Term
| Like the __________ bond of an alkene, the __________ bonds of an alkyne are electron-rich, and they readily undergo __________ reactions. |
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Definition
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Term
| The bond energy of the alkyne triple bond is only about __________ more than the bond energy of an alkene double bond; this is the energy needed to break one of the __________ bonds of an alkyne. |
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Definition
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Term
When reagents cross the triple bonds of alkynes (or alkenes), the reaction converts a __________ bond and a __________ bond to two __________ bonds.
Since __________ bonds are generally stronger than __________ bonds, the reaction is usually exothermic. |
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Definition
1) Pi
2) Sigma
3) Sigma
4) Sigma
5) Pi |
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Term
| Alkynes have two __________ bonds, so up to __________ molecules can add across the triple bond, depending on the reagents and the conditions. |
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Definition
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Term
We must consider the possibility of a double addition whenever a reagent adds across the __________ __________ of an alkyne.
Some conditions may allow the reaction to stop after a __________ addition, while other conditions give the __________ addition. |
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Definition
1) Triple bond
2) Single
3) Double |
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Term
In the presence of a suitable catalyst, __________ adds to an alkyne, reducing it to an __________.
__________, __________, and __________ are the most common catalysts used for this reaction |
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Definition
1) Hydrogen
2) Alkane
3) Platinum
4) Palladium
5) Nickel |
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Term
__________ __________ takes place in two stages, with an (alkane/alkene) intermediate.
With efficient catalysts, it is usually impossible to stop the reaction at the __________ stage. |
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Definition
1) Catalytic hydrogenation
2) Alkene
3) Alkene |
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Term
Hydrogenation of an alkyne can be stopped at the __________ stage by using a "poisoned" (partially deactivated) catalyst made by treating a good catalyst with a compound that makes the catalyst less effective.
__________ __________ is a poisoned palladium catalyst composed of powdered __________ __________ coated with palladium, poisoned with __________. |
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Definition
1) Alkene
2) Lindlar's catalyst
3) Barium sulfate
4) Quinoline |
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Term
| Lindalar's catalyst is a poisoned __________ catalyst composed of powdered __________ __________ coated with palladium poisoned with __________. |
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Definition
1) Palladium
2) Barium sulfate
3) Quinoline |
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Term
| __________ __________ is a newer alternative to Lindlar's catalyst that is more easily made and often gives greater yields. |
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Definition
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Term
| The __________ __________ of alkynes is similar to the hydrogenation of alkenes, and both proceed with __________ stereochemistry. |
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Definition
1) Catalytic hydrogenation
2) Syn |
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Term
In catalytic hydrogenation, the face of a __________ bond of an alkyne contacts the solid __________ which weakens the __________ bond and allows two __________ atoms to add.
This simultaneously addition of two __________ atoms on the same face of the alkyne ensures __________ stereochemistry. |
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Definition
1) Pi
2) Catalyst
3) Pi
4) Hydrogen
5) Hydrogen
6) Syn |
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Term
| In an __________ alkyne, syn addition gives a cis product. |
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Definition
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Term
To form a trans alkene, two __________ must be added to the alkyne with __________ stereochemistry.
__________ metal with liquid __________ reduces alkynes with anti stereochemistry, so it is used to convert alkynes to __________ alkenes. |
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Definition
1) Hydrogen
2) Anti
3) Sodium
4) Ammonia
5) Trans |
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Term
| As __________ dissolves in liquid ammonia, it gives up electrons which produce a deep blue color; it is these solvated electrons that actually __________ the alkyne. |
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Definition
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Term
Metal-ammonia reduction proceeds by addition of an electron to the alkyne to form a radical __________, followed by protonation to give a __________ radical.
Protons are provided by the __________ solvent or by an __________ added as a cosolvent.
Addition of another electron, followed by another proton, gives the product. |
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Definition
1) Anion
2) Neutral
3) Ammonia
4) Alcohol |
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Term
*Metal-Ammonia Reduction of an Alkyne*
Step 1: An electron adds to the alkyne forming a __________ __________.
Step 2: The radical anion is protonated to give a __________.
Step 3: An electron adds to the radical, forming an __________.
Step 4: Protonation of the anion gives an __________. |
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Definition
1) Radical anion
2) Radical
3) Anion
4) Alkene |
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Term
The __________ stereochemistry of the sodium-ammonia reduction appears to result from the greater stability of the __________ radical in the __________ configuration, where the alkyl groups are farther apart.
