10 Organic Chemistry

This enables it to form long chains of carbon atoms, and hence an almost infinite variety of carbon compounds are known The tendency of identical atoms to form covalent bonds with each other and hence form chains is known as catenation

Carbon always forms four covalent bonds which can be single, double or triple bonds

A functional group is a specific atom or group of atoms which confer certain physical and chemical properties onto the molecule Organic molecules are classified by the dominant functional group on the molecule

Organic compounds with the same functional group, but a different number of carbon atoms, are said to belong to the same homologous series Every time a carbon atom is added to the chain, two hydrogen atoms are also added

Things we can say about a homologous series: - each member has the same functional group - each member has the same general formula - each member has similar chemical properties - each member differs by -CH2 - - members have gradually changing physical properties, for example, boiling point, melting point and density

As a homologous series is ascended, the size of the molecule increases This has an effect on the physical properties, such as boiling point and density

increasing linearly with plateau

The broad trend is that boiling point increases with increased molecular size Each additional -CH2 - (called the homologous increment ) adds 8 more electrons to the molecule This increases the strength of the London Dispersion Forces Stronger LDF leads to a higher boiling point These trends are followed in other homologous series

Empirical Formulae Molecular Formulae Structural Formulae Condensed Structural Formulae

The empirical formula shows the simplest possible ratio of the atoms in a molecule

The molecular formula shows the actual number of atoms in a molecule e.g. C4H10

The structural formula shows the spatial arrangement of all the atoms and bonds in a molecule This is also known as the displayed formula or graphical formula. full drawing of molecule

In a condensed structural formulae enough information is shown to make the structure clear, but most of the actual covalent bonds are omitted

Only important bonds are always shown, such as double and triple bonds Identical groups can be bracketed together Side groups are also shown using brackets Straight chain alkanes are shown as follows:

Structural isomers are compounds that have the same molecular formula but different structural formulae Eg. propene and cyclopropane

There are three different types of structural isomerism: Branch-Chain isomerism Positional isomerism Functional group isomerism

Branch-Chain isomerism is when compounds have the same molecular formula, but their longest hydrocarbon chain is not the same This is caused by branching Eg. pentane and 2,2-dimethylpropane

Positional isomers arise from differences in the position of a functional group in each isomer The functional group can be located on different carbons For example, butan-1-ol and butan-2-ol

When different functional groups result in the same molecular formula, functional group isomers arise The isomers have very different chemical properties as they have different functional groups For example, butanol and ethoxyethane

Saturated hydrocarbons are hydrocarbons which contain single bonds only resulting in the maximum number of hydrogen atoms in the molecule

Unsaturated hydrocarbons are hydrocarbons which contain carbon-carbon double or triple bonds

Hydrocarbons are compounds containing hydrogen and carbon only

There are four families of hydrocarbons you should know: alkanes, alkenes, alkynes and arenes

Alkanes have the general molecular formula CnH2n+2. They contain only single bonds and are said to be saturated