isomers

2 broad types of isomers

structural and stereo

3 types of structural isomers

chain, position and functional group

2 types of stereoisomers

configurational and conformational

what are configurational isomers

stereoisomers which cannot interconvert

what are conformational isomers

spatial arrangements of molecules through rotation of bonds

types of configurational isomers

geometric and optical

what is a stereogenic centre

a tetrahedral atom with four different substituents is called a stereogenic or chiral centre

what are enantiomers

show for this molecule

structures that are not identical and non-superimposable mirror images of each other

how to distinguish between enantiomers

both mirror images rotate plane polarised light in equal but opposite directions

other physical and chemical properties are the same

chirality of amines

can be chiral but are not configurationally stable - inversion of the lone pair is fast at room temperature

chirality of phosphines and sulfoxides + compare to amines

invert slower than amines so can be isolated as single enantiomers

what is planar chirality

features a planar system with a perpendicular substituent

flat ring above and below, Fe bond goes into middle of both rings - rings can spin around on metal axis

the bottom ring is symmetrical but the top ring is not

what is axial chirality

a non-planar arrangement of four groups about an axis

what is atropisomerism

restricted rotation around a chiral axis

as it rotates, the groups hit each other as they are big and bulky resulting in a steric clash

what are diastereomers

what are the types

differences between diastereomers?

stereoisomers with different configurations at one of more stereocentre

syn - groups on the same face

anti - groups on the opposite face

diastereomers have different physical and chemical properties and can be thought of as different compounds

number of possible stereoisomers and diasteromers for a compound with n stereocentres?

number of stereocentres?

show the diastereomers and label the syn and anti and any other types of isomerism exhibited

1,2 and 3,4 are pairs of enantiomers

the rest are all diastereomers to each other

number of stereocentres?

show the stereoisomers

what are meso isomers

explain with the example of this molecule

the stereoisomers have identical substituents but one diastereomer (not really?) is achiral due to a plane of symmetry/point of inversion - so this is a meso isomer instead as an achiral molecule cannot be a diastereomer

what are olefins

alkenes

geometric isomerism in olefins

olefins with non-identical substituents at both carbon atoms can exist as one of two geometrical isomers

nomenclature for 1,2-disubstitued olefins and for more substituted olefins

cis and trans for 1,2-disubstitued

E and Z for more substituted

how are geometric isomers of olefins named

Cahn-Ingold Prelog rule (for E&Z)

1. assign which end of the double bond is the highest in priority (this will have 1&2, while the other end will get 1’&2’)

2. on each carbon of the double bond, assign the priorities of each group

E: two higher priority groups on opposite sides

Z: two higher priority groups on the same side

name the isomers

types of geometric isomers for chiral molecules

how can they be determined

R and S

use Cahn-Ingold Prelog rule again

how to establish priority of substituents for chiral molecules

1. an element of higher atomic number has priority over an element of lower atomic number (e.g. O > N > C > D > H > lone pair)

2. a greater number of higher priority atoms takes precedence over a lesser number (e.g. -CHCl2 > CH2Cl)

3. multiple bonds are regarded as representing two (or three) bonds to the atom of that mass

4. if steps 1-3 fail to distinguish any substituents, move to the next atom in the ring or chain and repeat. continue this cycle until all substituents are distinguished

steps in Cahn-Ingold Prelog rule to determine R and S

1. prioritise the substituents on the molecule from 1 (highest) to 4 (lowest)

2. redraw the molecule to lok down the bond of lowest priority

3. determine if substituents 1, 2 and 3 are in a clockwise of anticlockwise order

R: substituents are clockwise

S: substituents are anticlockwise