SYNTHESIS

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SYNTHESIS
Make me a molecule
Rearrangement of atoms cleaving and making bonds
Aspirin
Tamiflu
Tagamet
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SYNTHESIS
Make me a molecule
Chemists make molecules they study the
properties of these molecules At heart of
their science is the molecule that is made.
? Roald
Hoffmann?
Constructing complex molecules is both an art and
a science which stretches the chemists knowledge
and insight, practical skills and imagination.
Synthesis is the bedrock on which the chemical
and pharmaceutical industries are built.
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In the beginning synthesis was unnecessary.
Chemistry was founded upon the study of those
materials which were available from natural
sources. Many of the materials we use today are
made by chemical synthesis. Most of the new
compounds made today are organic.
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Organic Chemistry
Organic Compounds
Most of the new compounds made today are organic,
that is, they are composed largely of carbon.
stable and versatile
unstable
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Product e.g. paint and pigment vitamin
synthetic fiber pesticide plastic
explosive pharmaceutical
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Synthesis involves breaking and making new
chemical bonds to create new chemical structures.
e.g. Aspirin
?In 400 B.C., the Greek physician Hippocrates
recommended chewing bark of the willlow tree to
alleviate the pain of childbirth and to treat eye
infections. It is known in ancient Egypt .
Salicin
active component
? Hydrolysis of salicin in aqueous acid gives
salicyl alcohol, which can be oxidized to
salicylic acid.
Salicyl alcohlol
? Salicylic acid proved to be an even more
effective pain reliever. Unfortunately, it causes
severe irritation of stomach.
Saliciylic acid
? In 1883, chemists at Bayer division of I. G.
Farben in Germany prepared aspirin. It proved to
be less irritating to the stomach than salicylic
acid and also more effective in relieving the
pain and inflammation of rheumatoid arthritis.
Acetylsalicylic acid (Asprin)
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Organic Synthesis

1. Carbon-Carbon Bond Formation
2. Functional Group Interconversion

Efficiency and selectivity are important
characteristics that have to be taken into
account. Efficiency yields, number of
steps Selectivity chemoselectivity,
regioselectivity, stereoselectivity
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Organic Synthesis

1. Carbon-Carbon Bond Formation
2. Functional Group Interconversion

Stereoselectivity
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Organic Synthesis

1. Carbon-Carbon Bond Formation
2. Functional Group Interconversion

Enantioselectivity
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???              
??????(Stereoisomers)
cis-1,2-dichloroethylene (bp 60 oC)
trans-1,2-dichloroethylene (bp 48 oC)
cis
trans
()-2-iodobutane (bp 119 oC)
(-)-2-iodobutane (bp 119 oC)
Chiral compounds
Enantiomer
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????? ??? (???)
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?????? (?????)
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Chiral Compounds
(-)-2-iodobutane (bp 119 oC)
()-2-iodobutane (bp 119 oC)
? D 15.9
? D -15.9
Enatiomers Optical isomers
They are optically active.
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Some Physical Properties of the Stereoisomers of
Tartaric Acid
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Louis Pasteur was born on December 27, 1822 in
Dole, in the region of Jura, France.
Louis Pasteur Chemist
Resolution of enantiomers in 1848
1822-1895
Twenty years later, J. H. vant Hoff and J.-A. Le
Bel independently explained the origins of
enantiomers based on the tetrahedral nature of
carbon bonding.
Chance favors only prepared mind.
-Louis Pasteur
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Resolution
diastereomeric salts ? seperation by selective
crystallization
or some other means
Once separated, acidification of the two
diastereomeric salts with strong acid gives pure
enantiomers and recover the chiral amine.