Alkyne Reactions:
Using the drawing pallet on the right, draw the structure of the major
organic product for the reaction shown below:
The reaction of an alkyne with two moles of HCl results in the
formation of a 1,1-dichloro group. The reaction involves the
intermediate generation of a vinyl halide, which adds the second mole
to give the final product. The regiochemistry of the reaction is
Markovnikov (the chlorines are bonded to the alkyne carbon which would
form the most stable carbocation).
Using the drawing pallet on the right, draw the structure of the major
organic product for the reaction shown below:
The reaction of an alkyne with BH3 in THF proceeds
through the formation of an organo-borane intermediate with the boron
bonded adjacent to the alkyne carbon which would form the
most stable carbocation (anti-Markovnikov addition).
Work-up with alkaline peroxide results in the formation of an
anti-Markovnikov enol> which rapidly reverts to the
corresponding carbonyl compound.
Using the drawing pallet on the right, draw the structure of the
major organic product for the reaction shown below:
Alkynes can be partially reduced to trans-alkenes using a
"dissolving metal reduction", in which the alkene is formed by a
radical mechanism in the presence of Li or Na metal, dissolving in
liquid ammonia. Please remember that this differs from the base sodium
amide, which is formed from sodium metal previously dissolved in liquid
ammonia.
Using the drawing pallet on the right, draw the structure of the
major organic product for the reaction shown below:
The addition of halogen to alkynes is a stepwise process involving a
"halonium" ion intermediate. The formation of this intermediate is
initiated through attack of halogen on the alkyne p-system, to form the cyclic halonium ion (i.e.,
bromonium or chloronium ion) and expel the halogen anion (i.e., bromide
or chloride). This intermediate is highly electrophilic and reacts
rapidly with the best nucleophile in the system; that is, the halide
anion expelled in the previous step. Attack by halide generates a vinyl
halide, which is an alkene and can undergo a second addition of
halogen. The final product of the reaction is therefore a
1,1,2,2-tetrahalide.
Using the drawing pallet on the right, draw the structure of the major
organic product for the reaction shown below:
The hydrolysis of an alkyne in the presence of Hg2+ ion
results in the formation of an enol in which the hydroxyl group
is bonded to the alkyne carbon which would form the most stable
carbocation (Markovnikov addition); the intermediate enol rapidly
reverts to give the corresponding carbonyl compound.
Using the drawing pallet on the right, draw the structure of the major
organic product for the reaction shown below:
The reaction of an alkyne with BH3 in THF proceeds through
the formation of an organo-borane intermediate with the boron bonded
adjacent to the alkyne carbon which would form the most
stable carbocation (anti-Markovnikov addition). Work-up with
alkaline peroxide results in the formation of an
anti-Markovnikov enol> which rapidly reverts to the
corresponding carbonyl compound.
Using the drawing pallet on the right, draw the structure of the
major organic product for the reaction shown below:
Terminal alkynes are slightly acidic and a powerful base such as
sodium amide (sodium previously dissolved in liquid ammonia) will react
with these compounds to give alkyne anions, which are powerful
nucleophiles. The most common reaction in which these nucleophiles are
utilized involves reaction with alkyl halides to displace the halogen
and form a new alkyne with a longer carbon chain . This mechanism is
shown in the similar reaction which is shown below.
Using the drawing pallet on the right, draw the structure of the
major organic product for the reaction shown below:
Lithium metal dissolving in liquid ammonia (a dissolving
metal reduction) will reduce an alkyne by a stepwise addition of
electrons to give the trans-alkene as product.
Using the drawing pallet on the right, draw the structure of the
major organic product for the reaction shown below:
Hydrogen gas in the presence of Pt or Pd, deposited on charcoal,
will completely reduce the alkyne to give the alkane.
Using the drawing pallet on the right, draw the structure of the
major organic product for the reaction shown below:
Hydrogen gas in the presence of Lindlar Catalyst, or Pt or Pd,
deposited on barium sulfate, will partially reduce the alkyne to give
the cis-alkene.
That is correct!
Sorry, that is not correct. You should modify your structures
and try again. If cis-trans- stereochemistry is required,
please make sure you have drawn the appropriate isomer using the "wedge
bonds".
Note: Stereochemistry is shown using the
"wedge" bond.
Click on the solid wedge to reverse orientation.
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