The Organic Chemistry II Laboratory Course Chem 302, Spring 2008

43 Pages·2008·0.61 MB·English

The Organic Chemistry II Laboratory Course
Chem 302, Spring 2008
The experiments in this course have been chosen to illustrate important organic
reactions that we will discuss in lecture, and to utilize many of the skills that you
learned last semester.
Laboratory Safety
During this class we will work with a range of solvents, organic materials, acids,
and bases which could be harmful if you were to splash them into your eye or
onto your skin. For your own protection, we must require you to wear laboratory
goggles, which you can purchase at the campus store in Blanchard. Yes, they
are ugly and uncomfortable, but they are also very, very important. We also
strongly advise you to wear disposable gloves whenever appropriate. You may
not wear open sandals, but instead must wear closed–toe shoes. Furthermore,
we advise you wear clothing that fully covers your torso. (Shirts with spaghetti
straps and bare midriffs might be cute, but burns on your chest and stomach are
not).
On a related note, these lab handouts clearly indicate which chemicals should be
used in the hood because of possible inhalation hazards. Please read the labs
carefully and follow the directions. You will find that it is easiest, and safest, to do
everything you can in the hood.
Finally, it is extremely important to us that we be considerate of the environment.
Solvents may not under any circumstances be poured down the sink. Use the
appropriate designated waste bottles for halogenated and non–halogenated
waste. If you are unsure of which waste container to use, please ask your
instructor or TA.
Laboratory Reports
In place of lengthy laboratory reports, you will be asked to keep a careful record
of your work in a laboratory notebook containing carbon–copy duplicate pages
(just as you did last semester). The original copy will remain in your notebook for
reference later in the course, and the carbon copy will be turned in for grading.
Try to make your lab notebook as legible and organized as possible, but don’t
worry if you need to cross something out or change it—real science is
sometimes, in fact often, messy! Prepare your reports in ink.
Your laboratory notebook should include each of the following sections for each
and every lab, under clear sub–headings. The first three sections should be
completed before you come to lab and turned in to your instructor or teaching
assistant as a pre-lab before you begin the experiment. You should work on the
last three sections as you go along and finish as much of your write up as
possible before you leave.
________________________________________________________________ 1
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
(a) Title, date, and experiment number. Also, the name of your laboratory
partner.
(b) Reaction: A brief summary of the reaction(s) involved, including the
structures of the reactants, intermediates, and products, and a reasonable
mechanism. (You will probably have to look at your textbook and your
lecture notes and perhaps do some more extensive research).
(c) Methods: A brief summary of the process followed in the experiment. It
may be in the form of a flow–chart, or schematic outline, or some similarly
visually–accessible form. You need not repeat all of the details in the lab
handout, but you should make it clear that you have thought about the
experiment ahead of time. The intention here is that these additional
instructions will serve as an additional guide to your experimental work.
(d) Observations and Data: A careful record of what happened as you did the
experiment. Did a precipitate form, liquids separate into layers, or the color
of a solution change? At what stage of the experiment did this happen?
Include measurements, descriptions of the solutions, sketches of
chromatographic separations, and all spectra. You should also indicate
any changes you made in the experimental procedure.
(e) Discussion and Conclusions: Comment here on the overall level of
success and the ease (or otherwise) with which success was achieved.
Include any conclusions you have drawn about the purity or yield of your
material, and discuss what your results may have revealed about the
mechanism of the reaction.
(f) Answers to Questions: The questions are usually related to practical
elements of the experiments. You should look at the questions during the
laboratory sessions and talk over your ideas with your instructor or TA.
Reports are due at the beginning of the following week’s lab. If you submit a lab
report more than a week after the completion of an experiment, the grade you
receive will be halved for each week of delay. And, you must complete and
submit all 12 lab reports in order to pass this course.

