Alkyne Reactions Flashcards
Addition of one mole of Br2 or Cl2 is ____ stereoselective.
anti
Addition of bromine and chlorine:
Anti addition of halogen to an alkyne gives an _________. Addition of a second ole of halogen gives a ________.
(E)-dihaloalkene, tetrahaloalkane
Addition of HX is _______.
regioselective
Addition of HX _____ follow Markovnikov’s rule.
does
Steps of mechanism for addition of HX to an alkyne.
Step 1: make a new bond between a nucleophile (pi bond) and an electrophile - add a proton
Step 2: make a new bond between a nucleophile and electrophile
Describe step 1 of addition of HBr to an alkyne: make a new bond between a nucleophile and an electrophile
Proton transfer from HBr to the alkyne gives a vinylic carbocation.
Describe step 2 of the addition of HBr to an alkyne: make a new bond between a nucleophile and an electrophile
Reaction of the vinylic carbocation (an electrophile) with bromide ion (a nucleophile) gives the vinylic bromoalkene
Describe step 1 for the addition of a second mole of HX:
The reaction of the electron pair of the remaining pi bond with HBr to form a carbocation
The sterically hindered (sia)2BH gives ________ reaction with 1-alkynes leading to ______.
regioselective, aldehydes
Alkynes react with water in the presence of H2SO4 and Hg(II) salts to give ______ via an ______ intermediate.
ketones, enol
Hydroboration of an internal alkyne is ____ stereoselective. Oxidation of the resulting __________ by H2O2/NaOH gives an ____ that is in equilibrium with a ________.
syn, trialkenylborane, enol, ketone
Hydroboration of a terminal alkyne using a hindered __________ followed by oxidation of the resulting ________ with H2O2/NaOH and the keto-enol tautomerism gives an _______.
dialkylborane, trialkenylborane, aldehyde
Acid-catalyzed addition of water in the presence of Hg(II) salts is ________.
regioselective
Acid-catalyzed hydration of alkynes is analogous to ___________.
oxymercuration of alkenes
For terminal alkenes, addition of water through acid catalyzed hydration ______ follow Markovnikov’s rule.
does
What are the steps of acid-catalyzed hydration of an alkyne?
Step 1: make a new bond between a nucleophile (pi bond) and an electrophile
Step 2: Make a new bon between a nucleophile and an electrophile
Step 3: take a proton away
Step 4: Keto-enol tautomerism
Step 5: Add a proton
Step 6 and 7: break a bond to give stable molecules or ions followed by keto-enol tautomerism
What are the reagents in acid catalyzed hydration of an alkyne?
HgSO4, H2SO4, H2O
What are the reagents in hydroboration-oxidation of an alkyne?
BH3 or (sia)2BH, H2O2, NaOH
Describe step 1 of acid-catalyzed hydration of an alkyne: make a new bond between a nucleophile and an electrophile
Attack of the C-C triple bond on the Hg2+ (an electrophile) gives a bridged mercurinium ion intermediate
Describe step 2 of acid-catalyzed hydration of an alkyne: make a new bond between a nucleophile and an electrophile
Attack of water (a nucleophile) on the bridged mercurinium ion intermediate (an electrophile) from the side opposite the bridge opens the three-membered ring.
Describe step 3 of acid-catalyzed hydration of an alkyne: take a proton away
Proton transfer to solvent gives an organomercury enol
Describe step 5 of acid-catalyzed hydration of an alkyne: add a proton
proton transfer to the carbonyl group of the ketone gives an oxonium ion
Describe step 6 and 7 of acid-catalyzed hydration of an alkyne: break a bond to give stable molecules and ions followed by keto-enol tautomerism
Loss of Hg2+ from the oxonium ion gives the enol form of the final product. Tautomerism of the enol gives a ketone
Reaction of an alkyne with two moles of H2 under moderate pressure in the presence of a transition metal catalyst at room temperature gives an ______.
alkane
