1. CONSTITUTIONAL ISOMERS ISOMERS ENANTIOMERS STEREOISOMERS DIASTEREOMERS
Different compounds
with the same
molecular formula
Isomers with a different
order of attachment of
the atoms in their
molecules
Each isomer could
have stereoisomers
ENANTIOMERS
Stereoisomers whose
molecules are non-
superimposible mirror
images of each other
DIASTEREOMERS
molecules are not mirror
STEREOISOMERS
Isomers with the same order
of attachment, but a different
configuration (3D arrangement)
of groups on one or more of
the atoms
double bond or ring
with a ring
cis/trans
ISOMERS
both can apply
(geometric)
TYPES OF ISOMERISM

2. Relationship of Constitutional and Stereoisomers

3. Relationships of Stereoisomers

4. FISCHER PROJECTIONS

5. في الكيمياء ( وخاصة الكيمياء العضوية والحيوية), يعنى مسقط فيشر تمثيل ثنائي الأبعاد للجزيء العضوي ثلاثي الأبعاد كمسقط. يتم رسم جميع الروابط كخطوط أفقية أو عمودية.
ويتم تمثيل سلسلة الكربون رأسيا, وتمثيل ذرات الكربون بمركز الخطوط المتقاطعة. كما يتم تمثيل ذرة الكربون الأولى C1 في الأعلى. وقد تم تقديم مسقط فيشر بواسطة إيميل فيشر.

7. فى مسقط فيشر, كل الروابط الأفقية يتم إسقاطها للأمام (كما لو كانت خارجة من الصفحة أو الشاشة). وعلى ذلك, لا يمكن تدوير مسقط فيشر (2n+1) × 90° في مستوى الصفحة أو الشاشة, حيث أن إتجاه الروابط متناسب لبعضه البعض ولذلك يتغير, محور الجزيء إلى مقابله الضوئي.

8. EVOLUTION OF THE FISCHER PROJECTION C H O O H H O C H C H O C H O H O
“Sawhorse” Projection
EVOLUTION OF THE
FISCHER PROJECTION C H O O H H O C 2 H
Fischer Projection
Orient the
main chain
vertically with
the most
oxidized group
at the top. C H O C H O H O H H O H C H 2 O C H O H 2
Substituents will
stick out toward
you like prongs
Main chain bends
away from you

9. OH H
ORIENTATION OF
THE MAIN CHAIN
AND THE
SUBSTITUENTS
IN A FISCHER
PROJECTION OH H H OH
continuation
of the main chain

10. H C l B r CH3 H Cl Br H CH3 3 rotate CH3 90o Cl H main chain in red H
orient main chain
vertically Br
CH3 H Cl Br
convert to
Fischer
Projection H
CH3

11. تحديد الهيئة الفراغية المطلقة ( R و S ) من خلال مسقط فيشر
DETERMINATION OF
R / S CONFIGURATION
IN FISCHER PROJECTIONS

12. CHO H H O H OHC C H O H C H O H O H R O H CHO R HOCH2 CHO H O H H C H
PLACE THE PRIORITY=4 GROUP IN ONE OF THE VERTICAL
POSITIONS, THEN LOOK AT THE OTHER THREE 2 4
#4 at top position
CHO H 1 H O H
OHC C H O H 4 2 2 3 C H O H O H R 2 3 1
alternatively:
BOTH IN BACK
SAME RESULT 1 2 O H
CHO R 3 2 1
HOCH2
CHO H O H 4 H C H O H 2 4 3
#4 at bottom position

13. FOR THE MENTALLY AGILE S R CHO H O H C H O H 2
WHY BOTHER INTERCHANGING?
JUST REVERSE YOUR RESULT!
Same molecule
as on previous
slide. 2 S
reverse R
CHO H O H 1
Same result
as before. 4 C H O H 2 3
H coming
toward you

14. * * * * * R R R S S R S S 22 = 4 stereoisomers R R R R S S R R S S R S

15. Drawing Enantiomers and Diastereomers Tutorial and Exercises
Link to:
Drawing Enantiomers and Diastereomers Tutorial and Exercises
Tutorials Topic List
Stereochemistry Practice Problems

16. Stereospecificity and
stereoselectivity

17. stereospecificity is the property of a chemical reaction that yields different stereoisomeric reaction products from two stereoisomeric reactants depending on the reaction conditions

18. stereoselectivity is the property of a chemical reaction that yields an unequal mixture of stereoisomers from a single reactant

19. مقارنــة بـين stereoselectivity
describes a reaction where the mechanism allows for the formation of both products, but the formation of one of the products is favored
Stereospecificity
describes a reaction that necessarily yields a given stereoisomer because of the mechanism of the reaction

20. yields an unequal mixture of stereoisomers from a single reactant.
مقارنة بين
stereoselectivity
yields an unequal mixture of stereoisomers from a single reactant.
Stereospecificity
yields different stereoisomeric reaction products from two stereoisomeric reactants depending on the reaction conditions

21. always yields 100% of a particular stereoisomer
مقارنة بين
stereoselectivity
may be partial, where the formation of one stereoisomer is favoured over the other, or it may be total where only one stereoisomer is formed
Stereospecificity
always yields 100% of a particular stereoisomer

22. For example, the addition of dibromocarbene to cis and trans-2-butene
مقارنة بين
stereoselectivity
An example of partial stereoselectivity is dehydrohalogenation of 2-iodo-butane which yields 80% trans-2-butene and 20% cis-2-butene
Stereospecificity
For example, the addition of dibromocarbene to cis and trans-2-butene

25. CONFIGURATION
ABSOLUTE CONFIGURATION ( R / S )

26. CONFIGURATION The three dimensional arrangement of the
groups attached to an atom
Stereoisomers differ in the configuration at one or
more of their atoms.

