1. Alkynes
C ≡ C

2. Alkynes are……..
Aliphatic hydrocarbons with one triple bond between carbons
unsaturated hydrocarbons and are generally very reactive. Typical reactions involve the addition of hydrogens or halogens.
traditionally known as acetylenes or the acetylene series

3. General Formula
CnH2n-2

4. CH3 — CH3 -------→ CH2 ═ CH2 -------→ CH ≡ CH
Alkynes Preparation
The carbon-carbon triple bond of the alkynes is formed in the same way as a double bond of the alkenes, by the elimination of atoms or groups from two adjacent carbons.
CH3 — CH → CH2 ═ CH → CH ≡ CH
Alkene
Alkyne
Alkane

5. Alkynes Physical Properties
They are insoluble in water.
They are quite soluble in the usual organic solvents of low polarity (e.g. ligroin, ether, benzene, carbon tetrachloride, etc.).
They are less dense than water.
Their boiling points show the usual increase with increasing carbon number.
They are very nearly the same as the boiling points of alkanes or alkenes with the same carbon skeletons.

6. The carbon atoms in an ALKYNE bond are “sp” hybridized.
Structure:
The carbon atoms in an ALKYNE bond are “sp” hybridized.

8. Example:
HC ≡ CH
Ethyne

9. Example:
CH3—C ≡ CH
1 – Propyne

10. Example:
CH3 – C ≡ C – CH3
2 - Butyne

11. What is IUPAC Nomenclature?
IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. It is developed and kept up to date under the support of the International Union of Pure and Applied Chemistry (IUPAC).

12. How to name an alkyne 3 - heptyne CH2 — C ≡ C — CH2 CH2CH3 CH3
Step # 1
Determine the “ longest continuous chain “of carbons that have the triple bond between two of its carbons. The "longest continuous chain“ does not necessarily have to be straight.
3 - heptyne
CH2 — C ≡ C — CH2 │
CH3
CH2CH3

13. How to name an alkyne Step # 2
Number the carbons in the chain so that the triple bond would be between the carbons with the lowest designated number. If it makes no difference to the triple bond then shift attention to the branched groups.

14. 2,2,5 – trimethyl – 3 – hexyne Example : CH3 — CH — C ≡ C — C — CH3 │

15. Step # 3 How to name an alkyne
Identify the various branching groups attached to this continuous chain of carbons by name. If two or more alkyl group are attached to the chain alphabetize, then drop the “ane” suffix add “yne” to the name.

16. CH3 — CH2 — C — CH2 — C ≡ C — C — CH2 — CH3
Example :
CH3 — CH2 — C — CH2 — C ≡ C — C — CH2 — CH3 │
CH3
CH2 — CH3
CH3 — CH2
3,7 – diethyl – 3,7 – dimethyl – 4 - nonyne

17. 1 – cyclobutyne Br Cl CH2CH3 4 – ethyl – 4 – methyl – 1 – cyclopentyne
3 – bromo – 6 – chloro – 1,4 – cyclohexadiyne
CH2CH3
3HC
4 – ethyl – 4 – methyl – 1 – cyclopentyne

18. CH2 = CH — C ≡ C — CH2 — CH3 CH2 = CH — CH2 — CH2 — C ≡ CH
1 – hexen – 3 – yne
CH ≡ C — CH = CH — CH2 — CH3
3 – hexen – 1 – yne
CH2 = CH — CH2 — CH2 — C ≡ CH
1 – hexen – 5 – yne

19. HC ≡ C — CH = CH — C ≡ C — CH = CH2
1,5 – hexadien – 3 – yne
HC ≡ C — CH = CH — C ≡ CH
3 – hexen – 1,5 – diyne
HC ≡ C — CH = CH — C ≡ C — CH = CH2
1,5 – octadien – 3,7 – diyne

20. C ≡ C — C = C — C ≡ C — C = CH2 1 – cyclobuten – 3 – yne Br Cl Br Cl
3 – bromo – 6 – chloro – 1 – cyclohexen – 4 – yne
C ≡ C — C = C — C ≡ C — C = CH2 Br Cl
5,8 – dibromo – 2,6 – dichloro – 1,5 – octadien – 3,7 – diyne

21. Chemical Properties
Unlike alkanes, alkynes are unstable and very reactive. This gives rise to the intense heat (>3000 °C) of the acetylene flame used in welding.
The chemical behavior of the alkynes is characterized by their capacity of giving addition reactions, polymerization reactions and metallic derivates forming reactions. A great part of reactions are known as belonging to acetylene.

22. Addition Reaction Is a type of chemical reaction
in which a compound adds to
a multiple bond.
In the case of addition reaction
take place in ALKYNES, one
bond in the triple bond is
broken in order to form new
bonds.

23. Alkyne Addition Reaction
Combustion
Halogenation
Hydrogenation
Hydrohalogenation
Hydration
Polymerization

24. Hydrocarbon + O2 ---------------→ CO2 + H2O
Combustion Reaction
Hydrocarbon + O → CO2 + H2O
Examples :
2 C2H → 4 CO2 + 2 H2O
C3H O → 3CO H2O
2C4H O → 8CO H2O

25. Halogenation Reaction
Alkyne + Halogens → Haloalkene → Haloalkane
Example:
CH ≡ CH + Cl → CHCl ═ CHCl + Cl →CHCl2 — CHCl2
Ehyne
1,1,2,2 - tetrachloroethane
1,2 - dichloroethene

26. 1,1,2,2 – tetraflouro – 3,3 – dimethylbutane
Example: Br Br Br
2 Br2 → + Br
1,1,2,2 – tetrabromocyclopentane
CH3 F F
CH3 │ │ │ │
CH ≡ C — C — CH3 + 2F → HC — C — C —CH3 │ │ │ │
CH3 F F
CH3
1,1,2,2 – tetraflouro – 3,3 – dimethylbutane

27. Hydrogenation Reaction
Alkyne + Hydrogen → Alkene → Alkane
Example :
CH ≡ CH + 2H → CH2 ═ CH → CH3 — CH3
Ethyne
Ethene
Ethane

28. Example: : +
2H2 →
Cyclobutane
Cyclobutyne

29. Hydrohalogenation Example: Cl
Alkyne + Hydrogen halides → Haloalkene → Haloalkane
Example: Cl │
CH3 — C ≡ CH + 2HCl → CH3 — C — CH3 │ Cl
2, 2 - dichloropropane

30. Alkyne + H2O -------→ Aldehyde or Ketones
Hydration
Alkyne + H2O → Aldehyde or Ketones
Example: H O │ ║
CH ≡ CH + H2 — O → H — C — C — H │ H
Ethanal / (Acetaldehyde)

31. Example: 2 – Propanone (dimethylketone) O ║
CH3 — C ≡ CH + H2 — O → CH3 — C — CH3
2 – Propanone
(dimethylketone)

32. Example: → +
H2 — O ║ O
Cyclopentanone

33. - Fin -