Organic Chemistry - Carbohydrates

CARBOHYDRATES
CALAYCAY – CARINGAL – CASTILLO – JALOS – MADRID – PINEDA - ROXAS

Outline
I. Background about Biomolecules IV. Disaccharides
II. Definition of Carbohydrates • Glycoside Formation
III. Monosaccharides V. Polysaccharides
A. Structures • Structures
1. Fischer and Haworth
Projection
2. D and L Sugars
B. Reactions
1. Formation of ester and
ether
2. Oxidation
3. Glycoside Formation
4. Reduction of
monosaccharides
Biomolecules
Organic molecules naturally found in living
organisms which include:
• Proteins
• Lipids
• Nucleic acid
• Carbohydrates
most abundant
C, H, and O
energy source and structural component
Carbohydrates
Synthesized and metabolized by nearly all plants and animals
• source of readily available energy

• Why do we eat carbs instead of Fats?
History
• term arose because most sugars have Cn(H2O)
• “hydrates of carbon” or “carbohydrates”
“THE BROAD CLASS OF POLYHYDROXYLATED ALDEHYDES AND KETONES

COMMONLY CALLED SUGARS”
Carbohydrates
Classifications
• Simple
- composed of a simple sugar
• Complex
- made up of 2 or more sugars
Types of Carbohydrates (4)

Monosaccharides (1)
Disaccharides (2)
Oligosaccharides (2-10)
Polysaccharides (10+)
Monosaccharides
Definition
- can’t be converted into smaller sugars by
hydrolysis
Methods of Classifications (2)

• Ketone or Aldehyde
polyhydroxyaldehyde : Aldose (“aldo-”)
polyhydroxyketone : Ketose (“keto-”)
• Carbon Atoms Present
prefix tri-, tetr-, pent-, hex-, and hept-
• Numerous chirality
centers
• Emil Fischer (1891)

Fischer Projection
• Shows 3D open chain carbohydrates in 2D plane
Fischer Projection
• Do not give an accurate picture of the molecule’s true 3D
structure
Haworth Projection
• Used to depict
stereochemistry of sugars in
their cyclic form
• Does not accurately depict

conformation but can be
converted into chair form
Recall
Carbohydrates
- A biomolecule mainly found in living organisms
- Polyhydroxylated Aldehydes and Ketones
- Classified depending on structure
monosaccharides
ketose / aldose or based on # of C present
disaccharides
polysaccharides
Fischer to Haworth Conversion
Alpha and Beta Anomers
In a Haworth projection…
α (alpha) Anomer
- anomeric -OH is trans
with respect to the O of
the penultimate C
β (beta) Anomer
- anomeric OH is cis with
respect to the O of the
penultimate C
Fischer and Haworth Projection
Fischer Haworth
Depicts stereochemistry of sugars in
Shows 3D open chain molecules in 2D
cyclic form
plane
Do not give the accurate picture of the Do not accurately depict conformation
molecule’s true 3D structure
useful in identifying the position of –OH can be converted into chair form
group
D and L Sugars
Definition:
notation for designating carbohydrates
R = D : dextrorotatory
- naturally occurring
S = L : levorotatory
D and L Sugars
• d (+) and l (-) nomenclature designation
• Notations have no relation to the direction in which a given sugar rotates
- D and L sugars can still be dextrorotatory or levorotatory
• D and L sugars only indicates the position of –OH group at the highest
numbered chirality center
Reactivity of Functional Groups
Only contain hydroxyls and
carbonyl
REMEMBER:
• Alcohols can be converted into
esters and ethers
• Carbonyl compound can
reduced, oxidized and react with
nucleophiles
Monosaccharides: Reactions
1. Formation of Esters
• Esterification:
- Carbohydrate + Acid anhydride -[Base]-> Ester
2. Formation of Ethers
• Williamson Ether Synthesis
- Carbohydrate + Alkyl halide -[Base]-> Ether
3. Oxidation
• Aldoses -[O]-> Aldonic acids
*aldehydes -> carboxylic acids
Reducing vs Nonreducing Sugars
Reducing Nonreducing
ALL ALDOSES including some ketoses Majority of KETOSES and GLYCOSIDES
contains aldehyde group that can be acetal group is not hydrolyzed

reduced
3. Oxidation
• if dilute HNO3 (nitric acid) -> Aldaric acid (dicarboxylic acid)
• if only the -CH2OH end of the aldose is oxidized w/o affecting the
-CHO group -> Uronic acid (monocarboxylic acid)
4. Reduction
• Aldose or Ketose -[Hydride Reducing Agent]-> Alditol
Recall: ACETAL FORMATION
• NUCLEOPHILIC ADDITION:
Aldehyde/ Ketone + 2ROH –[Acid]-> Hemiacetal -> Acetal
5. Glycoside formation
• Carbohydrate + alcohol -[Acid]-> Glycoside
- anomeric –OH is replaced by an –OR group
Disaccharides
Definition;
can be hydrolyzed into 2 monosaccharides
Examples and Importance

- sucrose, lactose, and maltose
- common dietary component
Disaccharides
• Monosaccharide + alcohol -> Glycoside
- the anomeric –OH replaced by an –OR
if the alcohol is a sugar, the glycosidic product is a
disaccharide
Disaccharides: Glycosidic Linkage
• Glycosidic acetal bond is in between the anomeric carbon of a
sugar and an –OH group at any position on another
• ex: 1->4 link
Polysaccharides
• Relevance?
• complex carbohydrates in which up to thousands of
simple sugars are linked together through glycoside
bonds
• has only 1 anomeric –OH group at the end of a very long
chain
Polysaccharides: Structures
Cellulose
• major structural component of plants
• composed of several thousand d-glucose units linked by 1-> 4 -
β – glycoside bonds (like cellobiose)
Polysaccharides: Structures
Starch & Glycogen
• easily added to store energy or removed to provide energy
• composed of several thousand d-glucose units linked by 1-> 4-α-
glycoside bonds (like maltose)
• Amylose and Amylopectin
Summary
• What are Carbohydrates
• What are the type of Carbohydrates
• Constructing Fischer and Haworth
Projection
• Reaction of Monosaccharides
• Disaccharides and Glyosidic bonds
• Polysaccharide structures

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CARBOHYDRATES

CALAYCAY – CARINGAL – CASTILLO – JALOS – MADRID – PINEDA - ROXAS

• source of readily available energy

“THE BROAD CLASS OF POLYHYDROXYLATED ALDEHYDES AND KETONES

Types of Carbohydrates (4)

Methods of Classifications (2)

• Emil Fischer (1891)

• Does not accurately depict

contains aldehyde group that can be acetal group is not hydrolyzed

Examples and Importance

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