Chem 08LA Lab Manual
Winter 2020
Chem 08LA
Organic Chemistry
Laboratory Manual
UC Riverside
Winter 2020
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Chem 08LA Lab Manual
Winter 2020
CHEMISTRY 08LABC LABORATORY POLICIES
on
SAFETY AND PERSONAL PROTECTIVE EQUIPMENT (PPE)
INSTRUCTOR
Professor Richard Hooley
Chemical Sciences 1, Room 444
(951)-827-4924 email: richard.hooley@ucr.edu
ACADEMIC COORDINATOR
Dr. Rena Hayashi
Science Laboratories 1, Room 103
(951)-827-3143, email: rena.hayashi@ucr.edu
This document establishes the safety policies for students enrolled in the Organic Chemistry teaching
laboratory (Chem 08LA, 08LB and 08LC). Students failing to comply with all safety rules herein as well
as any safety direction from any course staff member (TA, Academic Coordinator, or the Instructors) are
subject to a variety of sanctions, including dismissal from a particular laboratory session (resulting in a
zero grade for the experiment), and may be subject to dismissal from the course.
Personal Protective Equipment
a)
Wear safety goggles at all times while in the laboratory.
b)
Lab coats must be worn at all time while in the laboratory.
c)
No exposed legs or arms are permitted in the laboratory – shorts or skirts may never be worn.
d)
No sandals, open-toed or perforated shoes, or shoes with absorbent soles are allowed in the
laboratory.
e)
Nitrile gloves are supplied, and must be worn while performing all transformations. It should be
noted that while gloves provide a barrier to chemicals coming into contact with skin, they do not
provide perfect protection. Nitrile gloves are permeable to a number of organic liquids (especially
chlorinated solvents and dimethylsulfoxide). If you spill chemicals on your gloves, remove and
replace the gloves immediately. Good practices are to a) minimize spillage and other modes of
contact with chemicals, and b) immediately wash your hands with soap and water after contact
with any harmful reagent or solvent.
General Safety
a)
No hats, scarves, neckties, long unrestrained hair, or overly loose clothing are permitted.
b)
Cellular phones may never be used in this laboratory. Make certain that your phone is
turned off before entering. If you use a cellphone during lab, it will be confiscated by your
TA for the duration of the lab period.
c)
No eating, drinking, or smoking in the laboratory. Food and drinks may never be present. This
includes all visible water bottles or mugs, containers of water or flavored drinks, containers of ice
intended for consumption, etc. A food or drink container may be present only if it is empty /
unopened and out of sight, such as inside a backpack.
d)
Bicycles, skateboards, in-line skates, roller-skates, and unicycles are not allowed in the
laboratory. Their use is also not allowed inside the Science Laboratories building. If skateboards
are brought into the building, they may not be placed on the floor.
Medical Conditions
a)
You should not work in the laboratory if you are pregnant or you might be pregnant. Contact
course staff in this situation. In addition, notify the Academic Coordinator if you have any other
medical conditions (diabetes, allergies, etc.) that may require special precautions to be taken.
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Fire and Emergency
a)
Make sure to know the locations of safety showers, eyewash fountains, fire extinguishers,
emergency telephones, fire alarms and all exits. These are clearly marked in the laboratory.
b)
FIRE: Immediately notify the supervising TA. A fire confined to a small flask or container can
usually be extinguished by covering the flask with a large nonflammable container (e.g. beaker).
Only attempt this is the fire can be easily contained: otherwise pull the fire alarm and exit the
building. Go to the designated assembly area and do not use the elevator.
If a person's clothing is on fire, use the safety shower to put out the flames. If this is not possible,
douse the person with water, cover them with a fire resistant coat and roll the person on the floor.
c)
INJURY: Immediately report ANY injury to a TA, no matter how minor. The TA will initiate
emergency procedures and arrange transportation to a medical facility.
If you are a member of the Campus Student Health Plan, then during normal business hours go
to the Campus Health Center (for current business hours go to www.campushealth.ucr.edu).
After hours until 9 pm: go to Riverside Medical Clinic Urgent Care.
All other times: Riverside Community Hospital.
If you are NOT a member of the Campus Student Health Plan, then during normal business hours
go to the Campus Health Center and inform them that you are not on the health plan but were
injured while on campus. At all other times, obtain medical treatment through your personal health
insurance coverage (i.e. HMO, PPO).
d)
CHEMICAL SPILL: Chemical contact with eyes and skin must be washed immediately with
water for at least 15 minutes (use the eye wash/safety shower). Remove contaminated clothing
and immediately report the incident to a TA.
Other Laboratory Rules
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Do not put lab chemicals in your drawer, unless specifically instructed to do so by your TA.
NO ignition sources (matches, lighters, etc) are allowed in the laboratory.
There is absolutely no smoking allowed anywhere at any time in the Sciences Laboratories
building.
