ORGANIC REACTIONS OF ALKYNES

Alkynes

• are sp hybridized

• linear - bond angle 180°

• 1 sigma and 2 pi bond (1 or single and 1 triple)

• triple bond ~ 1.21 A

react slower

most of the reactions discussed for alkenes also apply to alkynes, although alkynes usually _

bromination

the first bromine adds trans to the alkyne. It can be stopped by controlling the amount of Br₂ present, but a second addition is possible.

hydrogenation

ordinary Pt or Ni catalysts produce alkanes.

Lindlar’s reagent

a special Pd catalyst that causes only 1 H₂ in a syn addition to produce a cis-alkene

asymmetric alkynes

Markovnikov’s rule is followed for _, R-C≡C-H

hydration

requires an additional mercury (Hg²⁺) catalyst.

enol

the initial product (of hydration), rearranges rapidly to form a ketone