Microscale Organic Experiments
Fourth Edition
HO3S
N N
N(CH3)2
A Laboratory Manual for
Organic Chemistry II
Chemistry 2040
Ray A. Gross, Jr., Ph.D.
Prince George’s Community College
Fall 2012
1
Preface
The experiments in this manual overlap the topics covered in the second edition
of “Organic Chemistry” by Janice G. Smith. They can be conducted in any sequence,
but the order of experiments parallels, as closely as possible, the order in which the
chapters of Smith’s text are covered in CHM 202, Organic Chemistry II. This manual is
the second-semester companion to “Techniques, Spectra and Reactions—A Laboratory
Manual for CHM 2010, Organic Chemistry I, To Accompany Smith’s, Organic
Chemistry, 3d Edition.”
The experiments are designed to minimize the use of chemicals and the
subsequent generation of waste while optimizing the use of microscale glassware. This
is now known as “Green Chemistry.” Instructors have the option of adding molecular
modeling or instrumental analysis of products to any of the experiments.
Like the earlier editions of this manual, this edition focuses on well-known and
important reactions and syntheses, such as the aldol condensation and Diels-Alder
reaction that students are likely to encounter in their follow-on studies in the biological
sciences. The discussions have been expanded to include mechanisms of the reactions
and related reactions. Some questions accompanying each experiment have been
changed. These questions are designed to test a student’s knowledge of the fundamental
principles covered during the second-semester organic course. Students who master this
content are well prepared for biochemistry, advanced chemistry and related courses.
This edition of this manual is not available in a printed form.
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ORGANIC LAB REPORT FORMAT
Serious students will keep a lab notebook and write up their results in the following
format.
Name R. Gross Lab Partner S. Sinex Expt # 2 Date 9/7/11
1. Purpose. To conduct a Diels-Alder reaction
A short, concise statement—not a complete sentence—of what you intend to accomplish.
2. Theory. Certain dienes react with double bonds (dieneophiles) to form new 6membered rings containing one double bond (cyclohexenes)—see Equation 1 below—
or triple bonds (the dieneophiles) to form new 6-membered rings containing two nonconjugated double bonds (1,4-cyclohexadienes)—see Equation 2 below. The reaction is
concerted and gives high yields. Diels and Alder shared the Nobel Prize for their
discovery of the reaction and the demonstration of its utility. The key features of the
reaction are: 1) it makes two new carbon-to-carbon single bonds, and 2) it makes 6membered rings from two acyclic compounds. In this experiment, both reactants are
part of ring systems—see Equation 3 below. The diene is cyclopentadiene and the
double bond reactant is maleic anhydride, a cyclic anhydride, containing a double bond.
The product of our reaction contains three rings—the cyclohexene—expected from a
Diels-Alder reaction—and a 5-membered ring made-up of the same 5 carbon atoms that
were present in the cyclopentadiene and a 5-membered ring made up of the same 5
atoms that were present in maleic anhydride. Thus, we make a tricyclo (3 rings in one
structure) compound. The Diels-Alder reaction belongs to a class of reactions called
cycloaddition reactions because the product always contains at least one ring (cyclo-)
and results from the addition of an -ene to a diene. The reaction proceeds by a cisaddition--substituents that are cis to each other in the original -ene reactant are also cis
in the adduct. In tricyclo compounds such as the one made in this experiment, the
principle of maximum overlap of π bonds leads to an endo-product. The endo-product
is produced even though the exo-product is thermodynamically more stable than the
endo-product. Thus, the reaction is the result of kinetic and not thermodynamic control.
In the Theory section, include principles that apply to the experiment. Include
information you can study for the final exam to refresh your memory about the nature,
scope and generalities of the experiment. Include enough information so that it will be
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unnecessary to refer to a lab manual or text—use these references to write the Theory
section.
3. Chemical Equations. [Note: Show the mechanism of the reaction!
Do not cut and paste (do your own work).
Equation 1
CO2Et
C
C
CO2Et
+
CO2Et
CO2Et
Equation 2
O
O
+
O
O
O
cyclopentadiene
O
maleic
anhydride
cis-norbornene-5,6-endodicarboxylic anhydride
Equation 3
4. Table of Reactants and Reagents.
Name or
Formula
Molecular
Weight
(g/mol)
Mass (g) or
Volume (mL)
Moles*
Melting or
Boiling pt
Other
Cyclopentadiene
66.10
0.20 mL =
0.16 g
0.0024
bp 41 oC
Dry
den 0.80
Maleic
anhydride
98.06
0.20 g
(powdered)
0.0020
mp 53 oC
Limiting
reagent
4
Ethyl
acetate
1 mL
Solvent
Ligroin
1 mL + wash
Solvent
* Moles = mass (g)/mol wt (g/mol). Since we need grams, if a liquid is used, we
find grams by using the density: vol (mL) x den (g/mL) = mass (g).
[This table clearly identifies what will be used and how much. The limiting
reagent must be specified in the “Other” box. The limiting reagent
governs how much product (i.e., the maximum amount) that can be made.