Do not pour chemicals into the sink or dispose into the trash: use the proper waste containers.
Dispose of chemical waste in the specified containers - some chemicals are dangerous if mixed.
Do not use unlabeled chemicals, and if you find any, report this to your TA
Do not drink from lab faucets or use the ice from lab ice machines to chill food. The water may
not be safe to drink.
NEVER mix chemical reagents unless instructed to do so by your TA as part of your lab
procedure.
NEVER taste or smell chemicals.
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LABORATORY PROCEDURES - LAB REPORTS, FINAL EXAM AND GRADING
The final grade for this class will be dependent on your scores in both the laboratory and the final exam.
Laboratory Reports (240 points): These will count for 50% of your overall score. Each lab report is
worth 30 pts, and you will gain a majority of the lab score points for submitting a completed lab report.
The final set of points are given for correctness in your report. You will not pass the class without
attending all labs and submitting a completed lab report for each lab. Excused absences will be
considered, but you must provide documentation (see Lab Rules section).
Final Exam (240 points): The final exam is on the Friday evening of week 10, and will consist of
40 multiple choice questions. This exam will be the major determining factor for your grade, counting
for 50% of your total score in the class. At the end of each lab in this book, there is a section containing
10 multiple choice questions based on that lab. These questions will not be graded - your TA will give
you the answers to these questions. There are therefore 80 multiple choice questions (and answers!) in
the book - your final exam will consist of 40 of these questions.
NOTE - you will be given the answers to the questions in the book, but I will change the letter
entries (A-E) for the exam. The questions/answers will be identical, but the letter of the correct
answer will change. So you need to know the answer to the question, not just memorize the correct
letter response!
You will not be allowed to bring anything to the final exam - you have the questions and the answers, so
make sure you study them well.
FORMAT FOR LABORATORY NOTEBOOK REPORTS (Read Zubrick p11-26)
Keeping an accurate laboratory notebook is essential to your success in this class. Some guidelines are
given below:
a) The laboratory notebook must not be loose leaf or spiral bound. Lab notebooks are available from the
campus bookstore and are designed so that they permanently contain the original pages of your Prelab
and Postlab reports.
b) Use permanent blue or black ink only (ballpoint pen, NO red ink!).
c) Other textbooks, lab manuals, loose sheets of paper, tablets or cellphones are not allowed in the
laboratory. The complete outline of procedures must be written in your laboratory notebook prior to
performing the experiment.
d) Copies of your lab notebook pages are required for grading. The assigned notebooks are designed
so that the carbon copies can be removed and handed in to your TA.
e) Your TA may periodically inspect your notebook.
YOUR LAB REPORT CONSISTS OF THREE (3) PARTS - HAND IN PARTS I AND II
Part I - Prelab Report. A copy of your lab notebook pages containing the lab writeup and answers to any
prelab questions. This is due at the start of each experiment.
Part II - Postlab Report. This is in two parts - a description of results, consisting of a copy of your
notebook pages containing observations noted during the lab experiment, and an analysis of the
experiment, consisting of critical analysis of your results and learning outcomes from the experiment.
Part III - Exam Questions. At the end of each experiment, there are 10 multiple choice questions based
on that experiment. You are responsible for doing the lab exam questions and understanding
the answers. You will be given the letter answers for the questions, and they are not to be handed
in. A selection of these questions will make up the final exam.
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I. PRELAB REPORT (40% of the report grade)
There will be two types of prelab report in this quarter’s laboratory. Experiments 2-4 will employ
a “flipped” lab, whereby the bulk of the prelab requirements will be to watch a video on techniques
in organic chemistry and answer pre-lab questions. Experiments 5, 6, 7 and 8 follow the “classic”
prelab format that will continue in Chem 008B and 008C. Note that Expt 1 is a dry lab, with no
prelab requirement.
PRELAB REPORT (Expts 2-5)
The pre-lab activities for Expts 2-5 consist of viewing the Technique Video (posted on iLearn), and writing
a pre-lab report that consists of answering questions from the video and writing a procedure for the
upcoming experiment.
Prelab Quiz: Your TA will give you a pre-lab quiz on the topics in the video and in the relevant Zubrick
reading before your lab starts. This will be worth 4 points of your lab score.
The initial part of your lab report must be written in your laboratory notebook. A copy of the original pages
of this report will be collected prior to the experiment and will be returned to you after the whole lab is
graded. It will consist of:
a) Your name, lab section and the name of your TA (on each page).
b) The title and number of the experiment.
c) Objectives. This should include hypotheses about the outcome of the lab, which you will test by
experiment. It is your responsibility to propose what you expect to determine from each
experiment.
d) Outline of procedure. This must be sufficiently detailed to allow you to perform the experiment. Make
sure you note any necessary safety precautions.
e) Chemical List (see individual experiment for specifics). Look up molecular masses and calculate the
material amount in moles (if appropriate), boiling/melting points (bp/mp) and density (if appropriate).
f) Safety questions. Read the MSDS forms (on iLearn) for the chemicals used in that week’s experiment.
