Alkyne Reactions

Question 1

Reduction via Catalytic Hydrogenation

Answer 1

H2, Pd/C
Turns alkyne to alkane bond
2x SYN addition

Question 2

Hydrogenation w/ Lindlar’s Catalyst

Answer 2

H2, Pd/CaCO3, quinoline
Partial reduction, produces CIS alkene product
SYN addition

Question 3

Hydrogenation w/ Sodium Metal in Ammonia

Answer 3

Na (s), NH3
Partial reduction, produces TRANS alkene product
Mechanism involves radicals: C* on the alkene bond, then Na* donates its electron to produce a lone pair on the C along with minus formal charge

Question 4

Hydrohalogenation

Answer 4

1 equiv. H-X
Adds X to more substituted Carbon and H to less substituted Carbon, forms alkene product
Excess H-X (slower step)
Adds second X to the same Carbon (geminal halogens), forms alkane product
Regiospecific Markovnikov addition

Question 5

Halogenation

Answer 5

1 equiv. X-X
First forms an epoxide with X, then the second X attacks (ANTI addition) and an alkene product is formed with each X on adjacent Carbons involved in the alkene
Excess X-X (slower step)
Adds one X to each Carbon involved in the alkene, alkane product forms

Question 6

Hydration w/ Catalytic Hg2+

Answer 6

HgSO4, H2SO4, H2O
Forms ketone/enol
Epoxide intermediate
Involves tautomerization

Question 7

Hydration w/ Hydroboration-Oxidation

Answer 7

1. R2BH 2. H2O2, NaOH
   Regiospecific Anti-Markovnikov addition
   Forms aldehyde alkane product