Transcript Chapter 19-20 - Bakersfield College

Chemistry B11
Chapter 19 & 20
Esters, Amides and Carbohydrates
Esters
Formation of Esters
O
RCO H
A carboxylic acid
Fischer Esterification
O
RC- OH H-OR'
A carboxylic acid
An alcohol
H2SO4
O
RCOR' + H2O
An ester
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
O

methyl
CH3 — C—O —CH3
ethanoate
(acetate)
IUPAC: methyl ethanoate
common: methyl acetate
Naming of Esters
propyl
O
CH3 — C—O —CH2—CH2—CH3
Propyl ethanoate (IUPAC)
Propyl acetate (common)
O
CH3—CH2 —C—O—CH2—CH3
Ethyl propanoate
Fischer Esterification
O
CH3 — C—OH + HO—CH2—CH3
Ethanoic acid
Ethanol
(Acetic acid)
(Ethyl alcohol)
CH3 — C—O—CH2—CH3 + H2O
Ethyl ethanoate
(Ethyl acetate)
H2SO4
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)
O
RCOR' + H2O
An ester
Heat
Acid
O
RC- OH
A carboxylic acid
+
H-OR'
An alcohol
Properties of Esters
Saponification (Hydrolysis): an ester reacts with a hot aqueous base.
O
RCOR' + NaOH
Heat
H2O
An ester
O
CH3COCH2CH3 + NaOH
Ethyl Ethanoate
O
+
RCO-Na +
A sodium salt
H- OR'
An alcohol
O
- +
CH3CO-Na + CH3CH2OH
Sodium acetate
Ethanol
Amides
Amides
In an amide, the -OH group in the carboxyl group of a
carboxylic acid is replaced by an Amino group (-NH2).
O
CH3 — C—OH
O
CH3 — C — NH2
Formation of Amides
O
RCO H
A carboxylic acid
O
RC- OH H-NHR'
A carboxylic acid
An Amine
O
CH3 C- OH + HHNCH2 CH3
Acetic acid
Ethanamine
Heat
O
RCNHR' + H2O
An amide
O
CH3 C- NHCH2 CH3 + H2 O
N-ethylethanamide
Naming of Amides
Change the end of the name of the carboxylic acids from
“-oic acid” to “-amide”.
methanoic acid
O
H–C–NH2
methanamide (IUPAC)
O
propanoic acid
CH3–CH2–C–NH2
propanamide (IUPAC)
Naming of Amides
O
CH3–C–NH–CH3
N-methylethanamide
O
CH3–CH2–C–N(CH3)2
N,N-dimethylpropanamide
O
CH3–C–N(CH2CH3)2
N,N-diethylethanamide
Properties of Amides
Such as esters:
Hydrolysis in hot aqueous acid or base
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
6CO2 + 6H2O + energy
Photosynthesis
Respiration
C6H12O6 + 6O2
glucose
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.
Carbohydrates
1. Monosaccharide + H2O
2. Disaccharide + H2O
H+ or enzyme
H+ or enzyme
no hydrolysis
two monosaccharide units
+
3. Polysaccharide + many H2O
H+ or enzyme
many monosaccharide units
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
O
║
C─H
│
H─ C ─ OH
│
H─ C ─ OH
│
CH2OH
Cn(H2O)n
CnH2nOn
Monosaccharides - Aldose
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
O
║
C ─ H aldose
│
H─ C ─ OH
│
H─ C ─ OH
│
CH2OH
an aldotetrose
(Erythose)
Monosaccharides - Ketose
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)
CH2OH
│
C=O
ketose
│
H─ C ─ OH
│
H─ C ─ OH
│
H─ C ─ OH
│
CH2OH
“Keto-” + suffix
a ketohexose
(Fructose)
Some important Monosaccharides
Glucose (Dextrose)
(C6H12O6, aldohexose) – Blood sugar
• The most abundant monosaccharide
H O
C
H C OH
• 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.
HO C H
H C OH
H C OH
CH2OH
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.
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).
CH2OH
C O
HO C H
H C OH
H C OH
CH2OH
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.
H O
C
H C OH
HO C H
HO C H
H C OH
CH2OH
• Combines with glucose in lactose (a
disaccharide and a sugar in milk).
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.
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.
CHO
H
C
Convert to Fischer
Projection
OH
CH2 OH
3D
CHO
H
OH
CH2 OH
2D
Fischer Projections
1. Carbon with four different groups bonded to it.
2. The chiral carbon furthest from the carbonyl group (-CHO).
H
HO
H
H
CHO
* OH
* H
* OH
* OH
CH2 OH
D-Glucose
D - glucose
Naturally occurring enantiomer
CHO
CHO
CHO
CH2H
OH
CHO
H CHO
OH
O
H HO
OH
C=HO
OH CHO
H CHO
OH
O
* H
CHO
CHO
H
H
OH
O
HO HO
H
HH
H
HO
H
OHHO
H HH
O
H * OH
HO HO
HH * OH
H OH
H
HO
H
HO
H
HO
H
H H
OH
H CH
OH
HO
H
H HO
OH
H OH
* OH
H
H
H
OH
HO
H2
OH
CH
2
CH
CH
OH
H
D-Glucose
D-Galactose
CHOH
CHOH
2
2H
HOH
OH
H
OH
2 OH
2
D-Galactose
D-Fructose
CH
OH
CH
D-Glucose
D-Galactose
2
CH
OH
CH22
2
L - glucose
D-Glucose
D-Glucose
D-Galactose
D-Galactose
Cyclic Structure – Haworth Structure
1
1
Anomeric carbon
1
1
Alpha (α)
More stable form
1
Beta ()
Anomers
Cyclic Structure – Haworth Structure
CH2OH
CH2OH
O
O
OH 
1
1
OH
OH
OH 
OH
OH
OH
OH
-Glucose
-Glucose
CH2OH
O
OH
O
OH
1
OH
CH2OH
CH2OH
OH
OH
-Galactose
1
OH
O
OH
OH
OH
-Galactose
OH
OH
OH
CH2
1
CH
2 OH Structure – Haworth Structure
Cyclic
O
H HO
2
OH ( )
H
HO
H
1
2
Anomeric carbon
C=O
HO
H
H
OH
H 5 OH
CH2 OH
D -Fru ctose
 -D -Fructofuranose
( - D -Fructos e)
O
O
HOCH2
CH2 OH
CH2OH
1
O OH OH ( )
C=O
5
5
H HO
22
H
CH2 OH
1
H
HO
HOCH2
 - D -Fru ctofu ran os e
(- D -Fructose)
O
HOCH2
OH
2
H
H
OH
HO
H
-D-fructose
2
OH
H
H
OH
HO
CH2OH
H
-D-fructose
Cyclic Structure – Haworth Structure
O
O
1
OH

