Alkyne Addition Reactions

Question 1

HX (HI, HBr, HCl) HX (HI, HBr, HCl)
—————————> —————————>
ROOR

Answer 1

For Terminal Alkynes
- forms Markovnikov addition product
- if peroxide ROOR is present, the Anti-Markovnikov product is formed

For Internal Alkynes
- In Asymmetrical Internal Alkynes, addition is not regioselective, so the two Halogens can add to either carbon forming a mixture of 2 products
- In Symmetrical Internal Alkynes, there will only be 1 product

Question 2

excess X2 (Br2, Cl2)
——————————>

Answer 2

Excess addition of Br2 or Cl2, results in tetrabromo or tetrachloro products

Question 3

H2
——————>
Pd, Pd/C, Pt

Answer 3

Turns Alkynes to an Alkane

Question 4

H2
—————————>
Lindlar’s Catalyst

Answer 4

Turns Alkynes to CIS/Z Alkanes

Question 5

Li/Na
———————>
NH3

Answer 5

Turns Alkynes to Trans/E Alkanes

Question 6

HgSO4
—————————>
H2SO4, H2O

Answer 6

Markovnikov addition of -OH and H

In terminal Alkynes, the product is an ENOL that tautomerizes to a Ketone

Question 7

1) 9-BBN, R2BH, THF
———————————>
2) H2O2, NaOH

Answer 7

Anti-Markovnikov addition of -OH and H that tautomerizes to an Aldehyde

Question 8

1) O3
————>
2) H2O

Answer 8

Terminal Alkyne Ozonolysis results in a Carboxylic Acid and CO2

Internal Alkyne Ozonolysis results in 2 molecules of Carboxylic Acid
- Unsymmetrical Internal Alkynes will produce 2 different Carboxylic Acids
- Symmetrical Internal Alkynes will produce the same Carboxylic Acid

Question 9

NaNH2/NaH
—————————>
Me or Alkyl Halide

Answer 9

A strong base such as NaNH2 or NaH can deprotonate a terminal Alkyne to form Acetylide Ion. An Acetylide Ion, being a strong nucleophile, can perform SN2 reaction on Methyl or Primary alkyl halide.

This reaction adds carbons to Alkyne.