1. The World of Organic Molecules
Symmetry
The World of Organic Molecules

2. What is Symmetry?

3. Symmetry is likeness of shape or arrangement about a center.

4. Does this Design Have Symmetry?

5. Symmetry About a Plane
Anything that contains an internal mirror plane is symmetric.
Anything that lacks an internal mirror plane is asymmetric.

6. Chirality
Asymmetric objects have an interesting property called Chirality which means “handedness”.
Chiral objects can have two different forms, a right-handed and left-handed form which are mirror images of each other but are not exactly alike.

7. Examples of Chiral Objects
Your Hands and Feet
Gloves and Shoes
Golf Clubs
Computer keyboard

8. Are the Following Objects Chiral or Achiral?
Baseball Bat
Refrigerator
Car
Bicycle
Your Face
Fork
Nail
Screw

9. Chiral Molecules?
A carbon atom with four different groups bonded to it creates a stereocenter in the molecule.
Most molecules which contain one or more stereocenters lack an internal plane of symmetry and are therefore chiral.

10. Enantiomers
The right-handed and left-handed forms of a chiral molecule make up a pair of stereoisomers called enantiomers.
Enantiomers are not identical, but they have the same physical properties such as melting point boiling point, etc.
So why do we care about this subtle form of stereoisomerism?

11. Chirality in the Biological World
When chiral organic compounds interact with living systems, the two enantiomers often interact very differently.
This is because living systems are chiral at many different levels in many ways:
- our hands and feet are chiral (of course)
- our taste buds are chiral
- our olfactory sensors are chiral
- our enzymes are chiral

12. Carvone

13. Carvone

14. Limonene

15. Limonene

16. Aspartame

17. Aspartame

18. Ibuprofen

19. Ibuprofen

20. Summary Molecules which lack symmetry are Chiral
Chiral molecules have right-handed and left-handed forms
Right-handed and left-handed molecules interact with living systems in very different ways.
Different smell
Different taste
Different drug effects