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Practice Problems 26.4 Identifying Isoprene Units in a Terpene
STEP 1 Count the
number of carbon atoms
in order to identify the
number of isoprene units.
STEP 2 Look for any methyl groups and
the carbon atoms to which they are attached.
C
STEP 3 Using trial and
error, identify the isoprene
units that have the correct
branching structure.
One branch
2
1
C
4
3
C
C
C
C
O
10 Carbon atoms=
2 Isoprene units
C
O
These three
carbon atoms must
be grouped together
C
C
C
C
O
These two carbon
atoms must be
grouped together
C
C
C
C
C
C
or
C
C
C
C
C
C
O
C
C
O
Try Problems 26.25, 26.26, 26.55
Practice Problems
26.29 Identify each of the following compounds as a wax,
triglyceride, phospholipid, steroid, prostaglandin, or terpene.
(a) Stanozolol
(c) Tristearin
(e) PGF2
(b) Lycopene
(d) Distearoyl lecithin
( f ) Pentadecyl octadecanoate
26.30 Predict the product(s) formed when tripalmitolein is
treated with each of the following reagents.
Note: Most of the Problems are available within
WileyPLUS, an online teaching and learning solution.
(b) A diglyceride constructed from one equivalent of glycerol
and two equivalents of myristic acid
(c) A monoglyceride constructed from one equivalent of glycerol and one equivalent of myristic acid
26.37 Identify whether hexane or water would be more
appropriate for extracting terpenes from plant tissues. Explain
your choice.
(a) Excess H2, Ni
26.38 Identify each of the following fatty acids as saturated
(b) Excess NaOH, H2O
or unsaturated.
26.31 Draw two different cephalins that contain one lauric
(a) Palmitic acid
(d) Lauric acid
acid residue and one myristic acid residue. Are both of these
compounds chiral?
26.32 Draw an optically active triglyceride that contains one
palmitic acid residue and two myristic acid residues. Will this
compound react with molecular hydrogen in the presence of a
catalyst?
26.33 Which of the following compounds are lipids?
(a) l-Threonine
(c) Lycopene
(e) Palmitic acid
(g) Testosterone
(b) 1-Octanol
(d) Trimyristin
(f ) d-Glucose
(h) d-Mannose
26.34 Draw the structure of trans-oleic acid.
26.35 Tristearin is less susceptible to becoming rancid than
triolein. Explain.
26.36 Arrange the following compounds in order of increasing water solubility.
(a) A triglyceride constructed from one equivalent of glycerol
and three equivalents of myristic acid
klein_c26_1229-1267hr.indd 1265
(b)Myristic acid
(e)Linoleic acid
(c) Oleic acid
(f) Arachidonic acid
26.39 Which of the fatty acids in the previous problem has
four carbon-carbon double bonds?
26.40 Which of the following statements applies to triolein?
(a) It is a solid at room temperature.
(b) It is unreactive toward molecular hydrogen in the presence
of Ni.
(c) It undergoes hydrolysis to produce unsaturated fatty acids.
(d) It is a complex lipid.
(e) It is a wax.
( f ) It has a phosphate group.
26.41 Identify which of the following statements applies to
tristearin.
(a) It is a solid at room temperature.
(b) It is unreactive toward molecular hydrogen in the presence
of Ni.
(c) It undergoes hydrolysis to produce unsaturated fatty acids.
(d) It is a complex lipid.
(e) It is a wax.
( f ) It has a phosphate group.
11/24/10 6:35 PM
1266 CHAPTER
26 Lipids
26.42 One of the compounds present in carnauba wax
26.45 Draw a mechanism for the base-catalyzed transesteri-
was isolated, purified, and then treated with aqueous sodium
hydroxide to yield an alcohol with 30 carbon atoms and a
­carboxylate ion with 20 carbon atoms. Draw the likely structure
of the compound.
fication of trimyristin using ethanol in the presence of sodium
hydroxide.
26.46 Draw the structure of an optically inactive triglycer-
26.43 Draw the structures of trimyristin and tripalmitin and
ide that contains two oleic acid residues and one palmitic acid
­residue.
determine which is expected to have the lower melting point.
Explain your choice.
26.47 Draw the structure of an optically active triglyceride
26.44 Draw a mechanism for the transesterification of
that contains two oleic acid residues and one palmitic acid
­residue.
t­ rimyristin using excess isopropanol in the presence of an acid
­catalyst.
26.48 Draw the enantiomer of cholesterol.
26.49 Circle the isoprene units in each of the following ­compounds
(a)
Bisabolene
(b)
Flexibilene
(c)
Humulene
OH
OH
(d)
Vitamin A
(e)
(f)
Geraniol
Sabinene
26.50 Sphingomyelins are lipids with the following general structure:
Fatty acid residue
R
H
O
N
–
O
O
P
OH
O
N
O
±
Sphingomyelins
(a) Identify the polar head and all hydrophobic tails in
­sphingomyelins.
klein_c26_1229-1267hr.indd 1266
(b) Do sphingomyelins have the appropriate structural features
and three-dimensional geometry necessary to be major
constituents of lipid bilayers?
11/26/10 2:36 PM