1. Chapter 5: Stereochemistry
The three-dimensional structure of a molecule can greatly affect its physical and chemical properties. Can you give some examples?
Three dimensional structure is critical in biochemistry. HOW?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

2. Chapter 5: Stereochemistry
For pharmaceuticals, slight differences in 3D spatial arrangement can make the difference between targeted treatment and undesired side-effects. WHY?
Isomers that have the same connectivity between atoms but different 3D, spatial arrangement of their atoms are called STEREOisomers
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

3. Klein, Organic Chemistry 2e
5.1 Isomers
Isomers are NONidentical molecules that have the same formula
There are two classifications of isomers
Draw a pair of molecules that are constitutional isomers
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

4. Klein, Organic Chemistry 2e
5.1 Isomers
C-C bonds that are constrained in a cyclic structure can not freely rotate
Although the two molecules below have the same connectivity, they are NOT identical.
The naming system we have learned thus far would give them the same name, but they are NOT identical, so we need to learn additional nomenclature rules…to be continued
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

5. Klein, Organic Chemistry 2e
5.1 Isomers
To maintain orbital overlap in the pi bond, C=C double bonds can not freely rotate.
Although the two molecules below have the same connectivity, they are NOT identical
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

6. Klein, Organic Chemistry 2e
5.1 Isomers
Identify the following pairs as either constitutional isomers, stereoisomers, or identical. EXPLAIN
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

7. Klein, Organic Chemistry 2e
5.1 Isomers
With rings and with C=C double bonds, cis-trans notation is used to distinguish between stereoisomers
Cis – identical groups are positioned on the SAME side of a ring
Trans – identical groups are positioned on OPPOSITE sides of a ring
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

8. Klein, Organic Chemistry 2e
5.1 Isomers
Cis – identical groups are positioned on the SAME side of a C=C double bond
Trans – identical groups are positioned on OPPOSITE sides of a C=C double bond
Practice with SkillBuilder 5.1
trans because of the H's
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

9. Klein, Organic Chemistry 2e
5.1 Isomers
Identify the following as either cis, trans, or neither. EXPLAIN
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

10. Klein, Organic Chemistry 2e
5.2 Stereoisomers
Beyond cis-trans isomers, there are many other important stereoisomers
To identify such stereoisomers, we must be able to identify chiral molecules
A chiral object is NOT identical to its mirror image
You are a chiral object. Look in a mirror and raise your right hand. Your mirror image raises his or her left hand.
You can test whether two objects are identical by seeing if they are superimposable.
Can you be superimposed upon your mirror image?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

11. Klein, Organic Chemistry 2e
5.2 Stereoisomers
Some other chiral objects include gloves. HOW?
Think of some other examples of chiral everyday objects
Chirality is important in molecules.
Because two chiral molecules are mirror images, they will have many identical properties, but because they are not identical, their pharmacology may be very different
Visualizing mirror images of molecules and manipulating them in 3D space to see if they are superimposable can be VERY challenging
It is highly recommended that you use handheld models as visual aids until you get more experience
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

12. Klein, Organic Chemistry 2e
5.2 Stereoisomers
Chirality most often results when a carbon atom is bonded to 4 unique groups of atoms.
Make a handheld model to prove to yourself that they are NOT superimposable
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

13. Klein, Organic Chemistry 2e
5.2 Stereoisomers
When an atom such as carbon forms a tetrahedral center with 4 different groups attached to it, it is called a chirality center (aka stereocenter or stereogenic center)
Analyze the attachments for each chirality center below
Practice with SkillBuilder 5.2
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

14. Klein, Organic Chemistry 2e
5.2 Stereoisomers
Identify all of the chirality centers (if any) in the following molecules
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

15. Klein, Organic Chemistry 2e
5.2 Enantiomers
Some stereoisomers can also be classified as enantiomers
Enantiomers are TWO molecules that are MIRROR IMAGES but are NONidentical and NONsuperimposable
For the pair below, draw in the missing enantiomer
Make handheld models for both structures to verify that they are NONidentical mirror images
Practice with SkillBuilder 5.3
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

16. Klein, Organic Chemistry 2e
5.2 Enantiomers
What is the relationship between the two molecules below?
Given that the molecules are so similar, how is it possible that our noses can distinguish between them?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e