Organic Chemistry Reactions Crash Course

1. Cracking of Long-Chain Hydrocarbons

• Problem: Long-chain hydrocarbons from crude oil are large, viscous, low flammability, high melting/boiling point.
• Solution: Break into smaller, more flammable, lower viscosity, lower melting/boiling point molecules.
• Conditions:
  • Catalytic cracking: Zeolite catalyst (aluminum silicate), 500°C.
  • Thermal cracking: 450-700°C, 70 atm pressure.
• Products: Alkanes, alkenes, hydrogen; random process, must account for all original atoms.

2. Free-Radical Substitution

• Applicable to: Alkanes and any carbon-hydrogen chain.
• Example: Reaction of propane with chlorine using UV light or sunlight.
• Features: Hydrogens are substituted with chlorine, forming HCl as a byproduct.
• Reagents: Chlorine or bromine; fluorine reactions are too explosive, iodine reactions are too slow.
• Mechanism Knowledge Required: Essential for detailed understanding.

3. Electrophilic Addition of Alkenes

• Reactions include:
  • Bromination: Alkene reacts with Br₂, double bond becomes single, bromine atoms attach. Requires absence of light.
  • Hydrogenation: Alkene reacts with H₂, forms alkanes with added hydrogen. Requires nickel/platinum catalyst, 150°C.
  • Hydration: Alkene reacts with water, forms alcohol. Requires phosphoric/sulfuric acid catalyst, 300°C, 60 atm.
  • Hydrogen halides: Similar mechanism as above, requires concentrated HX (HBr, HCl, HI).
• Markovnikov’s Rule: In unsymmetrical alkenes, the hydrogen atom bonds to the carbon with more hydrogen atoms.

4. Oxidation of Alkenes

• Mild Oxidation: Using KMnO₄ in cold, dilute, alkaline conditions, forms diols.
• Strong Oxidation: Using hot, concentrated, acidified KMnO₄, breaks double bonds entirely:
  • Scenario 1: Carbon with two hydrogens forms CO₂ and water.
  • Scenario 2: Carbon with one hydrogen forms carboxylic acid.
  • Scenario 3: Carbon bonded to two carbons forms ketone.

5. Addition Polymerization of Alkenes

• Process: Thousands of alkene monomers form polymers under high pressure/temperature.
• Examples:
  • Polyethylene from ethene.
  • PVC from chloroethene.
  • Teflon from tetrafluoroethylene.

6. Nucleophilic Substitution of Haloalkanes

• With Aqueous NaOH (Reflux): Halogen replaced by OH⁻.
• With NaCN (Ethanolic): Halogen replaced by CN⁻. Increases carbon chain length.
• With NH₃ (Ethanolic): Halogen replaced by amine group.
• Mechanisms:
  • SN2: Primary haloalkanes.
  • SN1: Tertiary haloalkanes.

7. Elimination Reactions

• Haloalkanes: Form alkenes via loss of halogen and hydrogen from adjacent carbons. Conditions: Ethanolic NaOH, reflux.

8. Substitution Reactions of Alcohols

• With Halogens: OH replaced by halogen (Cl, Br, I).
• Methods:
  • Dry HCl gas, SOCl₂, PCl₅.
  • PBr₃, PI₃ for bromine/iodine substitution.

9. Reactions of Alcohols

• With Sodium: Forms alkoxide salt, releases hydrogen gas. Slow reaction, identifies alcohols.
• Esterification: Alcohol + carboxylic acid forms ester + water. Requires concentrated H₂SO₄ and reflux.
• Hydrolysis of Esters: Reversal of esterification, forming alcohols and carboxylic acids.

10. Dehydration of Alcohols

• Forms Alkenes: Removal of OH and adjacent H forms double bond. Conditions: Al₂O₃ catalyst, heat.

11. Oxidation of Alcohols

• Primary Alcohols: Oxidized to aldehydes, then to carboxylic acids. Reagents: Acidified K₂Cr₂O₇, reflux.
  • Distillation used to isolate aldehydes.
• Secondary Alcohols: Oxidized to ketones.
• Tertiary Alcohols: Resistant to oxidation.

12. Reduction of Carbonyl Compounds

• Reagents: LiAlH₄, NaBH₄.
• Processes:
  • Carboxylic acids to alcohols.
  • Aldehydes to primary alcohols.
  • Ketones to secondary alcohols.

13. Nucleophilic Addition of Aldehydes and Ketones

• With HCN: Forms cyanohydrins, requires NaCN and H₂SO₄.

14. Testing for Carbonyl Compounds

• 2,4-DNPH Test: Forms orange precipitate with carbonyls.
• Iodoform Test: Identifies methyl ketones, produces yellow CHI₃ precipitate.

15. Hydrolysis of Nitriles

• Forms Carboxylic Acids: Breaks CN bond, forming carboxylic acid and NH₄⁺ (or similar depending on conditions).

16. Reactions of Carboxylic Acids

• With Metals: Forms salt and hydrogen.
• With Bases/Metal Oxides: Forms salt and water.
• With Carbonates: Forms salt, water, and CO₂.
• With Ammonia: Forms ammonium salt.