Organic Chemistry Notes

Organic Chemistry

Basics

• Organic: Derived from living matter.
• Hydrocarbons: Organic compounds containing only carbon and hydrogen.
  • Carbon forms 4 covalent bonds.
  • Hydrogen forms 1 covalent bond.
• Homologous Series: Family of compounds with similar structure, same general formula, and similar chemical properties due to the same functional group.
• Functional Group: Atom or group of atoms determining chemical properties.

Families of Organic Compounds

• Alkanes
• Alkenes
• Alcohols
• Carboxylic Acids

Naming

• Two parts: Prefix (number of carbons) + Suffix (functional group).
• Carbon atoms:
  • 1: Meth-
  • 2: Eth-
  • 3: Prop-
  • 4: But-
  • 5: Pent-
• Functional groups:
  • Alkanes: -ane
  • Alkenes: -ene
  • Alcohols: -ol
  • Carboxylic acids: -oic acid
• Saturated: Alkanes with all single carbon-carbon bonds.

Alkanes

• General formula: CnH{2n+2}
• Saturated hydrocarbons.
• Unreactive except in combustion and substitution by chlorine.
• First four members (C1 to C4) are gases, next (C5 to C17) are liquids, heavier are viscous liquids or solids.

Chemical Reactions of Alkanes

• Combustion: Burning in air.
  • Complete combustion produces CO2 and H2O.
  • Incomplete combustion produces CO and H_2O.
  • Conditions for cracking:
    • High temperature (approximately 500°C).
    • High pressure.
    • Suitable catalyst.
• Cracking: Breaking down large molecules into smaller ones (alkanes and alkenes).
  • Can produce hydrogen gas from small alkanes, example: C2H6 \rightarrow C2H4 + H_2

Refining of Petroleum Oil

• Crude oil is a mixture of hydrocarbons.
• Refining includes fractional distillation and cracking.
• Fractional Distillation: Separating fractions based on boiling points.
• Cracking: Converts heavy alkanes to light alkenes, low energy fuels to high-value fuels, and inactive alkanes to active alkenes.

Alkenes

• General Formula: CnH{2n}
• Unsaturated hydrocarbons (contain double bonds).
• Active compounds, readily react by addition.

Differentiation between Alkanes & Alkenes

• Add bromine water (reddish brown).
  • Alkenes decolorize bromine water.
  • Alkanes do not decolorize bromine water; brown color remains.

Addition Reactions of Alkenes

• Breaking the double bond to form a single product.
• Reacts with halogens to decolorize bromine water.
• Reacts with steam to produce ethanol (hydration of ethene).

Comparing Alkanes and Alkenes

Alcohols

• General Formula: CnH{2n+1}OH
• Functional Group: -OH

The first 3 members of the alcohols homologous series are:

• Methanol: CH_3OH
• Ethanol: C2H5OH
• Propanol: C3H7OH

Preparation of Ethanol

• Hydration of Ethene: Catalytic addition of steam to ethene at 300°C and 6000 kPa using an acid catalyst.
  C2H4(g) + H2O(g) \xrightarrow{H3PO4} C2H_5OH (g)
  Note: Ethanol is flammable and has an aromatic (antiseptic) odor
• Fermentation of Glucose: Yeast is added to glucose at warm temperature (≈ 32°C).
  C6H{12}O6 (aq) \xrightarrow{yeast} 2 C2H5OH (l) + 2 CO2 (g)

Conditions for Fermentation

• Add water to form a solution of glucose.
• Add yeast.
• Warm temperature (30-35°C).
• Absence of air.

Uses of Ethanol

• Organic solvent
• Fuel

Carboxylic Acids

• General Formula: CnH{2n+1}COOH
• Functional Group: -COOH

The first 3 members of carboxylic acids homologous series are:

• Methanoic acid (Formic acid): HCOOH

• Ethanoic acid (Acetic acid): CH_3COOH

• Propanoic acid (Propionic acid): C2H5COOH

• Weak acids produced from the oxidation of alcohols.

• Turn litmus paper red (pH<7).

• Salts end with -oate.

• React with metals, alkali, base, and carbonate.

Polymerization

• Process where small molecules (monomers) link to form a large molecule (polymer).
• Monomer: Small molecule.
• Polymer: Large molecule made of repeating monomer units.

Addition Polymerization

• Monomer is an alkene (C=C bond).
• Double bond breaks, monomers link together.
• Example: Polymerization of ethene to polyethene.
  n (C=C) \rightarrow -[C-C]_n-

Examples and Differentiation

Examples of Polymers

Natural Polymers: Protein, Carbohydrates, Fats

Synthetic Polymers: Terylene, Nylon

Uses of Polymers

• Plastic bags, bottles, insulators.
• Nylon: Clothes, ropes.
• Terylene: Clothes.
• Protein and Carbohydrates: Food.

Advantages of Polymers

• Heat and electrical insulators.
• Does not rust.
• Unreactive, good strength.
• Recyclable.

Disadvantages of Polymers

• Disposal in landfills.
• Non-biodegradable.
• Toxic gases when burnt (e.g., HCl, CO).
• Recycling is expensive.