Groups and isomers

• Empirical formula shows the simplest whole number ratio of atoms of each element in a compound.
• Molecular formula shows the true number of atoms of each element in a compound.
• Structural formula shows the arrangements of atoms in a compound.
• Displayed formula shows every bond between atoms in a compound.
• Skeletal formula shows the bonds and any non carbon atoms in a compound
• Homologous series have the same functional group and differ by CH2.
• Reaction mechanics show the movement of electrons within a reaction, represented by curly arrows.
• Isomers have the same molecular formula but a different arrangement of atoms.
• Structural isomers have different structural formulas ie can be straight or branched chains.
• Position isomers have the functional group of the molecule in a different position on the carbon chain.
• Functional groups are specific arrangements of atoms that give compounds specific properties.
• Functional group isomers have different arrangement of atoms so that the molecule has a different functional group.
• Stereoisomers have a different arrangement in space.
• E-Z stereoisomers are due to limited rotation around a carbon double bond where the E isomer has priority groups across diagonally and the Z isomer has priority groups on the same side.
• Cahn-Ingold-Prelog (CIP) priority rules say that groups with a higher Mr have a higher priority in E-Z isomerism.
• Optical isomerism is a type of stereoisomerism where molecules have the same molecular formula but a different spatial arrangement.
• Optical isomerism occurs with a chiral centre, where a carbon atom has four different groups bonded to it.
• The presence of a chiral centre leads to two possible isomers called enantiomers that are mirror images of each other and rotate plane polarised light by 90 degrees in opposite directions.
• A racemate, or racemic mixture, is formed when there are equal amounts of a pair of enantiomers and is optically inactive.