Hydrocarbons and Isomerism

Similarities and Difference Between Alkenes and Cycloalkanes

Both have the same molecular formula. Alkenes have at least one double bond in their structure while cycloalkanes have only single bonds.

Another name for Alkanes

Paraffin

Chemical Property of Alkanes

1. Least reactivity and the chemical process is mainly combustion

2. Reacts with oxygen to produce heat, carbon dioxide and water (combustion reaction)

3. They undergo substitution reaction

Substitution reaction

Reaction in which an atom is replaced with another

Addition reaction

Reaction in which an atom is added to the molecule

Chemical Reactions of Alkenes nd Alkynes

• Hydrogenation

• Halogenation

• Hydrohalogenation

• Hydration

Physical properties of Hydrocarbons

1. they are non polar

2. they are odourless and colourless

3. Their boiling and melting points increases with increasing molecular weight

Factor that affect boiling melting points of hydrocarbons

The branching in organic compounds reduces the melting and boiling point.

Least dense Hydrocarbon

Alkane

Isomerism

The concept where compounds with different structures have the same molecular formula

Types of Isomerism

1. Constitutional/ structural Isomerism

2. Stereoisomerism

Constitutional/ Structural Isomers

1. These compounds have the same molecular formula but different atomic arrangements

2. They have different IUPAC names

3. The compounds may have the same or different functional groups

4. They have different chemical and physical properties

Some types of Constitutional Isomerism

1. Positional Isomerism

2. Functional Isomerism

3. Chain or skeletal Isomerism

Positional Isomerism

These are the isomers with the same functional groups but at different positions in the molecular structure

Functional group isomerism

these are the isomers with different functional groups

Chain or skeletal isomerism

These are isomers that have the same functional groups, molecular formula but different carbon structures

Stereoisomerism

This refers to compounds that have the same molecular formula and connectivity but have different arrangements of atoms in three dimensional space

Types of Stereoisomerism

1. Conformational Isomerism

2. Optical Isomerism

3. Geometric Isomerism

Conformational isomerism

This type of isomerism arises due to the rotation of a single carbon-carbon bond

Types of Conformational Isomerism

staggered conformation, eclipsed conformation

Staggered conformational Isomerism

This is the most stable type of conformation

Anti Staggered conformational Isomerism

In this staggered conformation bulky groups such as methyl and halogens are placed 180 degrees apart from each other.

Gauche staggered conformation

In this staggered conformation bulky groups such as methyl and halogens are placed 60 degrees apart from each other.

Eclipse conformation

this is the least stable conformation isomerism

Geometric Isomerism

This is the type of isomerism where the order of atom bonds in the isomers are the same but different in a three dimensional plane

Cis Isomer

polar molecules of the same atoms that are on the same side of double bonds.

Trans isomer

a non polar isomer in which the functional groups are located on the other sides of the double bond

Optical Isomerism

This is the type of isomerism where two stereoisomers are related to each other by a reflection

Enantiomers

Two compounds with the exact same connectivity, that are mirror images of each other but that are not identical to each other

Diastereomers

wo molecules which are stereoisomers (same molecular formula, same connectivity, different arrangement of atoms in space) but are not enantiomers