Ch' 11 Alkynes

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Ch. 11 Alkynes
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Structure and Bonding
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Structure and Bonding
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Naming Alkynes
1. The parent chain must contain the triple bond.
2. Change parent ending to -yne.
3. Give triple bond lowest possible .
6,6-dimethyl-2-heptyne
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What is the correct systematic name?
3-bromo-6-methyl-1-octyne
How many stereoisomers of this compound exist?
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Preparation of Alkynes
Alkynes can be prepared by double eliminations
geminal dihalide
vicinal dihalide
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Preparation of Alkynes
Examples-
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Reactions of Alkynes
Reactions of alkynes and alkenes are similar
can be E or Z
Breaking two p-bonds forms 4 new s-bonds
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Addition Reactions of Alkynes
1. Hydrogen halide addition (HCl, HBr, HI)-
produces geminal dihalides
Example-
geminal dihalide- two halogens located on the
same C atom
Mechanism?
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Addition Reactions of Alkynes
Another example-
Addition follows Markovnikovs rule
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Addition Reactions of Alkynes
2. Halogenation (Cl2, Br2) produces tetrahalides
Examples-
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Addition Reactions of Alkynes
3. H2O Addition produces ketones
Hg2 increases rate, but is not
required Markovnikovs rule is followed
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Addition Reactions of Alkynes
Mechanism is similar to alkene hydration Enol is
produced, tautomerizes to ketone
Enol form (less stable)
Keto form (more stable)
Tautomers constitutional isomers differing in
the placement of a double bond and a hydrogen
atom that are in equilibrium with one another
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Addition Reactions of Alkynes
4. Hydroboration-oxidation conversion of
alkynes to carbonyl compounds (aldhydes or
ketones)
Mechanism is similar to alkene hydroboration Term
inal alkynes produce aldehydes (anti-Markovnikov
addition) Enol is formed and undergoes
tautomerization
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III. Hydration of alkynes
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Reactions of Acetylide Anions
Terminal alkynes can be deprotonated to
produce strong nucleophiles
acetylide anion
NaNH2 and NaH are typical bases
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Reactions of Acetylide Anions
The acetylide ions formed may be used as
nucleophiles in SN2 reactions
Example-
Would this one work?
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Reactions of Acetylide Anions
The acetylide ions formed may be used as
nucleophiles in SN2 reactions
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Reactions of Acetylide Anions
2. Reaction with Epoxides strong nucleophile
reacts by SN2 pathway
Why does the attack occur at the top carbon
rather than the bottom one?
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Organic Synthesis
Many complex molecules require multiple steps to
prepare
Tamiflu
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Organic Synthesis
To work synthesis problems, you must- 1)
Understand the reactions 2) Be able to arrange
them in the correct order
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Organic Synthesis
How could this compound be synthesized
from acetylene?
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Organic Synthesis
How could this synthesis be carried out?
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