Alkyne Nomenclature

• Common names (derivatives of acetylene)

Alkyne Nomenclature

• Replace “-ane” with “-yne”– Terminal alkynes 1-

butyne

– Internal alkynes 2-pentyne

Alkyne Nomenclature

• Replace “-ane” with “-yne”– Terminal alkynes 1-butyne

– Internal alkynes 2-pentyne

• Alkyne is given lowest number

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.

Alkyne Nomenclature

• Practice:

Br

Br

Cl OH

Alkyne Nomenclature

• Propargyl group is used in common names (similar to the allyl group)

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

Structure of Alkynes

• sp hybridized carbons– Bond angle is 180o

Structure of Alkynes

• sp hybridized carbons–

Overlap of p orbitals to form bonds

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

Priorities and Stability

C

OOH NH2

highestpriority

lowestpriority

Alkyne Reactions

• Hydrogen Halide addition• Addition of Water• Mercuric-ion-catalyzed hydration• Hydroboration – oxydation• Hydrogenation

– Pd or Pt– Lindlars– Na or Li

• Acetylice ion

Acidity of H on an sp C• The H attached to an sp hybridized C is

acidic• This explains some reactions of alkynes

Alkynes