Alkynes

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. 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 — CH3 -------→ CH2 ═ CH2 -------→ 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. 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. Nomenclature What is IUPAC Nomenclature? IUPAC nomenclature is asystem of naming chemical compoundsand of describing the science of chemistry in general. It is developed and kept up to date under thesupport of theInternational Union of Pure and Applied Chemistry(IUPAC).

12. How to name an alkyne 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 │ │ CH2CH3 CH3

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 thelowest designated number. If it makes no differenceto the triple bond thenshift attention to the branched groups.

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

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

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

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

18. CH2=CH — C ≡ C — CH2— CH3 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. CH2=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. 1 – cyclobuten – 3 – yne Cl Br 3 – bromo – 6 – chloro – 1 – cyclohexen – 4 – yne Br Br C ≡ C — C = C — C ≡ C — C = CH2 Cl 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 compoundadds to amultiple bond. • In the case of addition reaction take place inALKYNES, one bond in thetriple bondis brokenin order toformnew bonds.

23. Alkyne Addition Reaction • Combustion • Halogenation • Hydrogenation • Hydrohalogenation • Hydration • Polymerization

24. Combustion Reaction Hydrocarbon + O2 ---------------→ CO2 + H2O Examples : 2 C2H2 + 5 02 -------→4 CO2 + 2 H2O C3H4 + 4O2 -------→ 3CO2 + 2H2O 2C4H6 + 11O2 -------→ 8CO2 + 6H2O

25. Halogenation Reaction Alkyne + Halogens -------→ Haloalkene -------→ Haloalkane Example: CH ≡ CH + Cl2 ------→ CHCl ═ CHCl + Cl2 ------→CHCl2 — CHCl2 Ehyne 1,1,2,2 - tetrachloroethane 1,2 - dichloroethene

26. Example: Br Br Br --------→ 2 Br2 + Br 1,1,2,2 – tetrabromocyclopentane CH3 CH3 F F │ │ │ │ CH ≡ C — C — CH3 + 2F2 -------→ 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 + 2H2 -------→ CH2 ═ CH2 -------→ CH3 — CH3 Ethyne Ethene Ethane

28. Example: : + --------→ 2H2 Cyclobutane Cyclobutyne

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

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

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

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

33. - Fin -