An electron is added to the trans radical to give a trans __________ anion, which is quickly protonated to the __________ alkene. |
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Definition
1) Anti
2) Vinyl
3) Trans
4) Vinyl
5) Trans |
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Term
| Bromine and chlorine add to alkynes as they did to alkenes; the stereochemistry of addition may be either __________ or __________, and the products are often mixtures of __________ and __________ isomers. |
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Definition
1) Syn
2) Anti
3) Cis
4) Trans |
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Term
| If 1 mole of halogen adds to 1 mole of an alkyne, the product is a __________. |
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Definition
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Term
| If 2 moles of halogen add to 1 mole of an alkyne, a __________ product results. |
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Definition
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Term
| __________ __________ add across the triple bond of an alkyne in much the same way they add across the alkene double bond; their initial product is a __________ halide. |
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Definition
1) Hydrogen halides
2) Vinyl |
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Term
| When a __________ __________ adds to a (internal/terminal) alkyne, the product has the orientation predicted by __________ rule. |
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Definition
1) Hydrogen halide
2) Terminal
3) Markovnikov's |
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Term
The mechanism for the addition of hydrogen halides is similar to the mechanism which occurs in alkenes: the __________ __________ formed in the first step is more stable with the __________ charge on the more highly substituted carbon atom.
Attack by __________ ion completes the reaction. |
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Definition
1) Vinyl cation
2) Positive |
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Term
| When 2 moles of a hydrogen halide add to an alkyne, the second mole usually adds with the (same/different) orientation of the first; this leads to a __________ __________. |
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Definition
1) Same
2) Geminal dihalide |
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Term
__________ catalyze a free-radical chain reaction that adds __________ across the double bond of an alkene in the __________-__________ orientation.
A similar reaction occurs with alkynes, with __________ adding with __________-__________ orientation. |
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Definition
1) Peroxides
2) HBr
3) Anti-Markovnikov
4) HBr
5) Anti-Markovnikov |
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Term
Alkynes undergo acid-catalyzed addition of __________ across the triple bond in the presence of __________ ion as a catalyst.
A mixture of __________ __________ in aqueous __________ __________ is commonly used as the reagent. |
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Definition
1) Water
2) Mercuric
3) Mercuric sulfate
4) Sulfuric acid |
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Term
The __________ of alkynes is similar to that of alkenes, and the reaction also features __________ orientation.
The products are not the __________ we expect however: electrophilic addition of __________ ion gives a __________ cation, which reacts with water and loses a proton to give an _________ alcohol.
Under the acidic reaction conditions, mercury is replaced by hydrogen to give a vinyl alcohol known as an __________ (tend to be unstable and isomerize to the __________ form).
The __________ proton is lost, and a proton is regained at the __________ position, while the __________ bond shifts from the C=C position to the C=O position, a type of rapid equilibrium known as a __________. |
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Definition
1) Hydration
2) Markovnikov
3) Alcohols
4) Mercuric
5) Vinyl
6) Organomercurial
7) Enol
8) Ketone
9) Hydroxyl
10) Methyl
11) Pi
12) Tautomerism |
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Term
| In acidic solution, __________-__________ __________ takes place by addition of a proton to the adjacent carbon atom, followed by loss of the __________ proton from oxygen. |
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Definition
1) Keto-enol tautomerism
2) Hydroxyl |
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Term
*Acid-Catalyzed Keto-Enol Tautomerism*
Step 1: Addition of a proton at the __________ group.
Step 2: Loss of the __________ proton. |
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Definition
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Term
The same hydroboration-oxidation reaction takes place with alkenes also occurs in alkynes, with the exception that a hindered __________ must be used to prevent the addition of two molecules of __________ across the triple bond.
__________ adds to the triple bond only once to give a vinylborane.
In a (internal/terminal) alkyne, the boron atom bonds to the terminal carbon atom.
Oxidation of the vinylborane (using hydrogen peroxide) gives a __________ __________ (enol) resulting from __________-__________ addition of water across the triple bond.
The enol quickly __________ to its more stable carbonyl (keto) form.
In the case of a terminal alkyne, the keto product is an __________.
This sequence is an excellent method for converting terminal alkynes to __________. |
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Definition
1) Dialkylborane
2) Borane
3) Disiamylborane
4) Internal
5) Vinyl alcohol
6) Anti-Markovnikov
7) Tautomerizes
8) Aldehyde
9) Aldehydes |
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Term
Under __________ conditions, the keto-enol tautoemerism operates through a different mechanism than it does with acids:
In base, the proton is first removed from its old position in the __________ group and then replaced with a __________.
In acid, the proton was first added on the __________, and then removed by the __________ group. |
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Definition
1) Basic
2) Hydroxyl
3) Carbon
4) Carbon
5) Hydroxyl |
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Term
*Base-Catalyzed Keto-Enol Tautomerism*
Step 1: Loss of the __________ proton.
Step 2: __________ on the adjacent carbon atom. |
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Definition
1) Hydroxyl
2) Reprotonation |
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