27. R S CONFIGURATION - relates to the three dimensional 1 2 2 1 C C 4 4 3
sense of attachment for groups attached to a chiral
atom or group of atoms (i.e., attached to a stereocenter). 1 2 2
counter
clockwise
clockwise 1 C C 4 4 3 3
view with
substituent
of lowest
priority in
back R S
(rectus)
(sinister)

28. SPECIFICATION OF CONFIGURATION
Enantiomers are assigned a CONFIGURATION
using the same priority rules we developed for
E/Z stereoisomers.
1. Higher atomic number has higher priority.
2. If priority cannot be decided based on the first
atom attached move to the next atom, following
the path having the highest prioity atom.
3. Expand multiple bonds by replicating the atoms
attached to each end of the bond.
CAHN-INGOLD-PRELOG
SEQUENCE RULE

29. Bromochlorofluoroiodomethane1 1 4 4 2 3 3 2 R S
Enantiomers

30. How Many Stereoisomers Are Possible?
maximum number of stereoisomers
= 2n,
where n = number of stereocenters
(sterogenic carbons)
sometimes fewer
than this number
will exist

31. IMPORTANCE OF STEREOCHEMISTRY
# AN ACHIRAL REAGENT REACTS IDENTICALLY WITH BOTH ENANTIOMERS.
# AN ACHIRAL SOCK FITS ON EITHER FOOT
# A CHIRAL REAGENT REACTS DIFFERENTLY WITH EACH ENANTIOMERS.
# A CHIRAL SHOE FITS ON ONLY ONE FOOT.

32. RECEPTORS ARE PROTEINS THAT BIND PARTICULAR MOLECULES.
BECAUSE A RECEPTOR WILL RECOGNISE ONLY ONE OF A PAIR OF ENANTIOMERS, ENANTIOMERS CAN HAVE DIFFERENT PHYSIOLOGICAL PROPERTIES.

33. RECEPTORS LOCATED ON THE EXTERIOR OF NERVE CELLS IN THE NOSE ARE ABLE TO PERCIEVE AND DIFFERENTIATE THE ESTIMATED SMELLS TO WHICH THEY ARE EXPOSED.

34. (R)-(-)-CARVONE IS FOUND IN SPEARMINT OIL AND (S)-(+)- CARVONE IS FOUND IN CARAWAY SEED OIL.
EACH HAS A DIFFERENT SMELL AS IT FITS INTO DIFFERENT RECEPTORS.

36. (S)-(-)-KETAMINE IS FOUR TIMES MORE POTENT THAN (R)-(-)-KETAMINE AND HAS LESS SIDE EFFECTS.
THE ACTIVE INGREDIENT OF IBUPROFEN IS THE (S)-(+)-ISOMER.

37. THE STEREOCHEMISTRY OF REACTIONS ARE VERY IMPORTANT.
A REGIOSELECTIVE REACTION FORMS MORE OF ONE CONSTITUTIONAL ISOMER THAN THE OTHER.
A B + C MORE ‘B’ IS FORMED THAN ‘C’, WHERE B AND C ARE CONSTITUTIONAL ISOMERS.

38. A STEREOSELECTIVE REACTION FORMS MORE OF ONE STEREOISOMER THAN THE OTHER.
A B + C MORE ‘B’ IS FORMED THAN ‘C’, WHERE B AND C ARE STEREOISOMERS.

39. ‘A’ AND ‘C’ ARE STEREOISOMERS ‘B’ AND ‘D’ ARE STEREOISOMERS
IN A STEREOSPECIFIC REACTION, EACH STEREOISOMERIC REACTANT FORMS A DIFFERENT STEREOISOMERIC PRODUCT OR A DIFFERENT SET OF STEREOISOMERIC PRODUCTS.
A B
C D
‘A’ AND ‘C’ ARE STEREOISOMERS
‘B’ AND ‘D’ ARE STEREOISOMERS
A STEREOSPECIFIC REACTION IS ALSO STEREOSELECTIVE. A STEREOSELECTIVE REACTION IS NOT NECESSARILY STEREOSPECIFIC

40. ALL THE REACTIONS THAT OCCUR IN BIOLOGICAL SYSTEMS ARE CATALYSED BY ENZYMES.
AN ENZYME CATALYSED REACTION FORMS ONLY ONE STEREOISOMER BECAUSE AN ENZYME POSSESSES A CHIRAL BINDING SITE.
THEY ARE COMPLETELY STEREOSELECTIVE.
THE ENZYME FUMARASE, WHICH CATALYSES THE ADDITION OF WATER TO FUMARATE, FORMS ONLY (S)-MALATE.

41. FUMARASE CATALYSE THE ADDITION OF WATER TO FUMARATE BUT NOT TO MALEATE
ENZYME CATALYSIS IS STEREOSPECIFIC. AN ENZYME CATALYSES THE REACTION OF ONLY ONE STEREOISOMER.
FUMARASE CATALYSE THE ADDITION OF WATER TO FUMARATE BUT NOT TO MALEATE
AN ENZYME CAN DIFFERENTIATE STEREOISOMERS BECAUSE OF THE CHIRAL BINDING SITE