The questions will require an analysis of the hazards and risks associated with the experiment.
The copy pages of this report must be handed in BEFORE you begin the experiment.
PRELAB REPORT (Expts 6-8)
The initial part of your lab report must be written in your laboratory notebook. A copy of the original pages
of this report will be collected prior to the experiment and will be returned to you after the whole lab is
graded. It will consist of:
a) Your name, lab section and the name of your TA (on each page).
b) The title and number of the experiment.
c) Objectives. This should include hypotheses about the outcome of the lab, which you will test by
experiment. It is your responsibility to propose what you expect to learn from each experiment.
d) Outline of procedure. This must be sufficiently detailed to allow you to perform the experiment. Make
sure you note any necessary safety precautions.
e) Chemical Table (see individual experiment for specifics). This will involve calculating the correct molar
proportions of all the chemicals you will use for the experiment. Look up molecular masses and calculate
the material amount in moles (if appropriate), boiling/melting points (bp/mp) and density (if appropriate).
f) Safety question answers. Read the MSDS forms (posted on iLearn) for the chemical used in that week’s
experiment. The questions will always require an analysis of the hazards and risks associated with the
experiment.
The copy pages of this report must be handed in BEFORE you begin the experiment.
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I. POSTLAB REPORT (60% of the report grade)
IIa. DESCRIPTION OF RESULTS (20% of the report grade)
This section should be started on a fresh page of your notebook, after the prelab report. A combined copy
of the Results/Postlab report will be stapled and turned in to your TA after the experiment is complete.
This section should be completed during the lab session and consists of:
a) Your name, lab section and the name of your TA (on each page).
b) The title and number of the experiment.
c) Describe the results from this experiment. For all experiments, make sure you write down the
measured masses and calculated yields of products, measured melting points of your products and any
other observations (color changes, etc) recorded during the lab session (if appropriate).
d) Characterization materials: include copies of spectra, etc., recorded during the lab session.
Some suggestions for points to note are given at the end of each experiment in the lab manual - this
section is descriptive, i.e. you just need to record your observations, not explain them (that part is in the
postlab analysis section).
Turn in your product(s) in a labeled vial to your TA at the end of the lab session.
IIb. ANALYSIS OF RESULTS (40% of the report grade)
This section does not need to be written in your lab notebook - it can be typed or written on separate
loose leaf sheets and stapled to your results copy pages. It is to be completed at home, after the lab
period, and consists of:
a) Your name, lab section and the name of your TA (on each page).
b) The title and number of the experiment.
c) Analysis of results:
Your goal here is to analyze what happened in the experiment, and explain why you observed what you
did. This will be broken into sections:
1) In no more than three sentences, describe the point of that week’s experiment, and your learning
outcomes.
2) Analysis Subquestions: These questions will focus on what happened in each experiment and why,
notably the quality of your results, problems that may have occurred and possible solutions.
3) Critical Analysis Questions - these will focus on why you performed the experiments you did, as well
as analyzing the material characterization (especially spectroscopic analysis) and (if necessary), the
reaction mechanism(s).
Staple Parts II and III together and turn into your TA at the beginning of the next week's lab
session.
III. LAB EXAM QUESTIONS
At the end of each experiment, there are 10 multiple choice questions based on that experiment. You
are responsible for doing the lab exam questions and understanding the answers. You will be given
the letter answers for the questions, and they are not to be handed in. Your TA will help you with the
answers if you need it.
The final lab exam will consist of 40 of the 80 questions in this manual, with the letters changed (i.e. the
chemical answer is the same, but it will be assigned a different letter than in the lab manual). If you
understand all 80 of those questions by the end of the quarter, then you will get a perfect score on the
lab exam!
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Grading Procedure
The grading procedure for this course is as follows: Your lab scores (out of 240) will be normalized to
remove any variance in TA grading (this ensures fairness, so that no-one is benefitted by a TA who
grades easily, and no-one is disadvantaged by a TA who grades more harshly). This normalized score
will be added to your lab final score (out of 240 – each question is worth 6 points). The class will be
ranked according to score, and the grades assigned based on class ranking.
As you are given all the answers to the lab report questions and the lab final exam questions, the
averages are expected to be high. The average score on the lab reports is usually ~200/240, and the
average for the exam will likely be ~220/240. The grading scale will be generous: I expect to give ~25%
A (including A-), ~45% B, if not more. But the final breakdown will be dependent on you: if the class
performs well, more high grades will be given. If you perform poorly, fewer high grades will be given. If
you hand in all your completed lab reports and perform satisfactorily on the lab exam (within one
standard deviation of the average), you will pass the class (with a C- or higher).
