The Alkyne reference article from the English Wikipedia on 24-Apr-2004
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Alkyne

Helping orphans the way you would do it
Alkynes are hydrocarbons that have at least one triple bond between carbon atoms. The alkynes are traditionally known as acetylenes, though the name acetylene is also used to refer specifically to the simplest member of the series, known officially as ethyne.\r \r

Table of contents
1 Physical properties
2 Saturation
3 Examples
4 Reactions

Physical properties

\r Unlike an alkane an alkyne is unstable and very reactive. This gives rise to the intense heat of the acetylene flame used in welding. \r \r Alkynes also readily polymerise, like alkenes.\r \r

Saturation

\r Alkynes contain two units of unsaturation.\r \r

Synthesis

\r \r We start from a dihalogenized substance.\r \r 
\r

    H   H   H\r



    |   |   |\r



H - C - C - C - H\r



    |   |   |\r



    H   Cl  Cl\r
\r \r If we add NaOH to this, it will dissociate into Na+ and OH-. Na+ will not react, but OH- will pull off an electron from the substance.\r \r \r 2nd order elimination reaction. the 2 Cl will go to respect the tetravalent structure of the carbon. \r \r 
\r

              OH-               \r



             /                        Cl-\r



    H   Cl  H                    H         H-OH               H\r



    |   |   |                    |   |   |                    |     -\r



H - C - C - C - H   --->     H - C - C - C - H     --->   H - C - C - C - H\r



    |   |   |                    |   |   |                    |     -\r



    H   Cl  H                    H         H-OH               H  \r



             \\                        Cl- \r



              OH-                    \r
\r \r \r As before, 2nd order elimination reaction. the 2 Cl will go to respect the tetravalent structure of the carbon. \r \r 
\r

     OH-      OH-                  H-OH\r



       \\     /                            H-OH\r



    H   H   H                    H\r



    |   |   |                    |   |   |                      -\r



H - C - C - C - H   --->     H - C - C - C - H     --->   H - C - C - H\r



    |   |   |                    |   |   |                      -\r



    H   Cl  Cl                   H\r



                                            Cl- \r



                                    Cl-  \r


\r

\r


\r

Examples
\r
The simplest alkyne is ethyne (acetylene):\r
\r
image:ethyne.png\r
\r

Reactions
\r
\r

Terminal alkynes
\r

  1. terminal alkyne + strong base → anion of terminal alkyne\r

    • anion of terminal alkyne + methyl or primary alkyl halide → new carbon-carbon bond\r

    • anion of terminal alkyne + ketone → tetrahedral carbonyl addition compound (alkoxide)\r

      • alkoxide + aqueous acid → hydroxyalkyne\r

  2. terminal alkyne + dialkylborane + hydrogen peroxide & rarr; aldehyde\r

\r

Synthesis
\r

  1. alkene + bromine → dibromoalkane\r

\r

Addition
\r

  1. alkyne + 1bromine → (E)-dihaloalkene.\r

    • (E)-dihaloalkene + 1bromine → tetrahaloalkene\r

  2. alkyne + 2hydrogen halide → geminal dihaloalkane\r

\r

Reduction
\r

  1. alkyne + hydrogen gas + transition metal catalyst → alkane\r

  2. alkyne + hydrogen gas + Lindlar catalyst → cis alkene\r

  3. alkyne + hydrogen gas + alkali metal → trans alkene\r

\r

Other
\r

  1. alkyne + borane → trialkenylborane\r

  2. alkyne + water + mercury salt + acid catalyst → enol\r

\r