http://www.ck12.org Chapter 25. Organic Chemistry
Alkynes
Analkyneis a hydrocarbon with one or more carbon-carbon triple covalent bonds. The simplest alkyne consists of
two carbon atoms and is called ethyne (Figure25.6).
FIGURE 25.6
Ethyne.The ethyne molecule is linear, and each carbon atom is sp hybridized. The general formula of an alkyne with one
triple bond is CnH 2 nā 2. Alkynes are also unsaturated hydrocarbons. As with alkenes, alkynes display structural
isomerism beginning with 1-butyne and 2-butyne. However, simple alkynes do not have geometric isomers because
each carbon involved in the triple bond is bound to only one additional group.
Optical Isomers
In addition to structural and geometric isomers, there is a third type of isomerism.Optical isomersare molecules
that are non-superimposable mirror images of each other. Most optical isomers have at least one atom, often carbon,
that is bonded to four different atoms or groups of atoms. Envision a mirror between the two molecules pictured
below (Figure25.7). The molecules are mirror images of one another, yet it is impossible to rotate one of the
molecules and superimpose it on top of the other. Your left and right hand are essentially mirror images of one
another, but they also cannot be superimposed.
FIGURE 25.7
The carbon atom is bonded to four
different atoms in a molecule of CHClBrF.
The molecules shown above are non-
superimposable mirror images, also
called optical isomers.Lesson Summary
- Organic chemistry is the chemistry of carbon-containing compounds. Carbon has the unique ability to make
long chains and ring structures, resulting in a virtually limitless number of organic compounds.