Chapter 19 & 20 Esters, Amides and Carbohydrates

1. Chemistry B11 Chapter 19 & 20 Esters, Amides and Carbohydrates

2. Esters

4. ' R C O H R C O R - ' R C - O H H O R O O = H2SO4 = + H2O An alcohol A carboxylic acid An ester Formation of Esters O = A carboxylic acid Fischer Esterification

5. Naming of Esters • Name the alkyl group from the alcohol –OR. • Followed by name of the acid in which the suffix “-ic acid” is replaced by suffix “-ate”. acid alcohol methyl CH3 —C—O—CH3 ethanoate IUPAC: methyl ethanoate (acetate)common:methylacetate O

6. Naming of Esters propyl CH3 —C—O —CH2—CH2—CH3 Propyl ethanoate (IUPAC) Propyl acetate (common) O CH3—CH2 —C—O—CH2—CH3 Ethyl propanoate O

7. Fischer Esterification CH3 —C—OH+HO—CH2—CH3 CH3 —C—O—CH2—CH3 +H2O O H2SO4 Ethanoic acid (Acetic acid) Ethanol (Ethyl alcohol) Ethyl ethanoate (Ethyl acetate)

8. R C O R ' O O = = - + ' R C - O H H O R + H2O An alcohol A carboxylic acid An ester Properties of Esters Esters give flowers and fruits their pleasant fragrances and flavors. Hydrolysis: reaction with water. (breaking a bond and adding the elements of water) Heat Acid

9. ' R C O R O O = = - + O O Heat ' + + NaOH R C O- N a - O R H = = - + H2O + + NaOH C O C O- N a CH3 CH2CH3 CH3 CH3CH2OH An alcohol A sodium salt An ester Ethanol Sodium acetate Ethyl Ethanoate Properties of Esters Saponification (Hydrolysis): an ester reacts with a hot aqueous base.

10. Amides

11. Amides In an amide, the -OH group in the carboxyl group of a carboxylic acid is replaced by an Amino group (-NH2). CH3 —C—OHCH3 —C —NH2 O O = =

12. R C O H O O = = Heat ' ' - H N HR R C NH R + H2O A carboxylic acid An Amine An amide R C - O H H O 2 Formation of Amides O = A carboxylic acid O O C H C - O H + H HN C H C H C H C - N H C H C H + 3 3 2 3 2 3 Ethanamine N-ethylethanamide Acetic acid

13. Naming of Amides Change the end of the name of the carboxylic acids from “-oic acid” to “-amide”. methanoicacid H–C–NH2 methanamide (IUPAC) propanoicacid CH3–CH2–C–NH2 propanamide (IUPAC) O = O =

14. Naming of Amides CH3–C–NH–CH3 N-methylethanamide CH3–CH2–C–N(CH3)2 N,N-dimethylpropanamide CH3–C–N(CH2CH3)2 N,N-diethylethanamide O = O = O =

15. Properties of Amides Such as esters: Hydrolysis in hot aqueous acid or base

16. Carbohydrates • Produced by photosynthesis in plants. • The major source of energy from our diet. • Composed of the elements C, H, and O. Cn(H2O)n Photosynthesis 6CO2 + 6H2O + energy C6H12O6 + 6O2 Respiration glucose

17. Carbohydrates • The most abundant organic compounds in the plant world. • 3/4 of the weight of plants. • 1% of the weight of animals and humans (they do not store). • 65% of the foods in our diet.

18. Carbohydrates H+ or enzyme 1. Monosaccharide + H2O no hydrolysis H+ or enzyme 2. Disaccharide + H2O two monosaccharide units + H+ or enzyme 3. Polysaccharide + many H2O many monosaccharide units

19. Monosaccharides A carbohydrate that cannot be split or hydrolyzed into smaller carbohydrates. Monosaccharides are carbohydrates with: • 3-9 carbon atoms • A carbonyl group (aldehyde or ketone) • Several hydroxyl groups Cn(H2O)n CnH2nOn ║ C ─ H │ H─ C ─ OH │ H─ C ─ OH │ CH2OH O

