Introduction to Organic Chemistry

Definition: Chemistry of carbon, hydrogen, and sometimes other elements (N, O, P, S, halogens). Initially thought to include only compounds found in living organisms, but now encompasses many synthetic compounds.

Hydrocarbons

Simplest organic compounds consisting only of carbon and hydrogen.

• Chemical Formula Example: Methane (CH₄)

• Structural Representations:

  • Condensed structural formula: CH₄

  • Skeletal diagram: A simple zigzag line representing carbon centers.

Hydrocarbons Properties

• Non-polar molecules, insoluble in water.

• Occurrence: Present in fossil fuels like coal, oil, and natural gas.

• Classification: Based on size, types of bonds (single, double, triple), and arrangements of carbons.

  • Alkanes (single bonds): Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈), Butane (C₄H₁₀).

  • Naming: Identify the longest continuous chain (parent chain) and branches using prefixes.

  • Example: 2-Methylbutane (C₅H₁₂) has a chain of four carbons with a methyl group attached to the second carbon.

Isomers

• Structural Isomers: Compounds with the same formula but different arrangements of bonds/atoms.

  • Example: Butane (C₄H₁₀) can exist as n-butane (linear structure) or isobutane (branched structure).

• Stereoisomers: Same bonding structure but different spatial arrangements (cis/trans).

  • Example: Cis-2-butene has both methyl groups on the same side, while trans-2-butene has them on opposite sides.

Functional Groups

• Alkyl Halides: Hydrocarbons with halogen atoms (F, Cl, Br, I).

  • Example: Bromomethane (CH₃Br).

• Alcohols: Hydrocarbons with hydroxyl (–OH) groups. Named by replacing "e" with "-ol".

  • Example: Ethanol (C₂H₅OH).

• Ethers: Two hydrocarbon groups bonded to an oxygen atom.

  • Example: Diethyl ether (C₂H₅)₂O.

Types of Hydrocarbons

• Alkenes: Unsaturated hydrocarbons with at least one double bond.

  • Example: Ethylene (C₂H₄).

  • Naming: Change the ending to "-ene" and specify double bond location (e.g., propene for C₃H₆ with the double bond between the first and second carbon).

• Alkynes: Unsaturated hydrocarbons with at least one triple bond.

  • Example: Acetylene (C₂H₂).

  • Naming: Change the ending to "-yne".

• Cycloalkanes: Hydrocarbons in ring structures, indicated with "cyclo-" prefix.

  • Example: Cyclopentane (C₅H₁₀).

• Aromatic Hydrocarbons: Contain a benzene ring, stable due to delocalized electrons.

  • Example: Benzene (C₆H₆).

Reactions of Hydrocarbons

• Alkanes: Non-reactive, can undergo combustion (complete/incomplete) and substitution reactions.

  • Example: Complete combustion of propane: C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O.

• Alkenes and Alkynes: More reactive; participate in addition reactions.

  • Example: Addition of HBr to ethylene: C₂H₄ + HBr → C₂H₅Br.

• Markovnikov's Rule: In addition reactions, the electrophile attaches to the more substituted carbon.

Carbonyl Compounds

• Aldehydes: Carbonyl group (C=O) at the end of the carbon chain, named by replacing "e" with "-al".

  • Example: Formaldehyde (HCHO).

• Ketones: Carbonyl group in the middle, named by replacing "e" with "-one".

  • Example: Acetone (C₃H₆O).

• Carboxylic Acids: Contain a carbonyl and hydroxyl group, weak acids; named by changing the ending to "-oic acid".

  • Example: Acetic acid (C₂H₄O₂).

• Esters: Derived from carboxylic acids and alcohols; named based on the alcohol and acid component.

  • Example: Ethyl acetate (C₄H₈O₂), from ethanol and acetic acid.

Amines and Amides

• Amines: Derived from ammonia; often have strong odors, named by changing the ending to "-amine".

  • Example: Methylamine (CH₃NH₂).

• Amides: Similar to esters, replace oxygen with nitrogen; named by changing the ending to "-amide".

  • Example: Acetamide (C₂H₅NO).

Properties and Reactions of Organic Compounds

• Properties: Governed by structure and functional groups; polar or non-polar characteristics determine solubility and reactivity.

• Reactivity: Varies across functional groups; many undergo substitution, addition, and elimination reactions.

Natural and Synthetic Polymers

Definition: Long chain-like molecules made of repeating units (monomers).

• Types:

  • Homopolymers: Composed of one type of monomer.

    • Example: Polyethylene (from ethylene monomers).

  • Copolymers: Composed of two or more types of monomers.

    • Example: Nylon (from hexamethylenediamine and adipic acid).

• Natural Polymers: Proteins, cellulose, starch, nucleic acids, etc.

• Synthetic Polymers: Polyethylene, nylon, etc.; produced through polymerization reactions.