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: Cl Br OH Br

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 180 o

Structure of Alkynes • sp hybridized carbons – Overlap of p orbitals to form p 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

highest priority O C OH NH 2 lowest priority

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