3.35 Unsaturated Hydrocarbons
FIGURE 3.64
The bananas on the left were stored in
a special bag that absorbs ethene. The
bananas on the right were stored without
a bag.hydrocarbon is benzene, which has just one ring. Its structural formula is shown in theFigure3.65. Larger aromatic
hydrocarbons consist of two or more rings, which are joined together by bonds between their carbon atoms. The
name of aromatic hydrocarbons comes from their strong aroma, or scent. That’s why they are used in air fresheners
and mothballs. You can learn more about these interesting hydrocarbons at this URL:
http://www.youtube.com/watch?v=8gW7H0ReN5g
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5091Q:How many bonds does each carbon atom in benzene form?
A:Each carbon atom forms four covalent bonds. Carbon atoms always form four covalent bonds, regardless of the
atoms to which it bonds.
Alkynes
Unsaturated hydrocarbons that contain one or more triple bonds are calledalkynes. The names of specific alkynes
always end in–yneand have a prefix for the number of carbon atoms. The structural formula in theFigure3.66
represents the smallest alkyne, named ethyne, which has two carbon atoms and two hydrogen atoms (C 2 H 2 ). Ethyne
is also called acetylene. It is burned in acetylene torches, like the one pictured in theFigure3.67. The flame of an
acetylene torch is so hot that it can melt metal.
Alkynes may form straight or branched chains. They rarely occur in ring shapes. In fact, alkynes of all shapes are
relatively rare in nature.
Summary
- Unsaturated hydrocarbons are hydrocarbons with at least one double or triple bond between carbon atoms.
- Alkenes are unsaturated hydrocarbons with at least one double bond between carbon atoms.
- Aromatic hydrocarbons are unsaturated cyclic hydrocarbons with alternating single and double bonds between
carbon atoms. - Alkynes are unsaturated hydrocarbons with at least one triple bond between carbon atoms.