CH2OH
CH2OH
OH
1
OH

OH
OH
OH
-Glucose
OH
OH
-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 (contain β-glucose)
Mutarotation
Change in specific rotation that accompanies the equilibration
of α and  anomers in aqueous solution.
-D-glucose
Open-chain form
α-D-glucose
(acyclic)
64%
< 0.02%
36%
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)
Oxidation of Monosaccharides
OH
H O
C
H O
C
H C OH
HO C H
H C OH
H C OH
CH2OH
D - glucose
Aldonic acids
H C OH
+
2Cu2+
Benedict’s
Reagent (blue)
Oxidation
HO C H
H C OH
+ 2Cu+
(Brike red)
H C OH
CH2OH
D – gluconic acid
Reducing sugars: reduce another substance.
Oxidation of Monosaccharides
H O
C
CH2OH
C O
HO C H
Rearrangement
(Tautomerism)
H C OH
HO C H
H C OH
H C OH
H C OH
H C OH
CH2OH
CH2OH
D-fructose
(ketose)
D-glucose
(aldose)
Reduction of Monosaccharides
Alditols
Sugars alcohols: sweetners in many sugar-free (diet drinks & sugarless gum).
Problem: diarrhea and cataract
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
Disaccharides
The glycosidic bond joining the two rings can be alpha () or beta ().
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).
CH2OH
O
OH
O
O
+
1
OH
CH2OH
CH2OH
OH
OH
α-glucose
4
OH
OH
OH
OH
α-glucose
OH
CH2OH
 -1,4-glycosidic
bond
1
OH
OH
O
4
O
OH

+
OH
OH
- maltose
H2O
Disaccharides
Lactose:
•
•
•
•
Is a disaccharide of galactose and glucose.
Has a β -1,4-glycosidic bond (between β-galactose and α-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
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
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.
Artificial sweeteners
Aspartame:
It (sold as Equal) is hydrolyzed into
phenylalanine, which cannot be processed by
those individuals with the condition phenylketonuria.
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.
Artificial sweeteners
Sucralose:
It (sold as Splenda) has a very similar structure to sucrose.
Polysaccharides
• Polymers of many monosaccharides units.
Amylose (20%)
• Starch
(starch that stores glucose in plants such
as rice, potatoes, beans, and wheat).
Amylopectin (80%)
• Glycogen (animal starch in muscle and liver. It is
hydrolyzed in our cells and provides energy ).
• Cellulose (plant and wood structures).
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
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.
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.
Polysaccharides
Amylose, Amylopectin (starch)
H+ or α-amylase (enzyme in saliva)
Dextrins (6-8 glucose units)
Digestion process
H+ or α-amylase (enzyme in pancreas)
Maltose (2 glucose units)
H+ or α-maltase (enzyme)
Many α-D-glucose units
Respiration
C6H12O6 + 6O2
6CO2 + 6H2O + energy
glucose
Fermentation
C6H12O6
Yeast
2C2H5OH + CO2 + energy
Ethanol
Polysaccharides
Cellulose:
• Is a polysaccharide of glucose units in unbranched chains with
-1,4-glycosidic bonds (2200 glucose units).
• Has rigid structure (H-bond) and insoluble in water.
• Is the major structural material of wood & plants (cotton: 100%).
• Cannot be digested by humans because of the
-1,4-glycosidic bonds (needs an enzyme: -glycosidase).