1. handedness in Molecules
7.4 CHIRALITY:
handedness in Molecules
Many molecules exist in “right-handed” and “left-handed forms

2. Mirror Images

3. A MIRROR IMAGE IS A REFLECTION

4. Your left hand is a “mirror image” of your right hand

5. Some mirror images are
‘superimposable’

6. Some mirror images are
not superimposable (‘nonsuperimposable’)
Nonsuperimposable mirror images have ‘right –handed’ and ‘left-handed’ forms… stereoisomers.

7. Molecules have mirror images too.

8. ‘kye-rality’ like reality
Chirality
Pronounced
‘kye-rality’ like reality

9. IN A MOLECULE… a “chiral center”
A carbon that is tetrahedral (sp3) and has four
different groups attached is called...
a “chiral center”

10. Another name is ….
stereocenter H F Cl Br

11. A molecule with one stereocenter
is ‘chiral’. B r F H C l

12. It’s mirror images are not superimposableF H C l C l H B r F
rotate H F B r C l
this molecule
is chiral
non-superimposable
mirror images
note that the fluorine
and bromine are
interchanged in the
mirror image
do interchanges in class

13. Practice with models Make a molecule with a stereocenter
Make it’s mirror image
Try to superimpose them
Are they the same or different molecules?
Interchange two of the atoms.
Now try to superimpose them.

14. PLANES OF SYMMETRY

15. A SYMMETRIC OBJECT HAS A PLANE OF SYMMETRY
- ALSO CALLED A MIRROR PLANE
plane of
symmetry
mirror
plane

16. IF AN OBJECT HAS A PLANE OF SYMMETRY,
ITS MIRROR IMAGE WILL BE IDENTICAL

17. IDENTICAL MIRROR IMAGES WILL SUPERIMPOSE
(MATCH EXACTLY WHEN PLACED ON TOP OF EACH OTHER)
IF AN OBJECT HAS AN IDENTICAL MIRROR IMAGE
IT’S………. ‘ACHIRAL’

18. CHIRAL An object without symmetry is no symmetry The mirror image
of a chiral object is
different and will not
superimpose on the
original object.

19. WHICH OBJECTS ARE SYMMETRIC ? WHICH OBJECTS ARE ACHIRAL ?
(mirror image is identical)
sym (outside)
achiral
achiral
sym
achiral
sym
achiral
sym

20. F F C l C l B r B r C l C l ACHIRAL TWO IDENTICAL GROUPS RENDERS A
The plane of the paper
is a plane of symmetry F F C l C l B r B r C l C l
TWO IDENTICAL GROUPS RENDERS A
TETRAHEDRAL CARBON ACHIRAL

21. F F C l C l B r C l B r C l TWO VIEWS OF THE PLANE OF SYMMETRY
side
view
edge
view

22. ACHIRAL A CARBON ATOM WITH THREE SIMILAR GROUPS IS ALSO ACHIRAL ….. ClBr

23. plane of
symmetry C l C l C l C l B r C l B r C l
side view
edge view

24. The whole secret of the study of nature lies in
learning how to use ones eye.
George Sand, author