e-Assignment #3
Purpose & Results of the Free
Radical Chlorination of 1-Chlorobutane
Purpose:
The
purpose of this laboratory experiment is to determine the relative
reactivity of the different types of hydrogen atoms present on a
1-halogenated hydrocarbon. In particular, the experiment will
focus on the relative amount of each of the four dichlorinated products
produced from the free radical chlorination of 1-chlorobutane. By
comparison of each product's percent composition as well as its
statistical factor, the relative reactivity of the various hydrogen
atoms in the starting material will be determined.
The main
chemical concepts being investigated during the experiment is free
radical chlorination. During free radical chlorination, a
chlorine atom has the option of abstracting a primary hydrogen from the
methyl group or a secondary hydrogen from one of the methylene groups
to form a carbon radical on the carbon chain. Typically, a
secondary hydrogen will be more reactive and easier to abstract than a
primary hydrogen; however, this assumption is not valid in the case of
1-chlorobutane because the affect due to the presence of the chlorine
substituent is not known. Analysis of the dichlorinated products
will be carried out by gas chromatography and will hopefully provide
insight into the effect a chlorine and its location can have on the
relative reactivity of the hydrogen atoms in the molecule.
Results:
Conclusions:
It is apparent from the experiment’s results
that 1,3-dichlorobutane is more readily produced from the starting
material,
which indicates more reactive hydrogen atoms on the third carbon in
1-chlorobutane. In particular, the
1,3-dichlorobutane is 8 times more likely to be produced then the
1,1-dichlorobutane. Typically, primary hydrogen atoms are not as
reactive as secondary hydrogen atoms.
However, this trend is not followed explicitly due to the
chlorine
substituent on the starting material.
The presence of the chlorine substituent limits the amount of
1,1-dichlorbutane produced. Steric hindrance interferes with the
formation of a second C-Cl bond on the first carbon drastically.
It also plays a role in the formation of 1,2-dichlorobutane, but is
less likely to affect the formation of the C-Cl bond on the third and
fourth carbons. This reasoning would
indicate a higher percentage
of the 1,4-dichlorobutane product than the 1,2-dichlorobutane; however,
this is
not evident in the gas chromatogram.
Therefore, there must be another factor in determining the
relative
reactivity of the hydrogen atoms The last factor is most likely
the stability of
the carbon radical that forms during the free-radical process. A radical will be more stable when there are
more R groups attached to the carbon it is on.
The 1,4 product requires are radical to be present on the last
carbon
atom in the chain, which will be less stable than a radical present on
the
second carbon in the chain. This is why
the 1,2-dichlorobutane is more readily produced when compared to the
1,4-dichlorobutane.
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