1. 1.Structural 2.Stereo isomers - geometric - optical

2. Starter:
Draw the 2 possible products formed when HCl is added to 2-methylbut-2-ene. Name the products and identify which is the major product. (Markovnikov’s rule)
Which type of reaction is this? addition, elimination or substitution

3. Difference between Molecular formula, structural formula and condensed structural formula.
Molecular formula: shows the atomic composition of the compound. E.g. Hexane = C6H14
(Compounds with the same molecular formulae can have different structures.)
2. Structural formula: shows the structure of the compound.
3. Condensed structural formula: shows structure in a more compact manner.
Hexane = CH3CH2CH2CH2CH2CH3

4. Summary Isomerism Stereoisomerism
Differences in spatial arrangement or groups caused by molecular asymmetry
Optical isomers
Left and right hand forms of 3-methyl hexane
Difference in spatial arrangement, or restriction due to double bond
Cis-trans isomers
Cis but-2-ene
And
Trans But-2-ene
Structural Isomerism
Different functional groups or combinations
Propanol
Propanone
Differences in position of functional groups
Propan-1-ol
Propan-2-ol
Differences in shape due to chain branching and ring formation
Pentane
and
2-methylbtane

5. Structural isomers Sometimes called constitutional isomers
Same molecular formula but a different arrangement of atoms (structure)
Can have different physical and chemical properties.

6. Structural isomers

7. Stereoisomers
Atoms arranged in same order but different position in space
There are two types
Geometric
Optical

8. Geometric or cis-trans isomers
Are caused by the rigidity of the double bond
Cis isomers same groups on the same side
Trans isomers have same groups on different sides
They have the same chemical properties but their physical properties differ

9. Geometric or cis-trans isomers

10. Optical Isomers A form of stereoisomerism
In stereoisomerism, the atoms making up the isomers are joined up in the same order, but still manage to have a different spatial arrangement.
Why optical isomers?
Optical isomers are named like this because of their effect on plane polarised light.
Simple substances which show optical isomerism exist as two isomers known as enantiomers.

11. Butan-2-ol

12. enantiomers.
A solution of one enantiomer rotates the plane of polarisation in a clockwise direction. This enantiomer is known as the (+) form.
A solution of the other enantiomer rotates the plane of polarisation in an anti-clockwise direction. This enantiomer is known as the (-) form. So the other enantiomer of alanine is known as or (-)alanine.

13. racemic mixture
When optically active substances are made in the lab, they often occur as a 50/50 mixture of the two enantiomers. This is known as a racemic mixture or racemate.
It has no effect on plane polarised light.

14. The examples of organic optical isomers required at this level all contain a carbon atom joined to four different groups. These two models each have the same groups joined to the central carbon atom, but still manage to be different:
Obviously as they are drawn, the orange and blue groups aren't aligned the same way.
Could you get them to align by rotating one of the molecules?

15. The next diagram shows what happens if you rotate molecule B.
They still aren't the same - and there is no way that you can rotate them so that they look exactly the same. These are isomers of each other.
non-superimposable
You only get optical isomers if all four groups attached to the central carbon are different.

16. One of the enantiomers is simply a non-superimposable mirror image of the other one.
In other words, if one isomer looked in a mirror, what it would see is the other one.
The two isomers (the original one and its mirror image) have a different spatial arrangement, and so can't be superimposed on each other.

17. Chiral and achiral molecules
A molecule which has no plane of symmetry is described as chiral.
The carbon atom with the four different groups attached which causes this lack of symmetry is described as a chiral centre or as an asymmetric carbon atom.
Only chiral molecules have optical isomers.

18. Butan-2-ol

19. Summary Isomerism Stereoisomerism
Differences in spatial arrangement or groups caused by molecular asymmetry
Optical isomers
Left and right hand forms of 3-methyl hexane
Difference in spatial arrangement, or restriction due to double bond
Cis-trans isomers
Cis but-2-ene
And
Trans But-2-ene
Structural Isomerism
Different functional groups or combinations
Propanol
Propanone
Differences in position of functional groups
Propan-1-ol
Propan-2-ol
Differences in shape due to chain branching and ring formation
Pentane
and
2-methylbtane

20. Key words Structural isomers Stereo isomers Cis and trans isomers
Optical isomers or enantiomers
Asymmetric carbon
Chiral
racemic

21. Key words Structural isomers- same MF different structure
Stereo isomers- same structural different spatial arrangement
Cis and trans isomers - due to double bond
Optical isomers or enantiomers- 4 different groups attached to a C
Asymmetric carbon- c with 4 different groups attached
Chiral - able to exist as non-super-imposable mirror image
Racemic – equimolar mixture of 2 optical isomers

22. Ibuprofen

24. Optical isomers
Caused when a carbon has 4 different groups attached to it
often called the chiral molecule or centre, also an asymmetric carbon
The 4 groups can attach in 2 different way so they are mirror images but can not be superimposed
These 2 optical isomers are called enantiomers

25. Optical isomers

26. Optical isomers

27. Optical isomers
Or draw one structural molecule, then draw a plane mirror and copy the exact mirror image of the first molecule.

28. Optical isomers
Try to draw the two optical isomers of butan-2-ol