CHE102 organic notes

Page 1: Course Information

• Course Name: CHE102 General Chemistry II Notes

• Lecturers: Prof. Masesane

• Classrooms: 237/218

Page 2: Carbon in the Periodic Table

• Carbon in Periodic Table:

  • Group: 1A-8A (IA-VIIIA)

  • Atomic Number: 6

  • Atomic Mass: 12.011

• Valence Electrons: Carbon has four valence electrons, allowing it to form four bonds.

• Relationship to Other Elements: Combined with elements such as Hydrogen (H), Helium (He), Neon (Ne), and others in their respective groups.

Page 3: Classes of Hydrocarbons

• Major Classes:

  1. Alkanes (single bonds)

  2. Alkenes (double bonds)

  3. Alkynes (triple bonds)

  4. Arenes (aromatic compounds)

• Structural Examples:

  • Alkanes: H-C-H

  • Alkenes: C=C

  • Arenes: Involves one or more aromatic rings.

Page 4: Introduction to Organic Chemistry

• Definition: Study of carbon-containing compounds known as organic compounds.

• Role in Biological Molecules: Organic compounds form the basis of all life.

• Simple Carbon Compounds: Methane (CH₄) as an example, illustrates the concept of covalent bonding.

• Hybridization: Carbon can form four covalent bonds by promoting one electron from the 2s to the 2p orbital, resulting in an excited state.

Page 5: C-H Bond Lengths and Hybridization

• C-H Bond Characteristics: All four C-H bonds in methane are identical due to hybridization.

• Hybridization: Carbon is sp³ hybridized, resulting in:

  • 25% s-character

  • 75% p-character

• Molecular Geometry: The tetrahedral arrangement results in bond angles of 109.5°.

Page 6: Carbon-Carbon Bonds and Hybridization of Ethane and Ethene

• Carbon Bonds in Ethane: sp³ orbital overlap results in C-C and C-H bonds.

• Formation of C-C Double Bonds in Ethene: Hybridization into three sp² orbitals and one unhybridized p orbital leads to a planar molecule with bond angles of 120°.

Page 7: C-C Triple Bonds in Ethyne

• Triple Bonds Formation: Involves two sp orbitals and two unhybridized p orbitals leading to a linear structure with H-C-C angles of 180°.

• Planarity of Alkenes: Due to double bonding, alkenes have restricted rotation.

Page 8: Fractional Distillation of Crude Oil

• Definition: Separation of different hydrocarbons from crude oil.

• Major Types of Hydrocarbons: Alkanes, Alkenes, Alkynes, Aromatic Compounds.

• Cracking Process: Converts high molecular weight hydrocarbons to low molecular weight hydrocarbons.

Page 9: Straight Chain Alkanes

• General Formula: CₙH₂ₙ₊₂

• Examples:

  • Methane (CH₄)

  • Ethane (C₂H₆)

  • Propane (C₃H₈)

  • Butane (C₄H₁₀)

• Homologous Series: Series of organic compounds with similar functional groups, differing by one structural unit.

Page 10: Branched Chain Alkanes and Isomerism

• Isomers: Compounds with the same molecular formula but different structures.

• Naming Rules: Identify the longest chain, number from nearest substituent, identify substituents, and use -yl ending.

Page 11: Naming Branched Alkanes

• Numbering Convention:

  1. Number the longest chain from the end nearest a substituent.

  2. The substituent's position is included in the name.

  3. Multiple substituents use di-, tri-, tetra-, etc.

• Classification of Carbons:

  • Primary Carbon (1 other carbon)

  • Secondary Carbon (2 other carbons)

  • Tertiary Carbon (3 other carbons)

  • Quaternary Carbon (4 other carbons)

Page 12: Naming Cyclic Alkanes

• Cyclic Alkanes: Prefix „cyclo-“ added.

• Geometric Isomerism:

  • Cis: Substituents on the same side.

  • Trans: Substituents on opposite sides.

Page 13: Reactions of Alkanes

• Inertness: Generally unreactive except for combustion and free-radical halogenation.

• Combustion: Hydrocarbons react with oxygen to produce CO₂, H₂O, and energy.

• Halogenation Reactions: Substitution of hydrogen atoms with halogens.

Page 14: Free-Radical Halogenation Mechanism

• General Representation: Describes the sequence of bond breaking and making.

• Steps in Reaction:

  1. Initiation

  2. Propagation

  3. Termination

Page 15: Mechanism of Halogenation of Alkanes

• Overview: Occurs only on carbon atoms with at least one hydrogen.

• Example: Chlorination of ethane includes initiation, propagation, and termination steps.

Page 16: Alkenes Overview

• Definition: Hydrocarbons with double bonds between sp² carbons.

• Naming Convention: -ene suffix.

• Illustrations: Positional isomerism in alkenes with 4 carbons.

Page 17: Addition Reactions in Alkenes

• Reactions with Halides: Forms dihaloalkanes.

• Mechanisms: Carbocation stability affects reaction pathways.

Page 18: Reaction of H₂O with Alkenes

• Products: Water reacts with alkenes in the presence of an acid catalyst, forming alcohols.

• Markovnikov's Rule: Determines the formation of major products during reactions with asymmetric reagents.

Page 19: Naming Alcohols

• Structure: Derived from water by replacing a hydrogen with an alkyl group.

• Nomenclature: Replace -e with -ol. Example classifications based on carbon attachment: 1° alcohol, 2° alcohol, etc.

Page 20: Reactions of Alkenes with Bronsted Acids

• Mechanism: Similar to that of water addition with carbocations formed as intermediates.

Page 21: Alkynes Overview

• Definition: Hydrocarbons with triple bonds between sp hybridized carbons.

• Naming Convention: -yne suffix.

Page 22: Reactions of Alkynes

• Addition Reactions: Alkynes can undergo addition to halides and water.

• Markovnikov’s Rule: Applies in these reactions, similar to alkenes.

Page 23: Aldehydes and Ketones Structure

• Carbonyl Group: Characterizes aldehydes (terminal) and ketones (internal).

• Nomenclature: Aldehydes: -al; Ketone: -one.

Page 24: Carboxylic Acids and Amines Structure

• Carboxylic Acids: Identify structure with -COOH; replace –e with -oic.

• Amines: Derivatives of ammonia with classifications based on carbon attachment.