Topic 4: Introductory Organic Chemistry and Alkanes

Topic 4: Introductory Organic Chemistry & Alkanes

4A: Introduction to Organic Chemistry (4.1 - 4.8)

4.1 - 4.3: Safety & Risk Assessment

In the lab, a hazard is the potential for a substance to cause harm, while risk is the likelihood of that harm occurring. Risk can be reduced by:

• Working on a smaller scale.
• Taking specific precautions (e.g., using a fume cupboard).
• Using less hazardous alternative substances.

4.4 - 4.5: Classification & Nomenclature

A homologous series is a family of compounds with the same general formula and functional group. You must be able to name compounds up to ${\text{C}}_{10}$ using IUPAC rules.

4.6 - 4.8: Reaction Types & Mechanisms

Reactions are classified as addition, substitution, oxidation, reduction, or polymerisation.

Bond Breaking:

• Homolytic Fission: The shared pair of electrons is split equally, producing free radicals.
• Heterolytic Fission: Both electrons from the bond go to one atom, producing ions.

4B: Alkanes (4.9 - 4.18)

Alkanes are saturated hydrocarbons with the general formula ${\text{C}}_n{\text{H}}_{2n+2}$.

4.10 - 4.12: Isomerism & Industrial Processing

Structural isomerism: Compounds with the same molecular formula but different structural arrangements.

Alkanes are obtained from crude oil via fractional distillation and then processed through cracking and reforming to produce more useful fuels.

4.13 - 4.16: Pollutants & Sustainability

Pollutant	Source/Effect
Carbon Monoxide	Incomplete combustion; toxic.
Oxides of Nitrogen/Sulfur	Contribute to acid rain.
Particulates (Soot)	Respiratory issues and global dimming.

The concept of carbon neutrality is applied to alternative fuels like bioethanol to reduce climate change impact.

4.18: Free Radical Substitution Mechanism

Alkanes react with halogens in the presence of UV light.

$$\text{Initiation: }{\text{Cl}}_2\stackrel{\text{UV}}{\to }2{\text{Cl}}^{·}$$
$$\text{Propagation 1: }{\text{CH}}_4+{\text{Cl}}^{·}\to {{\text{CH}}_3}^{·}+\text{HCl}$$
$$\text{Propagation 2: }{{\text{CH}}_3}^{·}+{\text{Cl}}_2\to {\text{CH}}_3\text{Cl}+{\text{Cl}}^{·}$$

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Exam Practice

Q1: Identify the type of bond breaking that occurs during the initiation step of free radical substitution.

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Homolytic Fission. The bond in the halogen molecule breaks evenly, with each atom receiving one electron from the shared pair to form two radicals.

Q2: Explain why carbon monoxide is a dangerous pollutant produced from the combustion of alkanes.

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It is produced by incomplete combustion and is highly toxic because it binds to hemoglobin in the blood, reducing its capacity to carry oxygen.