1. Molecular Representations
Organic Chemistry
Second Edition
David Klein
Chapter 2
Molecular Representations
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

2. 2.1 Representing Molecules
There are many ways to represent molecules
If you were representing a large molecule with 20 or more atoms, which structure would be most time consuming to draw?
Which structures give you the most information about the structure?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

3. 2.1 Representing Molecules
Given that there are three isomers of propanol (below), which structures above are adequate to represent only isopropanol and not its isomers?
Practice with SkillBuilder 2.1
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

4. 2.1 Representing Molecules
To draw large molecules quickly, a different type of representation is needed
Consider the antibiotic Amoxicillin. Its Lewis structure looks cluttered, and it would be very time consuming to draw
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

5. 2.2 Bond-line Structures
The Bond-line structure is easier to read and to draw
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

6. 2.2 Bond-line Structures
It may seem like a foreign language at first, because many of the atoms are not labeled
This type of representation is THE main way that chemists communicate, so it is a language you MUST master to be successful in organic chemistry
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

7. 2.2 Bond-line Structures
Like Lewis structures, lines are drawn between atoms to show covalent bonds
Atoms are bonded at angles (zigzag) that represent the actual geometry of the bond angles
What is the bond angle for sp3 hybridized carbon?
Carbon atoms are not labeled, but a carbon is assumed to be located at every corner or endpoint on the zigzag.
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

8. 2.2 Bond-line Structures
Like Lewis structures, lines are drawn between atoms to show covalent bonds
Carbon-Hydrogen bonds are omitted. WHY?
If the H atoms are omitted, how will we know how many H atoms are attached to a carbon?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

9. 2.2 Bond-line Structures
Practice identifying the location of and counting the number of carbon atoms in the structures below
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

10. 2.2 Bond-line Structures
Double bonds and triple bonds are represented as you might expect
Why is a triple bond written without zigzagging?
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

11. 2.2 Bond-line Structures
You must also be able to use the bond-line structure language to interpret the number and location of H atoms in a molecule
H atoms are not shown, but we can assume there are enough to complete the octet (4 bonds) for each carbon
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

12. 2.2 Bond-line Structures
You should practice bond-line structures until it becomes natural for you to see all of the carbon and hydrogen atom locations.
How many carbon and hydrogen atoms are in the following molecule?
Practice with SkillBuilder 2.2
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

13. 2.2 Bond-line Structures
If you are given a Lewis structure or condensed structure, you must also be able to draw the corresponding bond-line structure
Represent the bond angles with zigzags
Follow VSEPR and spread out the electron pairs on a central atom
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

14. 2.2 Bond-line Structures
If you are given a Lewis structure or condensed structure, you must also be able to draw the corresponding bond-line structure
Single bonds are axes of rotation, so be aware that they can rotate
Give alternative bond-line structures for the molecule below
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

15. 2.2 Bond-line Structures
If you are given a Lewis structure or condensed structure, you must also be able to draw the corresponding bond-line structure
Heteroatoms (atoms other than C and H) should be labeled with all hydrogen atoms and lone pairs attached
NEVER draw a carbon with more than 4 bonds!!
Practice with SkillBuilder 2.3
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

16. 2.2 Bond-line Structures
Draw bond-line representations for the following Lewis structures
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e

17. 2.2 Bond-line Structures
Draw bond-line representations for 3 possible isomers given the formula: C5H9ClO
Draw bond-line structures for 3 different rotational conformations for the molecule: CH2CH(CH2)4CH3
Copyright © 2015 John Wiley & Sons, Inc. All rights reserved.
Klein, Organic Chemistry 2e