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II continues the study of the hydrocarbons containing a
double bond. Topics addressed in this unit include structure and
bonding, reactions at the double bond and near the double bond,
polymers and polymerization, stereochemical aspects of alkenes,
and chemical analysis.
structure and nature of alkene bonding is covered in greater depth
here than in Alkenes I in order to introduce addition reactions
that occur at the point of unsaturation in a manner that is clear
and logical. These addition reactions, reactions that involve attack
by a good electrophile followed by a nucleophile, are diagrammed
in general using highly effective animations. After the general
diagram of the reaction is discussed, specific reactions are introduced
in such a manner as to capitalize on the general explanation.
The reactions studied are hydrogenation, hydration, hydrohalogenation,
hydrobromination with peroxides, halogenation, hydroxylation, oxidative
cleavage, halohydrin formation, carbene insertion, and peroxyacid
oxidation. Over four hundred screens are used in explanation of
these reactions. For example, the energy path generally accepted
in heterogeneous hydrogenation involving an alkene and hydrogen
gas in the presence of a solid catalyst is examined using potential
energy diagrams. Hydration via oxymercuration followed by demercuration
using the cyclic mercurinium ion is clearly diagrammed to explain
the lack of rearrangement, as opposed to the rearrangement expected
and realized when hydration with sulfuric acid occurs. The anti-Markovnikov
hydration using hydroboration/oxidation adds yet another interesting
aspect. Hydroxylation with permanganate, carbine insertion using
the Simmons-Smith reagent, and oxidative cleavage are a few more
of the reactions explained at lengh.
A small section introduces the topic of polymers and polymerization
and the methods by which polymers may be formed. Free-radical, cationic,
and anionic induced polymerization are addressed, with emphasis
placed on free-radical and cationic polymerization. Anion mechanisms
are addressed in a separate unit later in the course. The impact
of structure on polymer properties is briefly mentioned.
Animations are used to show the stereospecific products formed when
anti addition of halogens to alkenes to form both the cis and trans
structures occurs. Fisher projection diagrams are used, also.
Simple test tube tests are introduced as a way to quickly suggest
the presence of a double bond. The common tests producing a nice
color change such as bromination in the dark, the addition of basic
permanganate, and the addition of acid permanganate demonstrate
the way in which the reactions studied may have elegantly simple
applications. It is considered important for the student to realize
that reactions play a role in ways other than synthesis.
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