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Home , Lauric acid, Stearic acid, Trimyristin, Triolein, Tripalmitin

692 CHAPTER 26

Solutions

26.1 O O

(CH2)29CH3 O OH + HO (CH2)29CH3 CH3(CH2)14 CH3(CH2)14

26.2 O O

26.3. a) ° b) triarachadin c) d) tristearin

26.4. tripalmitolein, , and tristearin

26.5. The residues in triarachadin have more carbon atoms than the fatty acid residues in tristearin. Therefore, triarachadin is expected to have a higher . It should be a solid at room temperature, and should therefore be classified as a , rather than an . Therefore, made from will also have a low melting point.

26.6. a) All three fatty acid residues are saturated, with either 16 or 18 carbon atoms, so the is expected to have a high melting point. It should be a solid at room temperature, so it is a fat. b) All three fatty acid residues are unsaturated, so the triglyceride is expected to have a low melting point. It should be a liquid at room temperature, so it is an oil.

26.7. O

O O O

O a) O b) Tristearin c) The melting point of tristearin is higher than triolein. d) CHAPTER 26 693

26.8. O O

O O O O O O

O O

O O

O O

O O O O O O

O O O O

26.9. O

Na O OH O OH Na O OH

Na O O

26.10. O

O O O

O

O

26.11 O

O O O

Not a O chirality center O

694 CHAPTER 26

26.12. Each of the three moieties is hydrolyzed via the following mechanism: H Me H HO O O HO O H HO O Me Me O H Me O H Me O O O O

H O Me H

H O Me O H O HO O Me Me Me OH O OH O O H

26.13. OH O OH + O OH (three equivalents)

26.14. a) Hydroxide functions as a catalyst by establishing an equilibrium in which some ethoxide ions are present.

HO + HOEt H2O + OEt ethoxide Then, each ester moiety undergoes via the following mechanism:

O OOEt O O O OEt H H Et Et O O OO OH O b) Hydroxide could function as a nucleophile and triglyceride would undergo hydrolysis rather than transesterification.

26.15. O O

O O O O O O

O O O O P N P N O O O O a) b)

c) No. The C2 position would no longer be a chirality center. CHAPTER 26 695

26.16. O O

O O O O O O

O O O O P NH3 P NH3 O O O O a)

b) Yes. The C2 position would still be a chirality center.

26.17.

O O O

O R O R O R O O O O O O R R R O O O O O O P P P O O O O O O

26.18. Octanol has a longer hydrophobic tail than hexanol and is therefore more efficient at crossing the nonpolar environment of the cell membrane.

26.19. No. Glycerol has three OH groups (hydrophilic) and no hydrophobic tail. It cannot cross the nonpolar environment of the cell membrane.

26.20. A ring-flip is not possible for trans-decalin because one of the rings would have to achieve a geometry that resembles a six-membered ring with a trans-alkene, which is not possible. The ring fusions of all resemble the ring fusion in trans-decalin, so cholesterol cannot undergo ring-flipping.

Hypothetical ring flip

696 CHAPTER 26

26.21. axial equatorial Me Me Me equatorial Me a) axial

axial Me Me axial

Me equatorial Me b) axial

axial axial CH3 CH3 H O

H H OH H c) axial

26.22. OH OH Et H C C H H H HO H H H H O O H oxymetholone norgestrel

26.23. O O O

HO OH H

H H O

CHAPTER 26 697

26.24. a) PGE1 b) PGF1α

26.25. O OH OH

a) menthol b) grandisol c) carvone

26.26. a) Yes, it has 10 carbon atoms, which are comprised by the joining of two isoprene units. b) No, it has 11 carbon atoms. c) No, it has 11 carbon atoms. d) No. It has 10 carbon atoms, but the branching pattern cannot be achieved by joining two isoprene units.

26.27.

- OPP

OPP

OPP

OPP OPP B H

698 CHAPTER 26

26.28.

