SS2 Third Term Chemistry Lesson Note – Hydrocarbons II

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WEEK 8

TOPIC: HYDROCARBONS

CONTENTS:

1. Isomerism-structural and geometric
2. Alkene-IUPAC nomenclature, method of preparation, properties and uses
3. Alkyne- IUPAC nomenclature, method of preparation, properties and uses
4. Aromatic hydrocarbon: benzene-properties and uses

ISOMERISM

Definition: Isomerism is the existence of two or more compounds (known as isomers) with the same molecular formulae but different molecular structures

ISOMERISM IN ALKANES

Structural isomerism in alkanes is obtained by branching the straight chain isomer.

(a)   Draw the isomers of the compound with molecular formula

(i) C₄H₁₀ 

CH₃CH₂CH₂CH₃ (butane); CH₃CH(CH₃)CH₃ 2-methylpropane

(ii) C₅H₁₂   CH₃CH₂CH₂CH₂CH₃ Pentane     CH₃CH(CH₃)CH₂CH₂ 2-methylbutane    CH₃CH(CH₃)₂CH₃ 2,2-dimethypropane

GEOMETRIC ISOMERISM

This is the existence of of organic compounds with the same molecular formula but different spatial arrangement of compound atoms. Geometric isomers have similar chemical properties but different physical properties. We have the cis-isomers and trans-isomers. Geometric isomerism is common in alkenes.

ALKENES

The alkenes are the homologous series with the general molecular formula CnH₂n; n starts from 2. They are unsaturated hydrocarbons due to the double bond in their structures.

ISOMERISM IN ALKENES

1. Isomers of C₄H₈

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