20. Monosaccharides - Aldose O ║ C ─ H aldose │ H─ C ─ OH │ H─ C ─ OH │ CH2OH an aldotetrose (Erythose) Aldose is monosaccharide: • With an aldehyde group and many hydroxyl (-OH) groups. • triose (3C atoms) • tetrose (4C atoms) • pentose (5 C atoms) • hexose (6 C atoms) “Aldo-” + suffix

21. Monosaccharides - Ketose CH2OH │ C = O ketose │ H─ C ─ OH │ H─ C ─ OH │ H─ C ─ OH │ CH2OH a ketohexose (Fructose) Ketose is monosaccharide: • With a ketone group and many hydroxyl (-OH) groups. • triose (3C atoms) • tetrose (4C atoms) • pentose (5 C atoms) • hexose (6 C atoms) “Keto-” + suffix

22. Some important Monosaccharides Glucose (Dextrose) (C6H12O6, aldohexose) – Blood sugar • The most abundant monosaccharide • Is found in fruits, vegetables, corn syrup, and honey. • Is found in disaccharides such as sucrose, lactose, and maltose. • Makes up polysaccharides such as starch, cellulose, and glycogen.

23. Some important Monosaccharides Glucose(Dextrose) - Normal blood glucose levels are 70-110 mg/dL. - Excess glucose is stored as the polysaccharide glycogen or as fat. - Insulin (a protein produced in the pancreas)regulates blood glucose levels by stimulating the uptake of glucose into tissues or the formation of glycogen. - Patients with diabetes produce insufficient insulin to adequately regulate blood sugar levels, so they must monitor their diet and/or inject insulin daily.

24. Some important Monosaccharides Fructose (C6H12O6, ketohexose), • Is the sweetest of the carbohydrates. • Is found in fruit juices and honey (fruit sugar). • In bloodstream, it is converted to its isomer, glucose. • Is bonded to glucose in sucrose (a disaccharide known as table sugar).

25. Some important Monosaccharides Galactose (C6H12O6, aldohexose), • Has a similar structure to glucose except for the –OH on Carbon 4. • Cannot find in the free form in nature. • Exist in the cellular membranes of the brain and nervous system. • Combines with glucose in lactose (a disaccharide and a sugar in milk).

26. Disease - Galactosemia Galactosemia missing the enzyme that convert galactose to glucose. Accumulation of galactose in the blood and tissues. Mental retardation and cataract Solution: removing the galactose from food: no milk.

27. C H O Convert to Fischer Projection C H O H O H H C O H C H O H C H O H 2 2 Fischer Projections - Horizontal lines represent bonds projecting forward from the stereocenter. - Vertical lines represent bonds projecting to the rear. - Only the stereocenter (tetrahedral carbon) is in the plane. 3D 2D

28. Fischer Projections 1. Carbon with four different groups bonded to it. 2. The chiral carbon furthest from the carbonyl group (-CHO). * * * * * * * * H HO L - glucose D - glucose Naturally occurring enantiomer

29. Cyclic Structure – Haworth Structure 1 1 Anomeric carbon 1 1 1 Alpha (α) Beta () More stable form Anomers

30. Cyclic Structure – Haworth Structure  1 1  -Glucose-Glucose 1 1 -Galactose-Galactose

31. CH2OH OH HOCH2 HOCH2 2 2 HO HO H H H OH H CH2OH OH H OH H -D-fructose-D-fructose Cyclic Structure – Haworth Structure 1 Anomeric carbon OH C=O 5 2

32. Cyclic Structure – Haworth Structure  1 1  -Glucose-Glucose Humans have -amylase (an enzyme) and they can digest starch products such as pasta (contain-glucose) Humans do not have β-amylase (an enzyme) and they cannot digest cellulose such as wood or paper (containβ-glucose)

33. -D-glucose Open-chain form (acyclic) α-D-glucose Mutarotation Change in specific rotation that accompanies the equilibration of αand  anomers in aqueous solution. 36% 64% < 0.02%

34. Physical properties of Monosaccharides • Colorless • Sweet Tasting • Crystalline solids • Polar with high melting points (because of OH groups) • Soluble in water and insoluble in nonpolar solvents (H-bond because of OH groups)

35. OH Oxidation + Cu2O(s) + 2Cu2+ (Brike red) Benedict’s Reagent (blue) D - glucose D – gluconic acid Oxidation of Monosaccharides Aldonic acids Reducing sugars: reduce another substance.

