Alkenes

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Chapter 3
Alkenes Alkynes
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Unsaturation
Recall
pentane C5H12
cyclopentane C5H10
We refer to pentane as a saturated compound
because the carbon atoms have the maximum number
of possible substituents
We refer to cyclopentane as an unsaturated
compound because the carbon atoms do not have
the maximum number of possible substituents
Can you think of any other ways to make an
unsaturated molecule?
3
Double Triple Bonds
C5H12
C5H10
C5H8
0 of unsaturation
1 of unsaturation
2 of unsaturation
C5H8
C5H10
Multiple sites of unsaturation
Degree of unsaturation ( of double bonds) (2
of triple bonds) ( of rings)
4
Double Triple Bonds
CnH2n2
CnHn
CnH2n-2
C5H12
C5H10
C5H8
0 of unsaturation
1 of unsaturation
2 of unsaturation
C5H8
C5H10
Degree of unsaturation ( of double bonds) (2
of triple bonds) ( of rings)
5
Double Triple Bonds
CnH2n2
CnHn
CnH2n-2
C5H12
C5H10
C5H8
0 of unsaturation
1 of unsaturation
2 of unsaturation
1
C6H10BrCl
C5H8
C5H10
C8H10NOBr
4
Degree of unsaturation 2 (2 x Cs) Ns -
Hs - Halogens/2
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Double Triple Bonds
Alkenes
Alkynes
Alkanes
C5H12
C5H10
C5H8
pentane (n-pentane)
1-pentyne
1-pentene
C5H8
C5H10
2-pentene
2-pentyne
How do we name these guys?
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Rules for Naming Alkenes and Alkynes
1) Find the longest carbon chain containing the
multiple bond
2) Start numbering from the end closest to the
multiple bond
3) Finish as if you were naming an alkane only
use the appropriate suffix (e.g., -ene for a
double bond, -yne for a triple bond)
Lets try a practice problem
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Name That Organic Compound
pentene
1-
3,4-dimethyl-
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Name That Organic Compound
1,3-pentadiene
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Nomenclature of Alkenes
Common Terms You Should Know
Alkenes are also called olefins.
vinylic carbons
2-pentene
1
2
4
8
6
5
9
3
7
10
allylic carbons
5-allyl-4-vinyl-decane
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Alkene Factoids
rotate
rotate
Recall
butane (n-butane)
Now lets look at 2-butene
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Alkene Factoids
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E,Z Nomenclature
Sometimes cis and trans are ambiguous in such
cases we resort to the more formal E,Z
nomenclature.

• Look at each carbon atom and assign each group a
  priority

(The higher the molcular weight, the higher the
priority)

• Z if highest priority substituents on same side
  of double bond

• E if highest priority substituents on opposite
  side of double bond

A way to remember Ecross, Zame Zide
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Practice
1,1-dibromo-1-propene
(Z)-2-iodo-2-pentene
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Practice