3.3.1.3 Isomerism Flashcards
What is isomerism?
When 2 or more compounds have the same molecular formula but differ in some other way
What is structural isomerism?
Same molecular formula, but different structural, displayed or skeletal formula
What is stereoisomerism?
Compounds/molecules with the same structural formula but with different atoms/bonds/groups arranged differently in space
What are the 3 types of structural isomers?
Chain isomers
Positional isomers
Functional group isomers
What is chain isomerism?
When there is more than one way of arranging atoms in the longest chain
What are the properties of chain isomerism?
Straight chains can pack closer together, so stronger Van der Waal forces, so higher m.p./b.p..
Branched chains cannot pack as close together so less surface area in contact, so weaker Van der Waal forces so lower m.p./b.p.
What is positional isomerism?
Positional isomers have the same carbon chain and the same functional group, but it is attached at different points along the carbon chain.
What is functional group isomerism?
Same molecular formula, but different functional group
What are the functional group isomer pairs?
Alkenes and cycloalkAnes
Aldehydes and ketones
Carboxylic acids and esters
What are the two types of stereoisomers?
E-Z Isomers
Optical isomers (a-level)
Why do E-Z isomers exist?
The double bond causes restricted rotation, so molecules cannot change structure, as this would require energy to break the double bond, which is not available at room temperature.
What are the Cahn-Ingold-Prelog (CIP) rules?
The higher the atomic number bonded to the carbons in the double bond, the higher the ranking. Priority groups are on the same side = Z isomer, opposite sides = E isomer
