A related reaction is dehydration,in which an alcohol is converted into an alkene and
water by the elimination of HXand XOH from adjacent carbon atoms. The dehydra-
tion of an alcohol to form an alkene can be considered the reverse of the hydration of an
alkene to form an alcohol (Section 27-17). Dehydration reactions are catalyzed by acids.
Such simple elimination reactions are relatively rare. Elimination reactions, however,
frequently occur as individual steps in more complex reaction sequences. Many more elim-
ination reactions are encountered in courses in organic chemistry.
POLYMERIZATION REACTIONS
A polymeris a large molecule that is a high-molecular-weight chain of small molecules.
The small molecules that are linked to form polymers are called monomers.Typical poly-
mers consist of hundreds or thousands of monomer units and have molecular weights up
to thousands or millions.
Polymerizationis the combination of many small molecules (monomers) to form
large molecules (polymers).Polymers are divided into two classes: natural and synthetic. Important biological mole-
cules such as proteins, nucleic acids, and polysaccharides (starches and the cellulose in
wood and cotton) are natural polymers. Natural rubber and natural fibers such as silk and
wool are also natural polymers. Familiar examples of synthetic polymers include plastics
such as polyethylene, Teflon, and Lucite (Plexiglas) and synthetic fibers such as nylon,
Orlon, and Dacron. In this section we will describe some processes by which polymers
are formed from organic compounds.
27-19
Concentrated sulfuric acid is an
excellent dehydrating agent. Here it
removes water from sucrose, a sugar
with the formula C 12 H 22 O 11.
Dehydration of sucrose produces
(mostly) carbon.27-19 Polymerization Reactions 1091The word fragment -mermeans “part.”
Recall that isomersare compounds that
are composed of the same (iso) parts
(mers). A monomeris a “single part”; a
large number of monomers combine to
form a polymer,“many parts.”