general, organic, and biological chemistry copyright © 2010 pearson education, inc.1 chapter 17...
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General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1
Chapter 17 Lipids
17.4Chemical Propertiesof Triacylglycerols
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The chemical reactions of triacylglycerols are similar
to those of alkenes and esters.
In hydrogenation, double bonds in unsaturated fatty acids react with H2 in the presence of a Ni or Pt catalyst.
In hydrolysis, ester bonds are split by water in the presence of an acid, a base, or an enzyme.
Chemical Properties of Triacylglycerols
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Hydrogenation of Glyceryl Trioleate
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Hydrogenation of Oils
The hydrogenation of oils converts double bonds to single bonds adds hydrogen (H2) to the carbon atoms of double
bonds increases the melting point produces solids such as margarine and shortening
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What product(s) is obtained from the completehydrogenation of glyceryl trioleate?
1) glycerol and 3 oleic acids
2) glyceryltristearate
3) glycerol and 3 stearic acids
Learning Check
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What product(s) is obtained from the completehydrogenation of glyceryl trioleate?
2) glyceryltristearate
Solution
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Olestra, A Fat Substitute
Olestra don’t consume much in a short term used in foods as an artificial fat: potato chips, etc. sucrose linked by ester bonds to several long-chain
fatty chains not broken down, not absorbed (too big) in the intestinal
tract: Side effects: abdominal cramp, carries fat-soluble
Vitamin (A, D, E & K) with it to waste them.
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Unsaturated fatty acids can be Cis with bulky groups on the same side of C═C
Trans have bulky groups on opposite sides of C═C
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Cis and Trans Fatty Acids
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Trans Fatty Acids and Hydrogenation Trans fatty acids are formed during hydrogenation when cis double
bonds are converted to trans double bonds in the body behave like saturated fatty acids are estimated to make up 2 to 4% of our total
calories in several studies are reported to raise LDL-
cholesterol and lower HDL-cholesterol
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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
a label states “partially” or “fully hydrogenated” if the fats contain trans fatty acids
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Formation of Trans Fats
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Learning Check
Identify each statement as true (T) or false (F).
A. There are more unsaturated fats in vegetable oils.
B. Vegetable oils have higher melting points than fats.
C. Hydrogenation of oils converts some cis-double bonds to trans-double bonds.
D. Animal fats have more saturated fats.
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Solution
Identify each statement as true (T) or false (F).
T A. There are more unsaturated fats in vegetable oils.
F B. Vegetable oils have higher melting points than fats.
T C. Hydrogenation of oils converts some cis-double bonds to trans-double bonds.
T D. Animal fats have more saturated fats.
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Hydrolysis
In acid or enzyme hydrolysis, water adds to the ester bonds triacylglycerols split into glycerol and three fatty acids an acid or enzyme catalyst is required
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Base Hydrolysis (Saponification )
In base hydrolysis (saponification), a triacylglycerol reacts with a strong base a triacylglycerol splits into glycerol and the salts of
fatty acids soaps (salts of fatty acids) form
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Saponification
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What products are obtained from the complete hydrolysis of glyceryl trioleate?
1) glycerol and 3 oleic acids
2) glyceryl tristearate
3) glycerol and 3 stearic acids
Learning Check
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What products are obtained from the complete hydrolysis of glyceryl trioleate?
1) glycerol and 3 oleic acids
Solution
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Learning Check
Draw the condensed structural formula of theproduct of the following reaction.
O
O
CH2
O
O
CH
CH2 O
O
C
C
C
(CH2)7 CH CH
CHCH(CH2)7
CHCH(CH2)7
(CH2)5 CH3
(CH2)5 CH3
(CH2)5 CH3
+ 3H2
Ni
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Solution
CH2 (CH2)14
CH2
CH O C
O
O C
O
O
O
C
(CH2)14 CH3
(CH2)14 CH3
CH3