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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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