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9 Cards in this Set
- Front
- Back
Preparation of alkynes
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ELIMINATION OF DIHALIDES
1.loss of 2 HX to form an alkyne 2. Goes from alkene to alkyl dihalide(halogenation) to alkyne compound (USE OF KOH) 3. takes place through vinylic halide intermdeiate |
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Addition of HX
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* Alkyne compound
*HX *1st step give halogenated alkene, 2nd gives dihalogenated alkane *Markovnikov * |
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Addition of X2
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*Alkyne with X2
*1st step gives dihalogenated alkene, 2nd gives tetrehalogenated alkane *Trans stereochem *vinylic carbocation |
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Hydration of ALkynes via water catalyzed Hg(II) ion
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*Alkyne + H2SO4 in water catalyzed by HgSO4
*Gives ketone on an alkane *Markovnikov *enol intermediate (vinylic alcohol) *mixture of both possible ketones occurs on hydration of unsemtrical alkyne |
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Hydroboration-Oxidation of alkynes
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* alkyne + BH3 in THF
*if internal alkyne, Ketone if terminal alkyne, Aldehyde *Anti-markovnikov |
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reduction of alkynes
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* Alkyne + H2 w/ Pd/C catalyst or Lindlar catalyst
----->gives cis alkene product *Alkane(complete reduction) or alkene(lindlar catalyst) *can also use Alkali metals (Li) to reduce alkynes via an intermediate anion radical ----->gives trans product |
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Oxidative cleavage of alkynes
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* alkyne + KMnO4 or )3
*internal alkyne gives carboxylic acids terminal alkynes give CO2 + carboxylic acid |
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Acetylene
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H-C-triple bond-C-H
*can be deprotonated by the conjugate base of any acid with pKa above 25 |
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Alkylation of Acetylide anions
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*acetylide anion with alkyl halide
*forms new alkyne *1.acetylene alkylation gives terminal alkyne, 2. terminal alkyne alkylation gives internal alkyne. *Can only alkylate PRIMARY alkyl halides |