TOPIC 5 ORGANIC CHEMISTRY

Instructors: Syed Abdul Illah Alyahya, Syed Abd Kadir Hazlini Mohmad Ameran, Dr. Aimi Suhaily Saaidin, Dr. Hairunnisa Ramli
Institution: Centre of Foundation Studies, UiTM

CONTENT

5.1 Introduction to Organic Chemistry
5.2 Isomerism
5.3 Hydrocarbons
5.4 Alkyl Halides
5.5 Alcohols
5.6 Aldehydes and Ketones
5.7 Carboxylic Acids and Its Derivatives

5.1 INTRODUCTION TO ORGANIC CHEMISTRY

Lesson Outcomes

Upon completion of this topic, students should be able to:

• Classify organic molecules based on their functional groups.
• Draw structural formulae in the form of expanded, condensed, and skeletal structures.
• Explain covalent bond cleavage: homolytic fission (formation of free radicals) and heterolytic fission (formation of ions).
• Explain a molecule/species acting as an electrophile or nucleophile in electrophilic addition.

Characteristics of Carbon

• Carbon's ability to form single, double, and triple bonds with other carbon atoms allows it to create chains of varying lengths, known as catenation.
• Carbon can form cyclic or ring structures.
• Carbon can bond with other atoms including O, S, N, P, halogens, and metals.

5.1.1 Homologous Series and Functional Groups

• Organic molecules can be classified based on their functional groups and categorized according to homologous series.
• Functional group: An atom or group of atoms within a molecule responsible for the molecule’s chemical behavior. The chemical behavior of a functional group is consistent, regardless of the molecule's size or structure.

Characteristics of Homologous Series

1. Compounds in the same homologous series can be represented by the same general formula.
2. They possess the same functional groups and chemical properties.
3. They can be synthesized using similar methods.
4. Successive members differ by a -CH₂ group.
5. Physical properties (e.g., boiling point, density) change progressively with increasing molecular mass.

Examples of Functional Groups and Corresponding Homologous Series

5.1.2 Representation of Organic Molecules

Structural Formula Representations

1. Expanded Structural Formula: Displays each atom and the specific covalent bonds (double or triple) within the molecule.
2. Condensed Structural Formula: Represents atom arrangement in a linear sequence, where bonds are often omitted. For large repeating units (-CH₂-), units can be enclosed in parentheses.
3. Skeletal Structural Formula: Shorthand representation where carbon and hydrogen covalent bonds are depicted as lines.
4. 3D Structural Formula: Depicts the three-dimensional spatial arrangement of atoms or groups using wedge-dash diagrams:
      - Wedged line: Bond projects in front of the plane of the paper toward the viewer.
      - Dashed line: Bond lies behind the plane of the paper, away from the viewer.
      - Solid line: Bond lies in the plane of the paper.

Practice 2

Illustrate an expanded structural formula for each of the following compounds:
(a) Propane (C₃H₈)
(b) Butanol (C₄H₁₀O)
(c) Pentanoic acid (C₅H₁₀O₂)

Practice 3

Illustrate the condensed structural formula for each of the following compounds:

5.1.3 Organic Chemistry Reactions

Homolytic and Heterolytic Fissions and the Mechanistic Arrows

• Homolytic fission occurs in nonpolar covalent bonds, evenly breaking the bond such that each atom receives one shared electron, resulting in free radicals. A half-headed arrow indicates the movement of a single electron.
• Heterolytic fission occurs in polar covalent bonds and breaks unevenly. One atom retains both electrons (becoming anions), while the other loses both electrons (becoming cations). A full-headed arrow denotes the movement of a pair of electrons.

Nucleophiles and Electrophiles

• Nucleophiles (Nu-): Electron-rich species that can donate an electron pair (Lewis bases). Examples include negative ions, lone pairs of electrons, hydroxide ions, and compounds with multiple bonds.
• Electrophiles (E+): Electron-poor species that can accept an electron pair (Lewis acids). Examples consist of positive ions, some double-bonded electronegative components, and carbocations.

Free Radicals

• Free radicals are species (atoms, ions, or molecules) that contain one or more unpaired electrons in their outer shell. They can be formed via homolytic fission of a covalent bond. An example is .CI + .CI.

Types of Organic Reactions

1. Addition Reactions: Two reactants combine to form one product (A + B → AB). Includes electrophilic and nucleophilic additions.
2. Elimination Reactions: One reactant splits into two products (AB → A + B). Typically produces a small molecule (e.g., H₂O, HBr).
3. Substitution Reactions: Two molecules exchange an atom or a group of atoms (AB + C → AC + B).
4. Rearrangement Reactions: A molecule undergoes changes in how its atoms are connected (A-B- A → B-A-A).

(Continuing this exhaustive documentation of Organic Chemistry, including everything from Hydrocarbons to Carboxylic Acids and their derivatives.)