2nd LE

• Solubility refers to the capability of a solid, liquid, or gaseous chemical substances, named solute, to dissolve in a solvent which is usually a liquid and form a solution.
• solubility is affected by 4 factors:

  • temperature
  • pressure
  • polarity
  • molecular size
• Hydrocarbons are soluble in CH2Cl2 but insoluble in water because they are non-polar organic compounds; CH2Cl2 is non-polar while H2O is polar; like dissolves like
• Hydrocarbons have no reaction with dilute base (NaOH).
• Alkenes are reactive with cold concentrated sulfuric acid (sulfonation).
• Halogenation/ bromination

  Reagent: Br2

  Positive Result: loss of red-orange color of Br2
• Bromination is a chemical reaction where bromine (Br₂) is added to a hydrocarbon. This reaction can proceed through different mechanisms depending on the type of hydrocarbon and the conditions (light or dark).
• Reagent and Solvent for Halogenation/ Bromonation

  • Br₂ (Bromine): A red-orange liquid that reacts with hydrocarbons.
  • CH₂Cl₂ (Dichloromethane): Used as a solvent. It's non-polar and inert, meaning it does not react with the bromine or the hydrocarbons. It helps dissolve bromine and bring it into contact with the hydrocarbons.
• Positive Result for Halogenation/ Bromination

  • Loss of Red-Orange Color: Indicates that bromine has reacted with the hydrocarbon. Bromine’s color disappears because it is consumed in the reaction.
• Halogenation/ Bromination Reaction Mechanisms

  • Light Reaction: In the presence of light, bromination proceeds via a radical mechanism.
  • Dark Reaction: Without light, bromination typically proceeds via an electrophilic addition mechanism for alkenes and alkynes.
• Free radical substitution (FBS)

  • requires light
  • produce HBr as one of the product
  • mechanism by which alkanes and alkyl benzene undergo bromination
  • toluene undergoes bromination at a faster rate despite the fact that its is brominated at a primary carbon. this is explained by resonance stabilization of benzyllic free radical.
  • stability of free-radical: benzyllic > 3° > 2° > 1° > CH3
  • ease of formation of the free-radical: benzyllic > 3° > 2° > 1° > CH3
• Electrophilic Addition (EA)

  • can take place even in the dark
  • no HBr is produced
  • mechanism by which alkenes and alkynes are produced are brominated
  • stability of carbonation: benzylic > 3° > 2° > 1° > CH3
• • Baeyer's Test: This test is used to distinguish between saturated and unsaturated hydrocarbons based on their reactivity with cold, dilute, neutral potassium permanganate solution.
• Reaction Mechanism for Baeyer's Reagent: Baeyer's reagent oxidizes unsaturated hydrocarbons, causing the permanganate ion (MnO₄⁻) to be reduced to manganese dioxide (MnO₂), resulting in the color change from purple to brown.
• Baeyer's Reagent and Reaction

  • Reagent: Cold, dilute, neutral KMnO₄ (potassium permanganate).
  • Positive Result: Disappearance of purple color of permanganate solution and formation of brown precipitate (MnO₂).
• Terminal Alkynes: Alkynes with a triple bond at the end of the carbon chain are called terminal alkynes. They react with ammoniacal silver nitrate due to the presence of a reactive hydrogen atom.
• Reaction with Ammoniacal AgNO3

  Reagent:

  • Ammoniacal AgNO₃ or Ag(NH₃)₂⁺: Silver nitrate (AgNO₃) complexed with ammonia (NH₃). It's often called "ammoniacal silver nitrate."

  Positive Result:

  • Formation of Insoluble Substance or Gray Precipitate: Indicates the presence of terminal alkynes.
• Reaction with Ammoniacal AgNO3

  • actually an acid-base reaction, not an oxidation
  • used to detect presence of terminal alkynes
• Preparation of Acetelyne Gas

  CaC2​+2H2​O→C2​H2​+Ca(OH)2​