Isomerism Flashcards
isomer definition
2 molecules that have the same molecular formula but differ in the way their atoms are arranged
what are the difference between isomers?
have different physical properties and sometimes different chemical properties
structural isomerism definition
-same molecular formula
- different structural formula
stereoisomerism definition
- same molecular formula
- same structural formula
- different spatial arrangements (geometries)
what are the three types of structural isomerism?
- chain
- position
- functional group
what are chain isomers?
type of structural isomerism.
carbon chains arranged differently - different carbon skeletons.
what are position isomers?
type of structural isomerism.
the functional group is attached to the main chain in a different location.
what are functional group isomers?
type of structural isomerism.
the atoms are reorganised to give a different functional group.
between what 4 pairs is functional group isomerism shown?
- alkenes and cycloalkanes
- aldehydes and ketones
- alcohols and ethers
- carboxylic acids and esters
what is the functional group for aldehydes?
what is the functional group for ketones?
what is the functional group for alcohols?
C—OH
what is the functional group for ethers?
C - O - C
what is the functional group for carboxylic acids?
what is the functional group for esters?
what is E/Z isomerism?
type of stereoisomerism that occurs due to the restricted rotation around the carbon double bond
_____ show E/Z Isomerism
alkenes
Explain how alkenes show E/Z isomerism
- Alkenes have restricted rotation around their C=C double bonds
- & if both of the double-bond carbons have 2 different functional groups attached to them = get 2 stereoisomers (E/Z isomerism)
why can’t alkanes and halogenoalkanes display E/Z isomerism?
free rotation around the single carbon bond- means that the molecule are still the same, just rotated
Where are the same groups situated in (cis) Z-isomer?
Either both above or both below double bond
(matching groups are on ‘ze zame zide’)
Where are the same groups situated in (trans) E-isomer?
Same groups positioned across the double bond
What rules do we use to identify whether a molcule with a C=C bond, surrounded by 3 or 4 different functional groups, is a E- or Z- isomer?
Use the Cahn-Ingold-Prelog (CIP) priority rules
Describe how we use the CIP rules to identify a E-/Z-isomer
Identify the groups directly bonded to each of the C=C carbon atoms
Assign a priority by finding the atom with the highest atomic number - this given the highest priority
If higher priority groups = same side of molecule = Z-isomer OR if higher priority groups = different sides of molecule = E-isomer
CIP rules: What do you do if the atoms directly bonded to carbon are the same?
Look at next heaviest atom in the groups to work out which has the higher priority
what is the polarity of an E-isomer?
polar bonds cancel each other out
what is the polarity of a Z-isomer?
more polar than E-isomers
