1. Chemistry

2. Alkynes

3. Session objectives 1. Preparation of alkynes by (a) Kolbe’s method
(b) dehydrohalogenation of vicinal dihalide
(c) dehydrohalogenation of geminal dihalide
2. Chemical reactions of alkyne
(a) Addition of halogen, hydrogenhalides.
(b) Ozonolysis
3. Confirmatory test for alkyne

4. General characteristics of alkynes
General formula CnH2n–2
sp hybridization
C–C bond length 1.2 A0
Shows chain and functional isomerism

5. Chain isomerism
Functional group isomerism

6. Preparation
Kolbe electrolysis

7. Dehydrohalogenation of vicinal dihalides
From gem dihalides

8. Miscellaneous methods
Miscellaneous methods From CaC2
Lime

9. Chemical properties
Addition Reactions
(i) Addition of hydrogen

10. Chemical properties Lindlar catalyst
(H2/Pd/BaSO4) partially reduces a disubstituted alkyne to a cis-alkene.
Trans-2-butene

11. Chemical properties
Addition of halogens
Addition of hydrogen halides

12. Mechanism

13. Addition of water

14. Hydroboration oxidation

15. Oxidation of alkynes

16. Ozonolysis of alkynes

17. Formation of alkynides

18. Formation of alkynides

19. Acidity of Alkynes
Ethyl anion
Acetylide anions
Vinyl anion

20. Acidity of Alkynes
sodium. acetylide

21. Acidity of Alkynes The order of boiling point among hydrocarbons is
alkynes > alkenes > alkanes.
These hydrocarbons also possess low dipole moment.
Acetylene having two hydrogen atoms is more acidic than a mono substituted acetylene.

22. Class exercise

23. Class exercise 1 How will you effect the following conversions?
Solution:
(a) (i) Cl2 + hn (ii) Wurtz reaction
(iii) Cl2 + hn (iv) alc. KOH, heat
(b) (i) HgSO4, H2SO4 (20%)
Hence, the answer is (c)

24. Class exercise 2
Write the structural formula of the main organic product.
Solution:
Hence, the answer is (b)

25. Solution

26. Class exercise 3
Give a chemical test to distinguish between 1-butyne and 2-butyne.
Solution:
1 butyne will give white ppt. with ammonical AgNO3.

27. Class exercise 4
A cylinder contains one of the following gases — propyne, propene, propane. What chemical test would you apply to identify the gases?
Solution:
AgNO3 (ammonical) is used for alkyne, alk. KMnO4, and heat is applied for alkene. No reaction takes place with propane with the above mentioned reagents.

28. Class exercise 5 Write the product of the following reaction.
Solution:
CH3CH2CHO

29. Class exercise 6
What reaction of an appropriate alkyne would lead to the following
product?
Solution:

30. Class exercise 7
An organic compound (A) having molecular formula when treated with NaNH2/ NH3 followed by reaction with n-propyl bromide yielded (B) . Compound (A) gives a ketone (C) when treated with acidified HgSO4. (B) on oxidation with hot alk. KMnO4 gives two isomeric acids (D) and (E). Deduce structures from (A) to (E).
Solution:

31. Class exercise 8 Write the correct product of the following reaction.
Solution:
Cl2CHCHO

32. Class exercise 9 Write the products of the following reaction.
C is CO2
D is C2H5CO2H E is H2O
F is HCOOH
G is C2H5COOH
Solution:

33. Class exercise 10
Write the intermediate steps of the following reaction
Solution:

34. Solution

35. Thank you