36. Oxidation of Monosaccharides Rearrangement (Tautomerism) D-fructose (ketose) D-glucose (aldose)

37. Reduction of Monosaccharides Alditols Sugars alcohols: sweetners in many sugar-free (diet drinks & sugarless gum). Problem: diarrhea and cataract

38. Disaccharides • A disaccharide: • Consists of two monosaccharides linked by a glycosidic bond (when one –OH group reacts with another –OH group). • Glucose + Glucose Maltose + H2O • Glucose + Galactose Lactose + H2O • Glucose + Fructose Sucrose + H2O

39. Disaccharides The glycosidic bond joining the two rings can be alpha (a) or beta (b).

40. Disaccharides Maltose: • Is a disaccharide of two glucose molecules. • Has a α-1,4-glycosidic bond (between two α-glucoses). • Is obtained from the breakdown of starches. • Is used in cereals and candies. • Is a reducing sugar (carbon 1 can open to give a free aldehyde to oxidize).  -1,4-glycosidic bond  + 1 4 1 4 + H2O α-glucose α-glucose - maltose

41. Disaccharides Lactose: • Is a disaccharide of galactose and glucose. • Has a β -1,4-glycosidicbond (between β-galactoseandα-gulcose). • Is found in milk and milk products (almost no sweet). • Is a reducing sugar(carbon 1 can open to give a free aldehyde to oxidize).  -lactose

42. Disaccharides Sucrose: • Is found in table sugar (obtained from sugar cane and sugar beets). • Consists of glucose and fructose. • Has an α,β-1,2-glycosidic bond(between α-glucose and -fructose). • Is not a reducing sugar(carbon 1 cannot open to give a free aldehyde to oxidize). β-1,2-glycosidic bond

43. Disaccharides Sucrose: Sucrose is very sweet, but contains many calories. To reduce caloric intake, many artificial sweeteners have been developed. Aspartame, Saccharin, Sucralose These artificial sweeteners were discovered accidentally.

44. Artificial sweeteners Aspartame: It (sold as Equal) is hydrolyzed into phenylalanine, which cannot be processed by those individuals with the condition phenylketonuria.

45. Artificial sweeteners Saccharine: It (sold at Sweet’n Low) was used extensively during World War I. There were concerns in the 1970s that saccharin causes cancer.

46. Artificial sweeteners Sucralose: It (sold as Splenda) has a very similar structure to sucrose.

47. Polysaccharides • Polymers of many monosaccharides units. Amylose (20%) • Starch Amylopectin (80%) • Glycogen(animal starch in muscle and liver. It is hydrolyzed in our cells and provides energy ). • Cellulose(plant and wood structures). (starch that stores glucose in plants such as rice, potatoes, beans, and wheat).

48. Polysaccharides Amylose: • Is a polysaccharide of α-glucose in a continuous (unbranched) chain (helical or coil form). • Has α-1,4-glycosidic bonds between the α-glucose units (250 to 4000 units). α-1,4-glycosidic bond

49. Polysaccharides Amylopectin: • Is a polysaccharide of glucose units in branched chains. • Has α-1,4-glycosidic bonds between the α-glucose units. • Has α-1,6 bonds to branches of glucose units. (at about every 25 glucose units, there is a branch). • Both forms of starch are water soluble.

50. Polysaccharides Glycogen: - It is similar to amylopectin (more highly branched-every 10-15 units). - It is an energy storage molecule found in animals/humans. - It is stored mainly in the liver and in muscle cells. - When glucose is needed for energy, glucose units are hydrolyzed from the ends of the glycogen polymer. - Because glycogen is highly branched, there are many ends available for hydrolysis.