Friday, January 9, 2009

Alkynes - Conceptual Questions

1. What are alkynes?

2. Explain chain and position isomerisms in alkynes.

3. What is the reason for absence of geometrical isomerism in alkynes?

4. Explain the following processes of preparation of alkynes.

i. By dehydrohalogenation of dihalides or vicinal halides.
ii. By the action of zinc on tetrahalogen derivatives of alkanes (tetra halides)
iii. From acytelyne

5. Explain the follow processes of preparation of preparation of ethyne (acetylene).

i. Action of water on calcium carbide.
ii. electrolysis of acqueous solution of potassium salt of fumaric acid.
iii. synthesis from carbon and hydrogen.

6. What are physical properties of alkynes?
a. Physical state and smell
b. Boiling points
c. Solubility in water

7. Explain the following chemical reactions or properties of alkynes.

A. Addition reactions
i. Addition of halogens
ii. Addition of halogen acids
iii. Addition of hypohalous acids
iv. Addition of water
v. Addition of hydrogen cyanide
vi. Addition of hydrogen (hydrogenation)

B. Oxidation
i. Combustion
ii. Oxidation with alkaline potassium permanganate
iii. Oxidation with ozone

C. Polymerization reactions

D. Acidity of alkynes – Reactions with strong bases

8. Explain the acidic character of alkynes

9. Compare relative acidic strength of alkanes, alkenes and alkynes

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