________________________________________________________________ 2
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
Chemistry 302: Organic Chemistry II, Spring 2008
Week of Chapter and Topic Lab Experiment
Intro to class, review Diels-Alder
Jan 30th None
Ch 13 NMR
Ch 13 NMR
Feb 4th #1 The Diels–Alder Reaction
Ch 13 NMR
(set up Spectroscopy)
Ch 13 NMR
Ch 13, 14 NMR, Benzene
Feb 11th
Ch 14 Reactions of Benzene #2 Spectroscopy

Ch 14, 15 Reactions of substituted benzenes
Ch 15 Reactions of substituted benzenes
Feb 18th
Ch 15 Reactions of substituted benzenes #3 Tropylium

Ch 16 Reactions of carbonyls
Ch 16 Reactions of carbonyls
Feb 25th
Ch 16 Reactions of carbonyls #4 Nitration of Methyl Benzoate

review
Mar 3rd Exam #1
Ch 17 Aldehydes and Ketones #5 Banana Oil
Ch 17 Aldehydes and Ketones
Ch 17 Aldehydes and Ketones
Mar 10th #6 Preparation of a Naphthalene
Ch 17 Aldehydes and Ketones
Diimide
Ch 18 Intro to reactions at the alpha carbon
☺ Spring Break!!! Yeah!!! ☺
Ch 18 Substitutions at the alpha carbon
Mar 24th
Ch 18 Reactions at the alpha and beta carbons #7 The Wittig Reaction

Ch 18 Condensations
Review of carbonyls
Mar 31st
reveiw #8 Chemiluminesence

Exam #2
Ch 19 Reductions
Apr 7th
Ch 19 Oxidations #9 The Aldol Reaction

Ch 19 Oxidations
Ch 20 Amines
Apr 14th #10 The Grignard Reaction
Ch 20 Amines
(set up Ethanol lab)
Selected topics in biological chemistry
Selected topics in biological chemistry
Apr 21st #11 Biosynthesis and Distillation
Selected topics in biological chemistry
of Ethanol
Selected topics in biological chemistry
Exam #3
Apr 28th #12 Hydrolysis of Esters
Ch 29 Pericyclic Reactions
Check-out
Ch 29 Pericyclic Reactions
May 5th Last day of classes -----------------------------------------
________________________________________________________________ 3
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
#1: Diels–Alder Reaction of Anthracene with Maleic Anhydride

Purpose of the experiment
You will prepare the Diels–Alder adduct, sometimes called the cycloaddition
product, formed from the reaction of anthracene with maleic anhydride.

Introduction
As you will remember from last semester, the Diels-Alder reaction couples two
molecules, a conjugated diene and an alkene nicknamed a “dienophile”, via a
concerted [4+2] cycloaddtion reaction. In this reaction, three pi bonds (two on
the diene and one on the dienophile) are transformed into two new sigma bonds
and a new pi bond. The result is a new 6-membered ring containing a double
bond. In the molecular orbital description of this reaction, the HOMO of one
molecule reacts with the LUMO of the other in-phase to create the new bonds
through what is called a pericyclic reaction.

Today you will couple an electrophilic alkene, maleic anhydride, with the aromatic
compound anthracene (which will act as the diene) to create a new bridged
compound:
O
O
O
O O
O

What you will do
This experiment provides a straightforward introduction to organic synthesis. You
will prepare and isolate a Diels–Alder addition product by simply heating a
mixture of the two components—other than a reaction solvent, no other materials
are required.
________________________________________________________________ 4
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
Physical constants for the materials you will use or prepare
Material Mol. Wt. (g/mol) Mp (°C)
Anthracene 178 216–218
Maleic anhydride 98 54-56
m–Xylene 106 –48
Product 276 261–262

