Transcript chemistry.csudh.edu

Chapter 12 Unsaturated
Hydrocarbons
12.3
Addition Reactions
1
Addition Reactions
In alkene and alkynes
• The double or triple
bond is easily broken,
which makes double
and triple bonds very
reactive.
In addition reactions,
reactants are added to
the carbon atoms in the
double or triple bond.
2
Hydrogenation
In hydrogenation,
• Hydrogen atoms add to the carbon atoms of a double
bond or triple bond.
• A catalyst such as Pt or Ni is used to speed up the
reaction.
H
H 2C
CH 2 + H 2
Pt
H 2C
H
HC
CH
+
2H 2
Ni
HC
H
H
CH 2
H
CH
H
3
Hydrogenation of Oils
Adding H2 to double
bonds in vegetable
oils produces
• Compounds with
higher melting
points.
• Solids at room
temperature such
as margarine,
soft margarine,
and shortening.
4
Learning Check
Write an equation for the hydrogenation of 1-butene
using a platinum catalyst.
5
Solution
Write an equation for the hydrogenation of 1-butene using
a platinum catalyst.
Pt
CH2=CH─CH2─CH3 + H2
CH3─CH2─CH2─CH3
6
Trans Fats
In vegetable oils, the unsaturated fats usually contain
cis double bonds.
• During hydrogenation, some cis double bonds are
converted to trans double bonds (more stable)
causing a change in the fatty acid structure.
• If a label states “partially” or “fully hydrogenated”, the
fats contain trans fatty acids.
7
Learning Check
(1) True or (2) False
A. ____ There are more unsaturated fats in vegetable oils.
B. ____ Hydrogenation converts some cis-double bonds to
trans- double bonds.
C. ____ Animal fats have more unsaturated fats.
8
Solution
(1) True or (2) False
A. 1 There are more unsaturated fats in vegetable oils.
B. 1 Hydrogenation of oils converts some cis-double
bonds to trans- double bonds.
C. 2 Animal fats have more unsaturated fats.
9
Learning Check
Write the product of each the following.
Pt
CH3─CH=CH─CH3 + H2
Pt
+ H2
10
Solution
Pt
1. CH3─CH=CH─CH3 + H2
2.
+ H2
CH3─CH2─CH2─CH3
Pt
11
Hydration
In the addition reaction called hydration,
• an acid H+ catalyst is required.
• water (HOH) adds to a double bond.
• an H atom bonds to one C in the double bond.
• an OH bonds to the other C.
H OH
H+
│ │
CH3─CH=CH─CH3 + H─OH
CH3─CH─CH─CH3
12
Hydration
When hydration occurs with a double bond that has an
unequal number of H atoms,
• the H atom bonds to the C in the double bond with the
more H.
• the OH bonds to the C in the double bond with the
fewer H atoms.
OH H
H+
│ │
CH3─CH=CH2 + H─OH
CH3─CH─CH2
13
Learning Check
Write the product for the hydration of each of the
following:
H+
1. CH3─CH2─CH=CH─CH2─CH3 + HOH
CH3
│
H+
2. CH3─C=CH─CH2─CH3 + HOH
H+
3.
+ HOH
14
Solution
1.
2.
H OH
│
│
CH3─CH2─CH─CH─CH2─CH3
CH3
│
CH3─C─CH─CH2─CH3
│ │
OH H
OH
3.
H
15