3.7 Organic naming and isomerism

Faduma Omar
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Faduma Omar
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3.7 Organic naming and isomerism
1 Definitions
1.1 Hydrocarbon : compound that only consists of H and C
1.1.1 Saturated : Contains carbon carbon single bonds only Unsaturated : Contains atlas 1 carbon carbon double bond Molecular formula : Formula which shows actual number of each type of atom Empirical : shows simplest whole number ratio of atoms of each element in the compound General formula : algerbaric formula for a homologous series i.e Cnh2n Displayed formula : shows all covalent bonds present in a molecule functional group : an atom or group of atoms which when present in different molecules causes them to have similar chemical properties homologous series : are family of organic compounds with same functional group and same general formula. They show a gradual change in physical properties and have the same chemical properties. Each member differs by ch2 from the last.
2 Drawing displayed formula:
2.1 The carbon always has 4 bonds, since the shape around the carbon atom is tetrahedral (bond angle 109.5)
3 Naming carbon chains
3.1 1) count longest carbon chain
3.1.1 2) Find any branched chains and count how many carbons they contain and thus had the appropriate prefix for the alkyl groups
3.1.2 Suffix for carbon length
3.2 Order of precedence for prefix/suffix:
3.2.1 double/triple bonds c-c bonds always take suffix form Carboxylic acids> carboxylic acid derivatives> nitriles> aldehydes> ketones>alcohols> amines
3.2.2 highest precedence groups always take suffix form whilst others take prefix form
3.3 general rules: 1) if the suffix starts with a vowel remove the E i.e e from alkane name or propan-1-ol
3.3.1 2) if suffix starts with a consonant or there are 2 or more functional groups (di,tri...) do not remove E i.e propanenitrile, ethane-1,2-diol 3) position of functional group is given by which carbon it is on, the functional group always wants the lowest number. For aldehydes, cA and nitriles, the functional group number is always 1. 4) functional groups tale precedence over branched chains in giving the lowest number
4 isomers
4.1 Structural isomers: same molecular formula but different structural formulae.
4.1.1 Structural isomerism can arise from, 1)chain isomerism 2) position isomerism and 3) functional group isomerism Chain isomers: compounds with same molecular formula but different structures of the carbon skeleton position isomers : compounds with same molecular formula but different positions of the functional group on the same carbon skeleton functional group isomers: compounds with same molecular formula but with atoms arranged into different functional groups.
4.2 stereoisomerism
4.2.1 stereoisomers have same structural formulae but different spacial arrangement of atoms there are 2 types of stereoisomerism: 1) e/z stereoisomerism and 2) optical isomerism alkenes can exhibit e/z isomerism. E/z isomerism exists due to restricted rotation about the c=c bond. single c-c bonds can rotate easily. e/z isomerism arise when: there is restricted rotation around c-c bond and when there are 2 or more different groups/atoms attached to both end of the restricted double bond. They are e/z stereo isomers because the 2 isomers cannot be switched to each other. naming e/z isomers: - both sides of double determine the priority groups. The atoms with the bigger Ar is classed as the priority groups, if these are on the same side, they are known as Z isomers, however if they are on the opposite sides of the double bond, then they are considered E isomers. optical isomers: occcur in carbon compounds with 4 different groups of atoms attached to a single carbon (chiral carbon or asymmetric carbon). These four groups are arranged tetrahedrally around the carbon. This causes 2 different isomers that are not superimposable to be formed which are mirror images. Two compounds that are optical isomers are called enantiomers. They have the similar chemical/physical properties but they rotate plane polarised light in different directions A mixture containing 50;50 of both enantiomers is called a racemic mixture. a racemate will not rotate plane polarised light since both enantiomers rotate plane polarised light in different directions by equal amounts.
5 chemical reactions and optical isomers:
5.1 Formation of a racemate
5.1.1 racemate will form when a trigonal planar carbonyl group is approached from both sides by the hen attacking species. this results in formation of racemic mixture. there is equal amount of both enantiomer forming . no optical activity is seen.
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