chm 102 handout

A Brief History of Organic Chemistry

  • Definition: Organic chemistry is the study of compounds containing carbon, typically with tetrahedral geometry.

  • Ancient Practices: The roots can be traced back to ancient medicine men who extracted chemicals from plants and animals for medicinal purposes, e.g., willow bark which contains acetylsalicylic acid (aspirin).

Development as a Scientific Discipline

  • Jon Jacob Berzelius (Early 1800s): First defined organic chemistry, classifying compounds into two groups:

    • Organic: Compounds originating from living or once-living matter.

    • Inorganic: Compounds derived from non-living sources (e.g., minerals).

  • Vitalism: Berzelius believed that organic compounds could only arise from living organisms through a "vital force."

Key Discoveries

  • Frederich Wöhler (1828): Landmark discovery that urea, an organic compound, can be synthesized from ammonium cyanate (an inorganic substance), undermining the theory of Vitalism.

    • Reaction: NH₄OCN (aq) → (NH₂)₂CO (urea).

  • Impact of Wöhler's Discovery:

    1. Introduced the idea of synthesizing organic compounds from inorganic sources.

    2. Led to further theories and chemical advancements, particularly in isomerism.

Evolution of Theories and Practices

  • By the 1860s: Chemists like Kékulé proposed theories relating chemical formulas to the physical organization of atoms in compounds.

  • Early 1900s: Focus shifted to the nature of chemical bonding, leading to the development of models for electron distribution.

  • Modern Developments: Organic chemistry has branched into many sub-disciplines such as polymer chemistry, pharmacology, and petrochemistry, with over 98% of known compounds being organic.

Nomenclature and Classes of Organic Compounds

  • Nomenclature: Essential for identifying the increasing number of organic compounds, estimated at over six million.

    • Guidelines:

      • Identify the longest carbon chain (base of name).

      • Determine the principal functional group and its position on the longest carbon chain.

  • Common Carbon Chains:

    • 1 Carbon: Meth-

    • 2 Carbons: Eth-

    • 3 Carbons: Prop-

    • 4 Carbons: But-

    • 5 Carbons: Pent-

    • 6 Carbons: Hex-

    • ... up to Dec- (10 Carbons).

Functional Groups and Their Naming

  • Principal Functional Groups:

    • Alkane: -ane

    • Alkene: -ene

    • Alkyne: -yne

    • Alcohol: -ol

    • Aldehyde: -al

    • Ketone: -one

    • Carboxylic Acid: -oic acid

Positioning in Organic Naming

  • The position of functional groups is numbered based on the carbon chain, with specific sulfur of suffix indicating the compound class.

  • Numbering Rules:

    • Positions are indicated through numbering, especially necessary in compounds with multiple functional groups.

    • Group prefix designations such as di-, tri-, tetra-, etc., are used for multiple identical groups.

Structure Representation

  • Shorthand Notation: For large organic structures, chemists use shorthand where carbon atoms are represented at inflections, and hydrogen atoms are typically omitted for simplicity.

Homologous Series and Hydrocarbons

  • General Formula for Alkanes: CₙH₂ₙ₊₂.

  • Types of Hydrocarbons:

    • Aliphatic Hydrocarbons (saturated & unsaturated)

    • Aromatic Hydrocarbons (reflect sweetness in scent, such as benzene).

Chemical Bonding in Organic Chemistry

  • Hybridization: A model used to explain the shape and bonding in organic compounds, specifically:

    • Sp³: tetrahedral geometry, occurs in alkanes.

    • Sp²: trigonal planar for alkenes.

    • Sp: linear for alkynes.

Alcohols and Their Properties

  • The reactivity of alcohols varies, with secondary and tertiary alcohols being more reactive compared to primary ones due to stability in carbocation formation.

Summary on Reactions and Synthesis

  • General Reaction Mechanisms involve fundamental additions, eliminations, and substitutions, and vary based on conditions of temperature or nature of substituents.

Conclusion

  • Understanding organic chemistry requires knowledge of the history, classification, nomenclature, and the fundamental properties of compounds and their reactions.