Lipids
Types of Lipids
Fatty Acids
Fats, and Oils
Chemical Properties of Triglycerides
1
Types of Lipids
• Lipids with fatty acids
Waxes
Fats and oils (trigycerides)
Phospholipids
Sphingolipids
• Lipids without fatty acids
Steroids
2
Fatty Acids
•
•
•
•
Long-chain carboxylic acids
Insoluble in water
Typically 12-18 carbon atoms (even number)
Some contain double bonds
corn oil contains 86%
unsaturated fatty acids and
14% saturated fatty acids
3
Saturated and Unsaturated
Fatty Acids
Saturated = C–C bonds
Unsaturated = one or more C=C bonds
COOH
palmitic acid, a saturated acid
COOH
palmitoleic acid, an unsaturated fatty acid
4
Structures
Saturated fatty acids
• Fit closely in regular pattern
COOH
COOH
COOH
Unsaturated fatty acids
H
• Cis double bonds
H
C C
cis double bond
COOH
5
Properties of Saturated
Fatty Acids
• Contain only single C–C bonds
• Closely packed
• Strong attractions between chains
• High melting points
• Solids at room temperature
6
Properties of Unsaturated
Fatty Acids
• Contain one or more double C=C bonds
• Nonlinear chains do not allow molecules
to pack closely
• Few interactions between chains
• Low melting points
• Liquids at room temperature
7
Learning Check L1
How would the melting point of stearic
acid compare to the melting points of oleic
acid and linoleic acid? Assign the melting
points of –17°C, 13°C, and 69°C to the
correct fatty acid. Explain.
stearic acid (18 C) saturated
oleic acid (18 C) one double bond
linoleic acid (18 C) two double bonds
8
Solution L1
Stearic acid is saturated and would have a
higher melting point than the unsaturated
fatty acids. Because linoleic has two
double bonds, it would have a lower mp
than oleic acid, which has one double
bond.
stearic acid mp 69°C
oleic acid mp 13°C
9
linoleic acid mp -17°C
Fats and Oils
Formed from glycerol and fatty acids
O
CH2 OH
CH
OH
CH2
OH
glycerol
HO C
O
+
(CH2)14CH3
HO C (CH2)14CH3
O
HO C
(CH2)14CH3
palmitic acid (a fatty acid)
10
Triglycerides (triacylglcerols)
Esters of glycerol and fatty acids
ester bonds
O
CH2
O
C
(CH2)14CH3 + H2O
O
CH
CH2
O
O
C (CH2)14CH3
O
C
+ H 2O
(CH2)14CH3 +
H 2O
11
Learning Check L2
What are the fatty acids in the following
triglyceride?
O
CH2
O
C
(CH2)16CH3
O
CH
CH2
O
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
12
Solutions L2
What are the fatty acids in the following
triglyceride?
O
CH2
O
C
O
CH
CH2
Stearic acid
(CH2)16CH3
Oleic acid
O
C (CH2)7CH CH(CH2)7CH3
O
Myristic acid
O C (CH2)12CH3
13
Properties of Triglycerides
Hydrogenation
• Unsaturated compounds react with H2
• Ni or Pt catalyst
• C=C bonds
C–C bonds
Hydrolysis
• Split by water and acid or enzyme catalyst
• Produce glycerol and 3 fatty acids
14
Hydrogenation
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
O
CH
CH2
O
O
C (CH2)5CH CH(CH2)7CH3
O
C
+ 3 H2
Ni
(CH2)5CH CH(CH2)7CH3
15
Product of Hydrogenation
O
CH2
O
C
(CH2)14CH3
O
CH
CH2
O
O
C (CH2)14CH3
O
C
(CH2)14CH3
Hydrogenation converts double bonds in oils
to single bonds. The solid products are used
to make margarine and other hydrogenated
items.
16
Hydrolysis
Triglycerides split into glycerol and three
fatty acids (H+ or enzyme catalyst)
O
CH2
O
C
(CH2)14CH3
O
CH
CH2
O
O
H+
C (CH2)14CH3
O
C
+3 H2O
(CH2)14CH3
CH2 OH
CH
OH
CH2
OH
O
+
3 HO C
(CH2)14CH3
17
Saponification and Soap
• Hydrolysis with a strong base
• Triglycerides split into glycerol and the
salts of fatty acids
• The salts of fatty acids are “soaps”
• KOH gives softer soaps
18
Saponification
O
CH2
O
C
(CH2)16CH3
O
CH
CH2
O
O
C
O
C
(CH2)16CH3 + 3 NaOH
(CH2)16CH3
CH2 OH
CH
CH2
O
+OH + 3 Na O C (CH2)14CH3
salts of fatty acids (soaps)
OH
19
Learning Check L3
What are the products obtained from the
complete hydrogenation of glyceryl
trioleate?
(1) Glycerol and 3 oleic acids
(2) Glyceryltristearate
(3) Glycerol and 3 stearic acids
20
Solution L3
What are the products obtained from the
complete hydrogenation of glyceryl
trioleate?
2. Glyceryltristearate
21