocarbons
• Aromatic compounds

  • Double bonds are less likely to participate in addition reactions than those found in typical alkenes
  • Composed of closed rings of delocalized electrons originating from alternative single and double bonds
  • Extremely stable due to aromaticity (additional stability provided by resonance)
• Aromatic hydrocarbons having multiple bonds are unsaturated in nature
• Bromine reaction

  1. Decoloration of bromine is often used as a test for a carbon-carbon double bond

  2. Alkenes react in the cold with pure liquid bromine, or with a solution of bromine in an organic solvent like tetrachloromethane

  3. Cyclohexene reacts with bromine in the same way and under the same conditions as any other alkene
• Nitration reaction

  • A process wherein a nitro group is added in an organic compound
  • Benzene will react with hot concentrated nitric acid to produce nitrobenzene
• Reactions of hydrocarbons

  • Substitution (arenes)
  • Addition (alkenes and alkynes)
  • Combustion
• Combustion of hydrocarbons

  1. Hydrocarbon reacts with oxygen to produce carbon dioxide, water, and heat

  2. Combustion of methanol, propane, ethene
• SINGLE CARBON BOND

  saturated and less reactive
• MULTIPLE CARBON BOND

  unsaturated and far more reactive
• ALIPHATIC CHEMICAL PROPERTIES

  • Known as saturated hydrocarbons because they only have single bonds between carbon and hydrogen atoms.
• ALKANE

  • React with a much greater variety of compounds than alkanes.
• Arene

  • Undergo substitution reactions, whereas alkenes and alkynes undergo addition reactions.
• BROMINE REACTION

  • test for unsaturation
• AROMATIC CHEMICAL PROPERTIES

  • Ratio of hydrogen atoms to carbon atoms is relatively high in these molecule types, When burned.
  • Aromatic hydrocarbons having multiple bonds are unsaturated in nature
• NITRATION REACTION

  • A process wherein a nitro group is added in an organic compound. Positive result is yellow oily substance called Nitrobenzene
• NITRATION OF BENZENE

  • Benzene will react with hot concentrated nitric acid to produce nitrobenzene
  • This reaction proceeds slowly(dangerous), since hot, conc. nitric acid is a powerful oxidizer, and organic compounds are easily oxidizable.
• A safer reaction involves a mixture of nitric and sulfuric

  • Sulfuric acid catalized reaction

  Sulfuric acid behaves as a catalyst, and allows this nitration reaction to proceed at a lower temperature and more quickly.
• The reaction mechanism is similar to an acid catalyzed dehydration.

  • Nitronium ion reacts with benzene

  The nitronium ion reacts with benzene to form the sigma complex, which then loses a proton to generate the aromatic product.
• METHYL ESTER

  • formed by the condensation of methanol & benzoic acid in the presence of strong acid.
  • Nitrating Methyl Benzoate with HNO3 using H2O4 as catalyst.
  • Nitrating the Benzene ring is an electrophilic aromatic substitution reaction.
• SUBSTITUTION REACTION

  • Arenes undergo substitution reactions, in which the aromatic hydrogen is replaced with an electrophile, hence their reactions proceed via electrophilic substitution.
• ADDITION REACTION

  • Addition reaction is restricted to only alkenes and alkynes.
  • It also involves many reagents situated across pi bonds like chlorine, and water.