Organic Chemistry (Chapter 13: Alkynes)

Nomenclature of Alkynes

1. Number the carbons in a way that the carbon-carbon triple bond has the lowest priority numbers

2. Name the substituents and note their location

   • methyl group on carbon number 5

3. Name parent chain of the molecule including the location of the triple bond

   • hexane to hexyne

   • location of the triple bond starts on the first carbon

Special nomenclature example

• for this example it has a cyclic and a straight chain component

• when naming the longest carbon chain it is either EXCLUSIVELY the ring or the straight chain

  • NO mix and match

• since we are prioritizing the alkyne you want to name the longest carbon chain down in the straight chain

Priority: Highest to Lowest

Numbering begins closest to the highest priority group

The Reactivity of Alkynes

Relative Stabilities of Carbocations

Addition of H-X to an Alkyne

Addition of EXCESS H-X to an alkyne

In the presence of excess H-X the reaction proceeds to a geminal dihalide

Addition of H-X to an unsymmetrical internal alkyne

If the internal alkyne is SYMMETRICAL only one product is formed

The Addition of X2 to Alkynes

Proposed mechanism: analogous to the addition of X2 to alkenes (X₂=Cl₂, Br₂,I₂)

The Addition of water to an Alkyne

tautomerization is apart of the process

The Addition of Borane to an Alkyne (internal alkynes)

The hybridization-oxidation of internal alkynes occurs in an analogous way to the hydroboration-oxidation of alkenes:

The Addition of Borane to an Alkyne (terminal alkynes)

Two Methods to Hydrate an Alkyne

The Addition of Hydrogen to an Alkyne

The Addition of Hydrogen to an Alkyne (Alternative=lindlar catalyst)

How can you obtain a trans alkene from partial reduction of alkynes

Synthesis using Acetylide Ions

Synthesis (Example#1)

Synthesis (Example#2)