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.