14.6 Stereoisomerism Flashcards
What are stereoisomers
These are compounds whose molecules have the same atoms bonded to each other in the same way but with different arrangement of atoms in space so that molecules cannot be superimposed on each other
What are the two types of stereisomerism
1.geometrical(cis/trans) isomerism
2. Optical isomerism
What is one of the differences between C-C bond and C=C bond
There is no free rotation about C=C bond because of the presence of a pi bond
What is geometrical isomerism
Displayed by unsaturated or ring compounds with the same molecular formula and order of atoms but different shapes.
What is added in front of the name of geometrical isomer of a molecule
Cis and Trans
Why do the two stereoisomers with geometrical isomerism gave different physical properties
Because they have different arrangements of atoms in space so they are different compounds
Stereoisomers in geometrical isometric can also have different chemical properties such as
Different rates if reactions
Why is geometrical isomerism also possible in substituted cyclic compounds
Because of the limited rotation about C-C atoms that make up the rings
Why is geometrical isomerism also possible in substituted cyclic compounds
Because of the limited rotation about C-C atoms that make up the rings
We usually show cis and trans atoms using
A combination of skeletal and 3d formulae
What is optical isomerism
If a molecule that contains a carbon atom that is bonded to four different atoms or groups of atoms can form two optical isomers
What is the carbon atom with four different atoms or groups of atoms attached called. What is it referred as?
Chiral centre; ‘assymetric)
The two different optical isomers are called
Enantiomers
What are enantiomers
A pair of optically active molecules whose mirror image cannot be superimposed
Normal light is unpolarised, what does this mean
It can be thought of as fluctuating magnetic or electric field, vibrating at right angles to each other in every direction possible.
How is polarized light formed
By passing the unpolarised light through a polariser
What is the feature of polarised light
It vibrates in only one plane
What effect does a pair of optical isomers have on polarised light
A pair of optical isomers will rotate the pair of polarised light in equal amounts but in opposite directions. (Clockwise and anti-clockwise)
If an organic molecule has two chiral centres
Then there are four possible optical isomers
Substituted cyclic molecules can also have
Chiral centres
Why do symmetrical substituted cyclic molecules will not have a chiral centre
Starting from carbon atom bonded to the group substituted into the ring or bonded to the group, you will find two identical groups going around the ring in both clockwise and anti-clockwise direction. Therefore no carbon atom has four different groups attached to it.