The experiment, step–by–step
Care! None of the reagents you will use in this experiment require special
precautions but you should get in the habit of handling all chemicals with respect.
Wear your laboratory glasses AT ALL TIMES. You will only use small amounts of
liquids and solids and these can be weighed and dispensed with little fuss.
Disposable gloves are available in the laboratory to use if you wish. Perform this
entire experiment in the hood.
1. Weigh out 1.0g of anthracene and 0.5g of maleic anhydride. Transfer both to
a clean, dry, 25mL round bottomed flask and add 10mL of m–xylene and a
boiling chip. Attach a reflux condenser—it is not necessary to connect water
hoses to the condenser for this experiment.
2. Arrange the apparatus on a sand bath for heating. For even heating it is best
if the flask is bedded down into the sand to around the same level as the
liquid contents. Turn up the controller to around 50% power and watch
(patiently) for bubbles to begin to form around the boiling chip—shortly after
the first bubbles form gentle refluxing (boiling) should commence. If boiling
has not commenced after 10 minutes then turn up the power slowly, and
incrementally, until it does so. Once you have reached this point let the
reaction boil gently for 30 minutes.
3. Turn off the power and carefully raise the reaction from the sand. Let the
mixture cool for at least 10 minutes and watch carefully—the reaction product
crystallizes as the mixture cools (avoid the temptation to cool the flask too
quickly, the best crystals are always obtained by slow cooling). Place the
cooled flask in a beaker of ice–water to complete the cooling and
crystallization process. Place 5mL of m-xylene in a small Erlenmeyer flask
and cool this on ice also.
4. Arrange the small Hirsch funnel and flask for suction filtration; you will need
to clamp the neck of the flask to keep it stable. The vacuum supply (yellow
taps on the hood) is quite strong and you will not need to have the tap fully
open (your Instructor or TA will show you how to set the vacuum at an
appropriate level). Inspect your reaction—if the crystals appear clumped
________________________________________________________________ 5
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
together, or adhere to the sides of the flask, gently poke around in the flask
with a clean spatula to free them. Swirl the flask and pour the contents into
the Hirsch funnel—try to be bold as otherwise you will simply drain the
solvent away and leave the crystals in the flask! Use a little of the extra cold
m–xylene to wash any remaining crystals out of the reaction flask, and use
the remaining cold m–xylene to wash the collected crystals on the filter
funnel. Let the crystals dry with the passage of air for a few minutes.
Disconnect the vacuum hose carefully and then shut off the vacuum. Spread
the crystals on a filter paper to complete the drying process.
5. Weigh the dried crystals and determine their melting point.
Cleaning up
Once you have recorded the yield and melting point of the final product you can
discard the material in the solid organic waste container. The filtrate from
collection of the crystals should be discarded in the non–chlorinated waste
solvent container. Rinse all of the glassware you have used with water and then
acetone, discarding the acetone washings in the non–chlorinated waste solvent
container.
Questions
1. The m–xylene reaction solvent, though it is not part of the chemical reaction,
plays two crucial roles in this experiment. Identify and explain both.
2. What are the structures of o–xylene, m–xylene and p–xylene? Why would p–
xylene have been a poor choice as a solvent for the procedure you followed
in this experiment? [Hint: what is the melting point of p–xylene?].
3. Why, in this particular case, is it not necessary to have cold water flowing
through the condenser in order for the solvent to condense and return to the
flask?
4. What is the purpose of washing the final product with cold xylene? [Hint:
think about the differing solubilities of the reactants and product in both hot
and cold xylene].

________________________________________________________________ 6
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
#2: Identification of an Unknown using Spectroscopy and
Spectrometry

Purpose of the experiment

You will use what you have learned about infrared spectroscopy, mass
spectrometry, and nuclear magnetic resonance spectroscopy to determine the
identity of an unknown compound.

Introduction

As you have seen in lecture, infrared spectroscopy (IR), mass spectrometry
(MS), and nuclear magnetic resonance (NMR) spectroscopy each provide
valuble information about the structure of a molecule. When considered together
they can often be used to determine the structure of a molecule about which little
or nothing else is known. Infrared spectroscopy provides information about the
types of functional groups present (or absent) in a molecule, though it tells little
about the way in which these groups are connected. Mass spectrometry
provides information about the mass of a molecule as well as the fragments it
forms when ionized. These fragments provide vital clues about the shape of the
molecule. Finally, NMR tells you about the chemical environment of all of the
hydrogen (1H NMR) or carbon (13C NMR) atoms in a molecule, allowing you to
connect the functional groups and fragments postulated from MS and IR properly
into a whole molecule.

What you will do

Each person will select an unknown compound of her own and obtain IR, 13C
NMR, 1H NMR, and mass spectra of it, using these to determine its structure.
You may work in groups of any size you like, but you must write up all the
unknowns for your group.

Advice regarding experimental or instrumental aspects

NMR: place one to two drops of unknown into an NMR tube and then add
solvent (CDCl ) up to the mark that is on the poster in the lab.
3

IR: Place one or two drops onto the sodium chloride cell then place the other cell
on top of the first, then run spectrum. Clean cells off with acetone.

________________________________________________________________ 7
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
GC/MS: Place one to two drops into 10 mL of pentane. Mix well before running
the spectrum. Please do not forget to clean the syringe when you are done with
the spectra.

Cleaning up
All NMR solvents must go in halogenated waste because of the CDCl . Acetone
3
rinsings from the IR should go in the acetone waste bottle. All GC/MS samples
will go in non halogenated waste, UNLESS your GC/MS shows that you have a
halogenated compound.

Questions

When proposing the structure of your unknown(s), include copies of all spectra
and discuss the following:

IR: What types of functional groups are present, and what band(s) at what
wavelength(s) leads you to that conclusion? What types of functional groups are
absent, and what band(s) at what wavelength(s) lead you to that conclusion?

