Alkynes

By Ashley Lichkus

What are they? Alkynes are formally referred to as acetylenes or the acetylene series, which refer more specifically to the simplest member of a specific series. The basic definition of Alkynes is that they are hydrocarbons that contain at least one or more carbon-carbon triple bond. The formula that explains the Alkyne structure is CnH2n-2.

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This is a picture that shows the structure and set up of an alkyne.


What are they like?
Alkynes are among the hydrocarbon family, so they have a lot in common with the alkenes and alkanes. The Chemistry in comparison to the alkenes and alkynes are very similar in the aspect that they both are formed by elmination reactions. Another similarity is that alkynes typically undergo chemical reactions of the addition type. Being a part of the same family, alkynes and alkenes share many of the same attributes, but some things are different. Alkynes are very unstable but still are reactive and allow the reaction to take place accordingly. Hydrogen Deficiency
If there is a a triple bond(alkyne) the difference is four hydrogens compared to the alkane with the same number of carbons. We say that the Index of Hydrogen Deficiency is equal to the number of pairs of Hydrogens that must be taken away from the alkane to get the same molecular formula of the compound under investigation. Every Pi bond in the molecule increases the index by one. We can define the index of Hydrogen deficiency as the number of mols of H2 to saturate a structure.
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This is a chart that helps show the relationship between the different types of hydrocarbons. It helps depict the differences in the several types of formulas.


Reactions:
Syn Hydrogenation of An Alkyne

  1. There are two kinds of addition type reactions where a Pi bond is broken and atoms are added to the molecule. If the atoms are added on the same side of the molecule then the addition is said to be a "syn" addition. If the added atoms are added on opposite sides of the molecule then the addition is said to be an "anti" addition. Hydrogen atoms can be added to an alkyne on a one mole to one mole ratio to get an alkene where the Hydrogen atoms have been added on the same side of the molecule. This is called syn Hydrogenation.
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Sources:

http://hyperphysics.phy-astr.gsu.edu/HBASE/Organic/alkyne.html
http://members.aol.com/logan20/alkynes.html
http://ww2.bfafairfax.com/~pfeiffer/chemcom/alkanesenesines.JPG