CHE1C1B organic chemistry lecture notes weeks 1 - 4

CHEMISTRY 1B Lecture Notes: Introduction to Organic Chemistry

Organic Chemistry

• Definition: Organic Chemistry is the study of carbon compounds, specifically focusing on those that have a covalent carbon backbone which is pivotal in forming complex molecules essential for life.

• Importance: It encompasses a wide variety of substances, ranging from simple molecules like methane to complex structures like DNA.

Key Elements in Organic Compounds

• In addition to carbon (C) and hydrogen (H), organic compounds frequently incorporate other elements:

  • Oxygen (O): Found in alcohols, carboxylic acids, and ethers.

  • Nitrogen (N): Present in amines, amides, and nucleic acids.

  • Halogens (e.g., fluorine, chlorine): Often substituents in organic molecules that can affect reactivity.

  • Sulfur (S) and Phosphorus (P): Essential in biochemical compounds like ATP (adenosine triphosphate) and proteins.

Complex Biological Systems

• Organic compounds are integral to countless natural products:

  • Perfumes: Derived from a variety of organic molecules, often esters and terpenes, which contribute to their scent.

  • Plastics: Synthetic polymers made from organic monomers (e.g., polyethylene, polystyrene).

  • Pharmaceuticals: Complex organic compounds designed to interact with biological systems for therapeutic effects.

Diversity of Organic Compounds

• Approximately 16 million natural or synthetic organic compounds have been identified, exhibiting vast diversity in structure and function. This diversity is a result of:

  • Different arrangements of carbon atoms (linear, branched, cyclic).

  • Variations in functional groups that impart distinct chemical properties.

Bonding Differences

• Organic compounds primarily display covalent bonding which allows for sharing of electrons, leading to:

  • Unique chemical properties and reactivities compared to inorganic compounds, which typically rely on ionic bonding.

  • Consequently, this leads to organic compounds characterized by slower reaction rates than typical ionic compounds.

Ionic vs. Covalent Bonding

Ionic Compounds:

• Formed through the transfer of electrons from metals to non-metals.

• Example: Sodium Chloride (NaCl) forms strong electrostatic attractions resulting in high melting and boiling points.

Covalent Compounds:

• Formed by the sharing of electron pairs between non-metal atoms.

• Example: Methane (CH4) comprises covalent bonds, which generally produce weaker polar attractions.

Structure of Hydrocarbon Compounds

1.1 Structure and Bonding of Organic Molecules

• Covalent Bonding Visualized: Visualizing bonding as electron sharing through the overlap of atomic orbitals helps explain molecular geometry.

• Example: Methane (CH4) has a tetrahedral shape with bond angles of 109.5 degrees, a result of sp³ hybridization.

1.2 Alkanes

• First 10 Alkanes: A series of saturated hydrocarbons.

  • Methane (CH4)

  • Ethane (C2H6)

  • Propane (C3H8)

  • Butane (C4H10): Contains two structural isomers: n-butane (straight chain) and isobutane (branched structure).

• Alkane Structure: Composed solely of sigma (σ) bonds, with all carbon atoms being sp³ hybridized.

1.3 Sigma and Pi Bonds

• Sigma (σ) Bonds: Formed by direct overlap of s-s, s-p, or p-p orbitals, representing the strongest type of covalent bond.

• Pi (π) Bonds: Created through the sidewise overlap of half-filled p orbitals, typically found in double and triple bonds.

  • Example: In ethene (C2H4), both sigma and pi bonds exist within its structure, contributing to its reactive properties.

1.4 Nomenclature of Alkanes

• IUPAC Naming: Governed by the longest continuous carbon chain rule. Prefixes indicate the number of carbons:

  • Meth- (1), Eth- (2), Prop- (3), But- (4), etc.

• Isomers: Compounds with identical molecular formulas but differing structural arrangements; example includes butane and isobutane.

1.5 Reactions of Alkanes

• Major types of reactions involving alkanes: Combustion (release of energy as heat and light) and Halogenation (substitution of hydrogen atoms with halogen atoms).

Functional Groups and Nomenclature

• Common functional groups include Esters, Amides, and Carboxylic Acids, which are derivatives of hydrocarbons and have their own unique properties and reactivities.

• Reactivity of Carboxylic Derivatives decreases in the following order: Acid Chlorides > Anhydrides > Esters > Amides.

Organic Reactions

• The processes of bond-breaking and bond-making define reaction mechanisms, with key types being:

  • Heterolytic and Homolytic Fission, which refer to how bonds break (unequally or equally).

  • Nucleophilic reactions where electron-rich species interact with electron-poor centers, and conversely, Electrophilic reactions, where electron-poor species seek out electron-rich sites.

Summary of Key Properties

• Hydrogen Bonding significantly affects the physical characteristics of compounds, such as boiling points and solubility:

  • Alcohols: Exhibit higher boiling points compared to alkanes due to the ability to form hydrogen bonds.

  • Alkanes: Generally exhibit lower water solubility, especially as their carbon chain lengthens.

Exercises

• Examples provided include various reactions, conversions, and derivations related to nomenclature and organic compound chemistry, ensuring practical application of concepts learned in class.