2. Alkyne Nomenclature Common names (derivatives of acetylene)

3. Alkyne Nomenclature Replace “-ane” with “-yne” –Terminal alkynes1-butyne –Internal alkynes2-pentyne

4. Alkyne Nomenclature Replace “-ane” with “-yne” –Terminal alkynes1-butyne –Internal alkynes2-pentyne Alkyne is given lowest number

5. Alkyne Nomenclature When more than one triple bond use diene, triene....... If a double and a triple bond are present, number to give the lowest # If multiple functional groups are present, use both suffixes.

6. Alkyne Nomenclature Practice:

7. Alkyne Nomenclature Propargyl group is used in common names (similar to the allyl group)

8. Physical Properties All hydrocarbons have similar properties Alkynes similar to alkenes and alkanes –Less dense than water –Low polarity –Bp increase with MW Alkynes are more linear than alkenes Triple bond is more polarizable than C=C Stronger van der Waals interactions

9. Structure of Alkynes sp hybridized carbons –Bond angle is 180 o

10. Structure of Alkynes sp hybridized carbons –Overlap of p orbitals to form  bonds

11. Reaction Considerations Alkynes are e - rich (they are nucleopliles) Alkynes undergo electrophilic addition Rx Regioselective addition (Markovnikov’s Rule) The resulting alkene can also react

12. Priorities and Stability

13. Alkyne Reactions Hydrogen Halide addition Addition of Water Mercuric-ion-catalyzed hydration Hydroboration – oxydation Hydrogenation –Pd or Pt –Lindlars –Na or Li Acetylice ion

14. Acidity of H on an sp C The H attached to an sp hybridized C is acidic This explains some reactions of alkynes Alkynes