MS: What is the mass of your whole molecule, and how does that match the
chemical formula of your molecule? How many degrees of unsaturation does
that correspond to? What fragments are formed, and how does that correpsond
to the molecule you have proposed?

1H NMR: How many non-equivalent protons are present on your molecule, and
how many peaks are present on your spectrum? Identify each peak on the
spectrum and explain how its chemical shift, integration, and splitting are
consistent with your proposed structure.

13C NMR: How many non-equivalent carbons are present in your molecule, and
how many peaks are present on your spectrum? Are any carbons missing a
peak, and if so, which and why? Identify each peak on the spectrum and explain
how its chemical shift is consistent with the 1H NMR spectrum and your proposed
structure.

________________________________________________________________ 8
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
#3:Preparation of Triphenylmethyl Fluoroborate and Tropylium
Iodide
Purpose of the experiment
To achieve a practical demonstration of the validity of Hückel’s 4n+2, π–electron
rule by preparing a non–benzenoid aromatic system.

Introduction

In this experiment you will prepare two relatively stable organic carbocations.
First you will prepare triphenylmethyl (a.k.a. “trityl”) carbocation from
triphenylmethanol. The acid protonates the –OH, making it a better leaving
group. When the water departs and is “soaked up” by acetic anhydride, what is
left behind is a stable tertiary carbon that is stabilized by resonance.

In the second step, the trityl carbocation will abstract a hydride from
cyclohepatriene, generating a tropylium carbocation (and triphenylmethane).
The tropylium carbocation is even more stable than the trityl carbocation and
thus can give up a hydride because it is aromatic.

The mechanisms for the reactions you will carry out are shown below:

What you will do
You will prepare sequentially two relatively stable organic carbocations. After
preparing the second carbocation you will demonstrate its ionic character by
confirming the presence of iodide with aqueous silver nitrate.
________________________________________________________________ 9
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)
Physical constants for the materials you will use or prepare
Material Mol. Wt. (g/mol) Mp (°C)
Triphenylmethanol 260 160–163
Tetrafluoroboric acid:dimethyl ether complex 88
Cycloheptatriene 92
Tropylium Iodide 218
The experiment, step–by–step
Care! Both acetic anhydride and tetrafluoroboric acid are corrosive and will case
painful burns if allowed to come into contact with your skin. Wear disposable
gloves when dispensing these materials.
Work in pairs for this experiment. Perform the entire experiment in the hood.
Part I. Preparation of the triphenylmethyl and tropylium carbocations.
1. Place a magnetic stirrer bar into a clean and dry 10ml round bottomed flask.
It is essential that the flask is absolutely clean and dry, the reaction will
otherwise likely fail. If you have any doubts scrub the flask in detergent and
water, rinse with water and then acetone and place in the drying oven for at
least 15 minutes.
2. Using the plastic graduated dropper provided transfer 3.5mL of acetic
anhydride to the flask and cool it on an ice bath for at least 10 minutes.
3. Using the syringe provided with the reagent transfer 0.25mL of
tetrafluoroboric acid:dimethyl ether complex to the flask and stir (gently) with
continued cooling.
4. Weigh out 0.39g of triphenylmethanol. Add the triphenylmethanol in one
batch to the stirred solution in the flask. Try to avoid having any of this solid
material stick to the neck of the flask and ensure that the solid and liquid mix
completely by adjusting the stirring rate and agitating the entire flask if
necessary. Remove the ice bath and stir for an additional 5 minutes.
5. Arrange a sand bath on top of the magnetic stirrer and bed your flask a little
way into the sand. Recommence stirring and heat the reaction very gently
(set the rotary temperature controller to around 30% for ten minutes and then
at 45% for five minutes) until you obtain a homogeneous red solution. It is
better to heat for a shorter time than a longer one so consult your Instructor
or TA for advice on when to stop. If you remove your solution from the heat,
it should stay the homogenous red color and not get cloudy. If it does, put it
back on the heat for a few more minutes.
6. Remove the heat source and allow the mixture to cool for 5 minutes. Using
the syringe provided add 0.2mL of cycloheptatriene to the stirred mixture. A
precipitate should soon begin to form. Continue to stir the suspension for a
________________________________________________________________ 10
Organic Chemistry II Laboratory Experiments, Spring 2008(Nunez, Browne, Hamilton, edited 1/08 JW)