Chapter 7.7: Hydration of Alkynes to Aldehydes and Ketones

Question 1

What is a type of isomerism involving keto (from ketone) and enol tautomers?

Answer 1

keto-enol tauteomerism

Question 2

Define keto-enol tautomerism

Answer 2

a type of isomerism involving keto (from ketone) and enol tautomers

Question 3

Describe the mechanism of hydroboration-oxidation of an alkyne with (sia)2BH

Answer 3

• Reaction of this sterically hindered dialkylborane with a terminal alkyne results in a single hydroboration and formation of an alkenylborane
o Treatment of an alkenylborane with hydrogen peroxide in aqueous sodium hydroxide gives a product that corresponds to hydration of an alkyne; that is, it corresponds to addition of H to one carbon of the triple bond and OH to the other

Question 4

Define tautomers

Answer 4

constitutional isomers in equilibrium with each other that differ in the location of a hydrogen atom and a double bond relative to a heteroatom

Question 5

Why is the hydroboration-oxidation of an alkyne with (sia)2BH Non-Markovnikov?

Answer 5

o The “antler” groups provide steric discrimination so the H atom adds to the more substituted C atom

Question 6

What is the stereoselectivity of hydroboration-oxidation of an alkyne w/o (sia)2BH

Answer 6

syn additon

Question 7

What are the reagents involved in the hydroboration-oxidation of an alkyne with (sia)2BH?

Answer 7

o 1. (sia)2BH

o 2. H2O2/HO-

Question 8

Describe the mechanism of acid-catalyzed hydration of an alkyne

Answer 8

 Step 1: Make a new bond between a nucleophile (pi bond) and an electrophile
 Step 2: Make a new bond 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

Question 9

What are the reagents involved in the acid-catalyzed hydration of an alkyne?

Answer 9

HgSo4/H2SO4

Question 10

Define enol

Answer 10

a compound containing a hydroxyl group bonded to a doubly bonded carbon atom

Question 11

What is the regiochemistry of hydroboration-oxidation of an alkyne with (sia)2BH?

Answer 11

Non-Markovnikov; boron adds to the less substituted carbon

Question 12

What is a compound containing a hydroxyl group bonded to a doubly bonded carbon atom?

Answer 12

enol

Question 13

Describe the mechanism of hydroboration-oxidation of an alkyne w/o (sia)2BH

Answer 13

o Borane adds to an internal alkyne producing a trialkenylborane
o The alkenyl group reacts further with borane to undergo a second hydroboration
o Treatment of an alkenylborane with hydrogen peroxide in aqueous sodium hydroxide gives a product that corresponds to hydration of an alkyne; that is, it corresponds to addition of H to one carbon of the triple bond and OH to the other

Question 14

What are constitutional isomers in equilibrium with each other that differ in the location of a hydrogen atom and a double bond relative to a heteroatom?

Answer 14

tautomers