- OPP OPP OPP OPP H

B OPP

- OPP

OPP geranyl pyrophosphate

H OPP OPP B

farnesyl H pyrophosphate

B

ααα-farnesene 26.29. a) b) terpene c) triglyceride d) e) f) wax

26.30. O

O O O

O a) O

CHAPTER 26 699

OH O

OH + Na O b) OH (three equivalents)

26.31. Both compounds are chiral:

O O

O O O O O O

O O O O P NH3 P NH3 O O O O

26.32. The fatty acid residues in this triglyceride are saturated, and will not react with molecular hydrogen. O

O O O

O O

26.33. a) not a b) a lipid c) a lipid d) a lipid e) a lipid f) not a lipid g) a lipid h) not a lipid

26.34. O

HO

26.35. The fatty acid residues of tristearin are saturated and are therefore less susceptible to auto-oxidation than the unsaturated fatty acid residues in triolein.

26.36. a < b < c 700 CHAPTER 26

26.37. Water would not be appropriate because it is a polar , and terpenes are nonpolar compounds. is a nonpolar solvent and would be suitable.

26.38. a) saturated b) saturated c) unsaturated d) saturated e) unsaturated f) unsaturated

26.39.

26.40. a) No. It is an oil. b) No. It is reactive towards molecular hydrogen in the presence of Ni. c) Yes. It undergoes hydrolysis to produce unsaturated fatty acids. d) Yes. It is a complex lipid because it undergoes hydrolysis. e) No. It is not a wax. f) No. It does not have a phosphate group.

26.41. a) Yes. It is a fat. b) Yes. It is unreactive towards molecular hydrogen in the presence of Ni. c) No. It undergoes hydrolysis to produce fatty acids that are saturated. d) Yes. It is a complex lipid because it undergoes hydrolysis. e) No. It is not a wax. f) No. It does not have a phosphate group.

26.42. 20 CARBON ATOMS O 30 CARBON ATOMS O

26.43. Trimyristin is expected to have a lower melting point than tripalmitin because the former is comprised of fatty acid residues with fewer carbon atoms (14 instead of 16). O O

O O O O O O

O O

O O trimyristin tripalmitin

CHAPTER 26 701

26.44. Each of the three ester moieties is hydrolyzed via the following mechanism: H H O HO HO O O HO O H HO O H O O O O

H O H

HO H O O HO O

OH O OH O O H

26.45. See the solution to Problem 26.14.

26.46. O

O O O

O

O

26.47.

O

O

O O O

O

26.48. H

CH3 H CH3 H

H H HO 702 CHAPTER 26

26.49.

a) bisabolene b) flexibilene c) humulene

OH

OH d) Vitamin A e) geraniol f) sabinene

26.50. Hydrophobic tails R Polar Head H O N O O P N O OH O a) b) Yes, they have one polar head and two hydrophobic tails.

26.51. H H

CH3 CH3 H H CH3 H CH3 H

H H H H HO HO a) O O

b) The methyl group (C19) provides steric hindrance that blocks one side of the π bond, and only the following is obtained: H

CH3 H CH3 H

H H HO O CHAPTER 26 703

26.52. OH

H Br H H HO a) Br O

H

H H b) HO OEt

H

H H c) EtO O

O

H O H H d) O

26.53. The compound is chiral.

R O O O O O R R O O CH O O O O 2 O O O O R R R O O O O R R

26.54. a) H2, Ni b) H2, Ni, followed by NaOH, followed by EtI. c) H2, Ni, followed by LAH, followed by H2O d) O3, followed by DMS, followed by Na2Cr2O7 and H2SO4 e) H2, Ni, followed by PBr3 and Br2, followed by H2O 704 CHAPTER 26

26.55. a) Limonene is comprised of 10 carbon atoms and is, therefore, a monoterpene. b) The compound does not have any chirality centers and is, therefore, achiral: Br Br

c) O H O O + O H

26.56.

OH + HO OH H3O NaBH4 O O OH O MeOH H O OH H

Excess O

Cl trimyristin py 26.57. a) and have a glycerol backbone connected to three fatty acid residues. Plasmalogens also have a glycerol backbone, but it is only connected to two fatty acid residues. The third group is not a fatty acid residue.

b) OR' OH R" O Na HO O R O Na O

c) O

HO

OH O

OH HO

OH O

H