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Alkynes: Be sure to know these

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Alkynes: Be sure to know these & their mechanisms. Hydrohalogenation ... Steric hindrance around the leaving group causes 2 and 3 alkyl halides to ... – PowerPoint PPT presentation

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Title: Alkynes: Be sure to know these


1
Alkynes Be sure to know these their mechanisms
2
HydrohalogenationElectrophilic Addition of HX
3
HalogenationAddition of Halogen
4
HydrohalogenationElectrophilic Addition of HX
5
HydrohalogenationElectrophilic Addition of HX
6
HalogenationAddition of Halogen
7
HydrationElectrophilic Addition of Water
  • Internal alkynes undergo hydration with
    concentrated acid, whereas terminal alkynes
    require the presence of an additional Hg2
    catalystusually HgSO4to yield methyl ketones by
    Markovnikov addition of water.

8
HydrationElectrophilic Addition of Water
9
HydrationElectrophilic Addition of Water
10
HydroborationOxidation
Hydroborationoxidation is a two step reaction
sequence that converts an alkyne to a carbonyl
compound.
11
HydroborationOxidation
12
Introduction to Alkyne ReactionsAcetylide anions
13
Reactions of Acetylide Anions
14
Reactions of Acetylide Anions
  • Steric hindrance around the leaving group causes
    2 and 3 alkyl halides to undergo elimination
    by an E2 mechanism, as shown with
    2-bromo-2-methylpropane.
  • Nucleophilic substitution with acetylide anions
    forms new carbon-carbon bonds in high yield only
    with unhindered CH3X and 1 alkyl halides.

15
Reactions of Acetylide Anions
  • Acetylide anions are strong nucleophiles that
    open epoxide rings by an SN2 mechanism.
  • Backside attack occurs at the less substituted
    end of the epoxide.
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