This amount is the theoretical yield in moles. (Consider two people, Jack
and Jill. Jack has 24 half-dollar coins and Jill has 20. The two are
allowed to contribute only equal amounts of half-dollars to make whole
dollars. How many dollars can they make? Answer 20 because of the
constraint that both must contribute half-dollars. Note that the number of
dollars that can be made depends on Jill who has the fewest number.) By
analogy, cyclopentadiene and maleic anhydride react according to
Equation 3, which shows that one molecule of cyclopentadiene reacts
with one molecule of maleic anhydride. Thus, the number of molecules of
product that can be made depends on which reactant has the fewest
number of molecules. We call this reactant the limiting reagent because it
limits the maximum amount of product to the number of molecules it
contributes to the reaction. We measure the number of molecules in
moles (one mole is 6.02 x 1023 molecules). The weight (mass) of 6.02 x
1023 molecules is the molecular weight of the compound in grams of the
compound per mole. Therefore, the compound, which contributes the
fewest moles to the reaction, is the limiting reagent. Thus, from the table,
we see immediately that maleic anhydride is the limiting reagent because
it contributes only 0.0020 moles and cyclopentadiene contributes 0.0024
moles. The number of moles of the limiting reagent is the maximum
number of moles of product that can be formed in this reaction.
In some reactions, the coefficients in the equation representing the
reaction are not all one. Consider 4A + B  2C. In a case such as this, A
must contribute 4 moles for every mole contributed by B, so finding the
limiting reagent requires an additional step. That is, you cannot see
directly from the table which reactant is the limiting reagent. If 0.24 moles
of A are used and 0.2 moles of B are used, it would require 4 x 0.2 moles
of A to react with 0.2 moles of B, and 4 x 0.24 = 0.96. Since only 0.24
moles of A are available, A is the limiting reagent because it will be all
used up before all of B reacts.] Most of our reactions are 1:1 but be alert
to reactions that are not.]
5. Diagram of the equipment setup or list of equipment.
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1. Small test tube
2. Pipette
3. Hirsch funnel
Normally, this section will include a free hand drawing of the equipment
setup. For example, if the reaction involved a distillation, you would
include a drawing of the apparatus. In several experiments, it is only
necessary to list the equipment. Do NOT draw pictures of commonly
used items such as test tubes and pipettes.
6. Procedure.
1. Maleic anhydride and cyclopentadiene were allowed to react in ethyl
acetate/ligroin--after several minutes, a white ppt formed.
2. The ppt was collected on a Hirsch funnel and allowed to dry on the filter
paper.
3. The white solid was weighed (0.295 g) and turned in.
As you and your partner conduct the experiment, you should record exactly
what you do in your notebook as you do it. This is not an essay on the
procedure. It is a short, concise summary of each step of the experiment,
consolidated to the extent possible.
7. Calculations.
1. Theoretical yield in grams. (Theoretical moles of product times its MW)
Because maleic anhydride is the limiting agent, 0.0020 moles of product
are possible because Equation 3 shows that 1 mol + 1 mol  1 mol.
0.0020 mol x 164.16 g/mol = 0.32832 g  0.33 g (only 2 significant figures)
This calculation tells you how many grams of product you could make if
every molecule of the limiting reagent reacted to give product.
2. Percent yield
Actual yield (grams)
Theoretical yield (grams)
x 100 = % Yield
0.295 grams x 100 = 89.3939%  89% (only 2 significant figures)
0.33 grams
This calculation is a measure of the overall efficiency of the reaction.
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8. Table of Product(s).
Name or
Formula
Molecular
Weight
(g/mol)
Mass (g)
or
Volume (mL)
Melting
or
Boiling
point
Properties
cis-norbornene5,6-endodicarboxylic
anhydride
164.16
0.295 g
mp 165 oC
White
plate-like
crystals
Other
9. Observations. The reaction occurred quickly and produced a high yield.
In the Observations section, you are free to express any thoughts that
you have about the experiment.
10. Conclusions. A diene and dieneophile reacted according to the Diels-Alder
reaction to produce a new 6-membered ring. The starting diene is locked in the scis conformation by the fact it is part of a 5-membered ring, so the reaction
occurred at room temperature. It was unnecessary to heat the reaction, because
the diene is already in the conformation to make the reaction go (i.e., the energy
of activation must be small). The three π bonds that took part in the reaction were
converted into two sigma (single bonds) and one new π bond (double bond). All
of the new bonds are part of the new 6-membered ring. No other bonds were
altered, thus a tricyclic product was made. The product is a derivative of the
common bicyclic compound, norbornene. Norbornene is a simple double bond
derivative of norbornane (bicyclo[2.2.1]heptane).
7
7
O
1
2
3
norbornane
bicyclo[2.2.1]heptane
6
4
O
O
5
O
norbornene
O
O
cis-norbornene5,6-endodicarboxylic anhydride
cis-norbornene5,6-exodicarboxylic anhydride
The high yield and stereospecificity of the reaction make it very valuable in the
synthesis of compounds containing 6-membered rings. The product of our
reaction contains an acid anhydride functional group, thus it will display two
carbonyl absorptions in its IR spectrum. The double bond will show an
absorption to the left of 3000 cm-1 in the IR. The endo-product is
thermodynamically less stable than the exo-product. See the structures above.
The completed report contains ten sections as numbered above and two
attachments, the data sheet and the answers to the 10 problems. Please number
your entries 1-10 as shown above. The entire report is worth 20 points—each
completed section is worth 1 point, and each question is worth 1 point.
Attachments
1. Original Data Sheet
2. Answers to the 10-Problem Set
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