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Alkenes and Alkynes

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Title: Slide 1 Author: Thomas Schultz Last modified by: John Created Date: 1/7/2009 2:54:16 AM Document presentation format: On-screen Show Other titles – PowerPoint PPT presentation

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Title: Alkenes and Alkynes


1
Alkenes and Alkynes Chapter 3
2
Alkene Introduction
  • Hydrocarbon with carbon-carbon double bonds
  • Sometimes called olefins, oil-forming gas
  • General formula CnH2n n2
  • Examples
  • n2 C2H4

3
Common Names
Usually used for small molecules. Examples
CH3
CH2CH2 CH2CH-CH3 CH2C-CH3 ethylene
propylene isobutylene
Vinyl carbons are the carbons sharing a double
bond in blue
Vinyl hydrogens are the hydrogens bonded to vinyl
carbons in red
4
IUPAC Nomenclature
  • Parent is longest chain containing the double or
  • triple bond.
  • -ane changes to ene (or -diene, -triene) for
  • double bonds, or yne (or diyne, -triyne).
  • Number the chain so that the double bond, or
  • triple bond has the lowest possible number.
  • In a ring, the double bond is assumed to be
  • between carbon 1 and carbon 2.


5
Name These Alkenes
6
Name These Alkenes
1-butene
7
Name These Alkenes
1-butene
2-methyl-2-butene
8
Name These Alkenes
1-butene

2-methyl-2-butene
3-methylcyclopentene
9
Name These Alkenes
1-butene
2-sec-butyl-1,3-cyclohexadiene
2-methyl-2-butene

3-methylcyclopentene
10
Name These Alkenes
1-butene
2-sec-butyl-1,3-cyclohexadiene
2-methyl-2-butene
3-n-propyl-1-heptene
3-methylcyclopentene
11
Alkene Substituents
Name ?
12
Alkene Substituents
Name Methylenecyclohexane
Name
13
Alkene Substituents
Name Methylenecyclohexane
Name vinylcyclohexane
14
Alkyne Common Names
  • Acetylene is the common name for the two carbon
    alkyne.
  • To give common names to alkynes having more than
    two carbons, give alkyl names to the carbon
    groups attached to the vinyl carbons followed by
    acetylene.

15
Alkyne Examples
16
Alkyne Examples
Isopropyl methyl acetylene
17
Alkyne Examples
Isopropyl methyl acetylene
sec-butyl Cyclopropyl acetylene
18
Cis-trans Isomerism
  • Similar groups on same side of double bond,
    alkene
  • is cis.
  • Similar groups on opposite sides of double bond,
  • alkene is trans.
  • Cycloalkenes are assumed to be cis.
  • Trans cycloalkenes are not stable unless the
    ring has at least 8 carbons.

19
Name these
20
Name these
trans-2-pentene
21
Name these
trans-2-pentene
22
Name these
trans-2-pentene
cis-1,2-dibromoethene
23
Which of the following show cis/trans
isomers? a. 1-pentene b. 2-pentene c.
1-chloro-1-pentene d. 2-chloro-1-pentene e.
2-chloro-2-pentene
24
Solution to the Question
25
Solution to the Question
26
Which of the following show cis/trans
isomers? a. 1-pentene-No b. 2-pentene- Yes c.
1-chloro-1-pentene- Yes d. 2-chloro-1-pentene-
No e. 2-chloro-2-pentene- yes
27
E-Z Nomenclature
  • Use the Cahn-Ingold-Prelog rules to assign
    priorities
  • to groups attached to each carbon in the double
  • bond. Highest priority is 1 and is the element
    with
  • the largest atomic number.
  • If high priority groups are on the same side,
    the
  • name is Z (for zusammen).
  • If high priority groups are on opposite sides,
    the
  • name is E (for entgegen).

28
Example, E-Z
2Z
5E
29
Example, E-Z
2Z
5E
3,7-dichloro-(2Z, 5E)-2,5-octadiene
30
Physical Properties
  • Low boiling points, increasing with mass.
  • Branched alkenes have lower boiling points.
  • Less dense than water.
  • Nonpolar (Hydrophobic)

31
Alkene Synthesis
Elimination Reactions
  • Dehydrohalogenation (-HX)
  • Dehydration of alcohols (-H2O)

Examples
Zaitsevs rule The major product contains the
most substituted double bond
32
Alkene Reactions
I. Addition Reactions
a. Hydration
H
O-H
H
CC
C-C
Follows Markovnikovs Rule
H-O-H
Alcohol
b. Hydrogenation
H
H
Catalyst
CC
C-C
Catalyst Ni, Pt, Pd
H-H
Alkane
c. Halogenation
X
X
C-C
CC
X-X
Dihalide
X Cl, Br, I
33
Regiospecificity
Markovnikovs Rule The proton (H) of an acid
adds to the carbon in the double bond that
already has the most Hs. Rich get richer.
H
O-H
Examples

H
H

H
C-C
H
H
CC
H-O-H
H
CH3
CH3
H
Major Products
H
Cl
H
H
C-C
CC
H-Cl
H
H
H
CH3
H
CH3
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