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Home , Homologous series

2014/01/01

ORGANIC COMPOUNDS GROUPS OF ORGANIC Can be COMPOUNDS - COMPOUNDS of CARBON Introduction to and HYDROGEN only. Can be either AROMATIC ALIPHATIC HYDROCARBONS – HYDROCARBONS – straight chain structures which have benzene ring structures – with double bonds ALKANES – single bonds – double bonds – triple bonds

Some terminology: Saturated hydrocarbons – these molecules have only single bonds between carbon atoms e.g. alkanes. Unsaturated hydrocarbons Those compounds with a double or triple bonds between carbon atoms are said to be unsaturated – since they do not have the maximum number of H atoms per number of C atoms. e.g. Alkenes & – single Ethene – double Ethyne – triple alkynes: bond between bond between bond between Test for unsaturated carbons carbons carbons compounds Naming alkanes

A homologous series is a family of compounds Hydrocarbons can be represented by: where each member differs from the previous

one by a CH2 group. Can be represented by a • a molecular formula C2H6 general formula. Homologous series Functional groups are small structural units • a condensed structural formula within molecules at which most of the chemical CH3CH3 reactions occur. The determines the chemical properties of the molecule. • a structural formula Ethanoic acid Carbon tetra- chloride Ethane

Ethanol

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ISOMERS Isomers of ALKANES Organic molecules having the same molecular formula but different structural formula, are called isomers. Isomers The carbon atoms are joined to each other by single bonds. Each C atom makes 4 covalent C5H12 has 3 isomers, i.e. different arrangement of atoms. bonds and so all other bonds are to hydrogen atoms. Isomer of

Each has 5 C & 12 H atoms. C H CH4 Ethane C2H6 3 8 The larger the molecule, the more the number of First 5 alkanes Equivalent structures for isomers. They have different properties. pentane

THE HOMOLOGOUS SERIES FOR YOU TO DO: Homologous series Alkane No Molecular Condensed structural formula of C Formula name Create a similar table for the alkenes. 1 Methane CH4 CH 4 Replace one of the C – C bonds with a 2 Ethane C2H6 CH CH 3 3 double C=C bond. Naming alkenes and alkynes Propane 3 C H 3 8 CH3CH2CH3 4 Butane C4H10 CH CH CH CH3 3 2 2 Create a similar table for the alkynes. 5 Pentane C5H12 CH CH CH CH CH 3 2 2 2 3 Replace one of the C – C bonds with a 6 Hexane C6H14 CH CH CH CH CH CH 3 2 2 2 2 3 triple C-C bond. Heptane 7 C H 7 16 CH3 CH2 CH2CH 2CH2CH2CH3 8 Octane C8H18 CH3 CH 2CH2 CH2CH 2CH2CH2CH3 Draw structural formulae for each molecule 9 CH CH CH CH CH CH CH CH CH Nonane C9H20 3 2 2 2 2 2 2 2 3 represented in the tables.

Decane 10 C 10H22 CH3CH2CH 2CH2CH 2CH2CH 2CH2CH2CH3

Straight and branched chain hydrocarbons: Distinguish between the hydrocarbons The hydrocarbons represented in the table using the general formulae General formulae & homologous series given in the previous slide are all STRAIGHT chain hydrocarbons. General Ethane Carbon chains can be branched, which Formula means that one of the hydrogen atoms is Ethene Alkane CnH2n replaced by an group. Ethyne 2 – methylbutane CnH2n +2

Alkyne CnH2n - 2

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Naming alkyl groups Naming alkyl groups FUNCTIONAL GROUPS Functional groups

Alkyl group Alkyl name structure

CH3 - methyl

CH3CH2- ethyl

CH3CH2CH2 - propyl

CH3CH2 CH2CH2 - butyl

Functional groups

RULES FOR NAMING ORGANIC COMPOUNDS (IUPAC RULES) 3. Number the carbon atoms in the chain. Number them so that the functional group 1. Identify the functional group of the molecule is on the carbon of lowest possible – this determines the ending of the name. number. Double and triple bonds take Eg – only single bonds – ends in -ane preference over side chains.

2. Find the longest continuous carbon chain 4. Name the branched group according to the and allocate its prefix according to the number of carbon atoms it has and give number of carbon atoms in the chain it a number according to the carbon atom (see table for prefixes). it is attached to. Nomenclature rules

Name prefixes (the part in front of the basic name) No of C Prefix 5. If there is more than one branched group of atoms the same kind, use the Greek prefixes di, 1 meth tri, tetra, penta and so on to indicate this. 2 eth - 3 prop - 6. If a halogen atom is attached to the carbon 4 but - Propane chain, it is treated as an alkyl group. 5 pent - 6 hex - The prefixes: fluoro-, chloro-, bromo -, and iodo 7 hept - – are used. 8 oct - eg tetra-chloro methane CCl4 9 non - Naming haloalkanes 10 dec - Hexane

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7. For , the name ending –ol is Other homologous series are treated in the same used. e.g . manner as for alcohols and halo alkanes.

It is important that you have practise at naming as many organic compounds as possible.

8. For carboxylic acids, the name ending Also try writing the structural formula – having been – oic acid is used. given the name of the organic compound. eg ethanoic acid. It will take a little while to get used to this naming system – with so many new words, prefixes and suffixes.

However, you can & will get it right.

Name these: Apply the rules:

IUPAC naming of compounds

Longest chain – 4 carbon atoms = prefix but Functional group – alkane = name ends -ane Alkyl group on C2 = 2-methyl ∴ name of compound is: 2-methyl butane

Draw the structural formula for these compounds:

1. Methyl propane

2. 3-methyl pentane

3. 2-methyl, 3-ethyl hexane

4. 2,3-dimethyl, 3,4,5-triethyl nonane

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