CHEM 120: Chemical Reactivity

Course Overview and Textbooks

This course introduces the foundational concepts of organic chemistry, focusing on the structure, nomenclature, and reactivity of carbon-containing compounds. Recommended textbooks include Chemistry: The Central Science and Organic Chemistry by Bruice, Hart et al., and others.

• Primary Textbook: Chemistry: The Central Science: A Broad Perspective, 2nd Edition, Pearson

• Recommended Books: Organic Chemistry - A Short Course (Hart et al.), Organic Chemistry (Bruice), and other relevant organic textbooks

Organic Chemistry

Definition and Scope

Organic chemistry is the study of carbon-containing compounds and their properties. Most organic compounds feature chains or rings of carbon atoms, which can be found in a wide variety of natural and synthetic substances.

• Key Point 1: Organic compounds are primarily composed of carbon and hydrogen, often with oxygen, nitrogen, and other elements.

• Key Point 2: The structure of organic molecules can be linear, branched, or cyclic.

• Example: Glucose () and Ascorbic acid () are biologically important organic compounds.

Structure of Carbon Compounds

Hybridization and Geometry

Carbon atoms can form different types of bonds and geometries depending on their hybridization state. The three main hybridization states are sp3, sp2, and sp.

• sp3 Hybridization: Tetrahedral geometry, bond angle of 109.5°

• sp2 Hybridization: Trigonal planar geometry, bond angle of 120°

• sp Hybridization: Linear geometry, bond angle of 180°

Each carbon atom satisfies the octet rule by forming four covalent bonds.

Examples of Hybridization

• Methane (): All hydrogens are arranged tetrahedrally around the central carbon (sp3).

• Ethene (): Each carbon is sp2 hybridized, forming a planar structure.

• Ethyne (): Each carbon is sp hybridized, resulting in a linear molecule.

Hydrocarbons

Classification and Properties

Hydrocarbons are compounds composed solely of carbon and hydrogen. They are classified based on the types of bonds between carbon atoms.

• Alkanes: Saturated hydrocarbons with only single bonds. General formula:

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

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

• Aromatic hydrocarbons: Contain conjugated ring systems, such as benzene ()

Physical Properties

• Alkanes exhibit only van der Waals (London dispersion) forces.

• Boiling point increases with chain length.

• Combustion of hydrocarbons produces and .

Organic Nomenclature

Systematic Naming of Organic Compounds

Organic compounds are named using a systematic approach that includes a prefix, base, and suffix.

• Suffix: Indicates the type of compound (e.g., -ane for alkanes).

• Base: Specifies the number of carbons in the longest continuous chain.

• Prefix: Identifies substituents attached to the main chain.

Steps in Naming Alkanes

1. Determine the type of compound (suffix).

2. Find the longest carbon chain (base).

3. Number the chain from the end nearest the first substituent.

4. List substituents in alphabetical order, along with their position numbers.

5. If multiple substituents are present, use prefixes (di-, tri-, tetra-) but do not consider them for alphabetical order.

Examples of Alkane Names

Cyclic Alkanes

Ring Structures and Stability

Carbon atoms can also form ringed structures called cyclic alkanes. Five- and six-membered rings are the most stable due to their ability to adopt conformations close to the tetrahedral angle (109.5°).

• Smaller rings: More strained and less stable.

• Examples: Cyclopentane, cyclohexane

Naming Cyclic Alkanes

• Prefix the name with 'cyclo-' followed by the name of the alkane corresponding to the number of carbons in the ring.

• Substituents are named and numbered to give the lowest possible numbers.

Summary Table: Hybridization, Geometry, and Bond Angles

Additional info: The notes have been expanded to include systematic nomenclature steps, physical properties, and a summary table for hybridization and geometry, ensuring completeness and academic quality for exam preparation.