Alkynes

Question 1

Hydrohalogenation

Answer 1

Alkyne + HX –> trans alkene

trans alkene + HX –> geminal halide (geminal:gemini: twins)

Question 2

Halogenation

Answer 2

Alkyne + X2 –> trans alkene

trans alkene + X2 –> tetra halide

Question 3

Acid-Catalyzed Hydration

Answer 3

Alkyne + acid –> enol –> ketone

Question 4

Hydroboration-oxidation

Answer 4

Alkyne –> ketone

if TERMINAL Alkyne –> aldehyde

Question 5

Catalytic Hydrogenation (Reduction)

Answer 5

1. Synthesis of alkanes
2. Synthesis of cis-alkenes
3. Synthesis of trans-alkenes

Question 6

Synthesis of alkanes

Answer 6

+H2 and Pt in excess converts alkynes to alkanes

+2 moles H2 and Pd converts alkynes to alkanes

Question 7

Synthesis of cis-alkenes

Answer 7

Alkyne +H2 + Lindlar’s catalyst + Ni2B –> cis alkene

Question 8

Synthesis of trans-alkenes

Answer 8

Alkyne + H2 + Na/Li in NH3 in low temp –> trans alkene

Question 9

Lindlar’s Catalyst

Answer 9

P-2 or metallic Pd deposited in CaCO3

Question 10

Oxidation of Alkynes

Answer 10

1. Ozonolysis

2. Oxidation in KMnO4

Question 11

Ozonolysis

Answer 11

+ O3 –>

1. nonterminal alkynes : 2 carboxylic acids
2. terminal alkynes: 1 carboxylic acid and 1 carbonic acid

Question 12

Oxidation in KMnO4

Answer 12

+hot +basic +KMnO4 –> carboxylic acid + CO2

Question 13

Synthesis of Alkynes

Answer 13

1. Dehydrohalogenation of vicinal dihalides