Isomerism Flashcards
structural isomer definition
same molecular formula, differnt structural formula
stereoisomerism
same structural formula, different arrangement of atoms in space
E/Z isomers
C=C restricts rotation, has two differnt groups attached
optical isomerism
form of stereoisomerism
non-superimposable mirror images
formed when a carbon atom bonds to four differnt groups
what is optical isomerism
they rotate the plane of polarized light- one isomer will rotate it clockwise, the other isomer will rotate it anti-clockwise
Chiral carbon definition
a molecule which can exist as a pair of optical isomers
chiral center or stereogenic centre or asymmetric definition
the carbon which is attached to 4 different groups
enantiomerically pure
a sample that contains only one optical isomer
optically active definition
enantiomerically pure compound is optically active as it rotates the plane of polarized light
racemic mixture
a mixture that contains equal quantities of enantiomers- not optically active
mechanism for the reduction of aldehydes to ketones
Reagent: NaBH4
Mechanism: Nucleophilic addition
Nucleophile: Hydride ion :H-
Condition: Acidic solvent
mechanism for the addition of hydrogen cyanide to aldehydes and ketones
reagent: KCN then HCl
Mechanism: Nucleophilic addition
Condition: Acidic solvent needed
Name of product: hydroxy nitrile
HCN is a weak acid so why can’t we use it as a source of the nucleophile
partially dissociates into H+ and -CN so low conc of [-CN]
why can nucleophilic addition to aldehydes and asymmetrical ketones result in a racemic mixture of optical isomers
the bonding about a carbonyl group in an aldehyde and ketone is planar. this means there is a 50 50 chance of the nucleophile attacking from one side of the molecule to the other
this results in equal proportions of each optical isomer forming and so a racemic mixture is formed
