Alkynes

Question 1

What are Alkynes?

Answer 1

Alkynes are unsaturated hydrocarbons containing carbon-carbon triple bond.

Question 2

What is the molecular formula for alkynes?

Answer 2

CnH(2n-2)

Question 3

What is a main source of alkyne?

Answer 3

The formation of acetylene from carbide:

Acetylene is produced from the reaction of carbon (coke) and calcium oxide at temp btw 1800 - 2100°C, producing carbide.

CaO(s) + 3C →CaC2 + CO

Carbide (CaC2) reacts with water to form ethyne.

CaC2 + 2H2O → C2H2 + Ca(OH)2

Question 4

Which functional group has the highest priority: Alkyl halides, Alkanes, Alkenes, Alkynes?

Answer 4

1. Alkenes
2. Alkynes
3. Alkanes
4. Alkyl halides

Question 5

What is the first member of the alkyne group?

Answer 5

Acetylene or ethyne.

Question 6

What acidity does Calcium carbide (CaC2) have

Answer 6

Calcium carbide is a strong base.

Question 7

What are the physical properties of alkynes?

Answer 7

1. Alkynes are soluble in organic solvents like propan-2-one and alcohols.
2. Boiling and melting points of unbranched alkynes increases down the group due to increasing strength in intermolecular Van Der Waal forces.
3. Acetylene (Ethyne) undergoes combustion in excess oxygen to produce a large amount of heat (2800°C), CO2 and water.
4. Alkynes are slightly more polar than alkenes and alkanes.
5. Alkynes have a slightly higher boiling and melting point than alkenes and alkanes.

Question 8

What is acidity?

Answer 8

Acidity is the measure of the ease at which an organic molecule releases a hydrogen atom previously bonded to it.

Question 9

What are the preparation of alkynes?

Answer 9

Alkynes can be prepared by the alkylation of acetylides in the presence of liquid ammonia

H₃C–C=–CNa + CH3I →(NH3)→ H3C–C=-C–CH3 + NaI