In addition, if you score 220 or greater on your normalized lab score, AND you score 234/240 or
greater on the lab exam, you are guaranteed an A grade. I expect to give more A grades than that,
but anyone who beats those scores will get an A, regardless of the number of students who do so.
Most importantly – this class is not graded like a high school class! As you have access to all the
answers, there is no point giving grades based on raw score. 90% does not equal an A in this class:
virtually everyone will get that score. To get an A, you must excel in the class, not just get an average
score. If you study all the lab exam questions, consult your TAs and write your lab reports clearly and
correctly, then you should have no problem getting an A grade. If you don’t, then your grade will be lower.
Check your graded lab reports carefully, and consult with your TA if you find any grading errors.
If you find an error in your lab report or lab exam grading AFTER the exam, you must schedule a
meeting to discuss this with Prof. Hooley IN PERSON. We will not respond to any emails that
request a regrade because you are unhappy with your grade.
Definitions of Common Words used in Organic Chemistry Laboratory
There are a collection of words you need to know in an organic chemistry lab, and we’ll use them
frequently in this manual. All of these terms are properly defined in Zubrick, but in case you forget:
Solution - a liquid or mixture of liquids containing no undissolved particles.
Suspension - a liquid containing some undissolved, solid particles.
Filtrate - a solution whose solids have been removed by filtration.
Filtrand - the solids removed by filtration.
Precipitate - an undissolved solid in a solution.
Separation - the process of separating two or more chemical compounds from a mixture.
Extraction vs washing - Extraction and washing are very similar: in fact, they involve the very same
physical operations. The difference is that when you extract something, you remove a product from the
mixture, leaving the impurities behind. When you wash something, you remove unwanted impurities from
a mixture, leaving the product in the original solution.
Aqueous layer - a water-based liquid (in a separatory funnel).
Organic layer - an oil-based liquid that is not miscible with water (in a separatory funnel).
Miscible - the ability of two liquids to mix without forming layers
Immiscible - not miscible.
Brine - a saturated solution of sodium chloride in water.
Elution solvent - the solvent mixture you using in thin-layer or column chromatography to move your
sample through the silica gel.
Fraction - used to describe the sequential collection of samples from column chromatography - each test
tube of solvent mixture is referred to as a fraction.
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Experiment 1 - Molecular Modeling Exercises
Reading: Solomons 12th Ed Chapter 4.
You will perform each exercise using your Darling molecular model kit. Learning how to effectively
manipulate molecular models will help you considerably in the visualization of the shapes of organic
molecules in three dimensions.
There will be no prelab report to turn in for this experiment. For a postlab report, write answers to each
question in your notebook and turn in at the end of the exercise.
Exercise No. 1:
1.1 Assemble two molecular models of methane, CH4. Draw a representation of the methane molecule
you just built using solid (
), wedged (
), and dashed (
) lines. The solid lines represent bonds
in the plane of the paper, wedged lines represents a bond coming out of the plane, and the dashed line
represents a bond going back behind the plane of the paper.
1.2 What configuration does the carbon center have?
1.3 Replace any one hydrogen atom in each of the two methane models with a halogen atom (green) to
form two molecules of CH3X.
a) Are the two structures identical?
b) Does it make a difference which of the four hydrogen atoms on a methane molecule you replace?
1.4 Replace two hydrogen atoms in each of the two methane models with two identical halogens to form
two molecules of CH2X2.
a) Are the two structures identical?
b) Does it make a difference which two of the four hydrogen atoms on a methane molecule you
replace?
1.5 Repeat 1.4 with two different halogens to form two molecules of CH2XY. Use two different colored
atoms for this.
a) Are the two structures identical?
b) Does it make a difference which two of the four hydrogen atoms on a methane molecule you
replace?
1.6 Construct two identical models of a trisubstituted methane molecule, CHXYZ, using four different
colored atoms attached to a central tetrahedral carbon atom. Compare these models.
a) Are the two structures superimposable?
b) Interchange any two substituents on one of the carbon atoms on one of the models. Are the two
CHXYZ molecules superimposable now?
c) Compare the two models that were not superimposable. What is the relationship between them?
Exercise No. 2:
2.1 Make a model of ethane, CH3CH3.
a) Does each of the carbon atoms retain a tetrahedral configuration?
b) Can the carbon atoms be rotated with respect to each other without breaking the carbon-carbon
bond?
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c) Hold the model such that you are looking at one carbon and the other carbon is directly behind it.
This is the perspective of a Newman projection. Rotate about the carbon-carbon bond until the
carbon-hydrogen bonds of one carbon atom are aligned with those of the other carbon atom. This
is called the eclipsed conformation. Draw the Newman projection of the eclipsed conformation.
d) Rotate the carbon-carbon-bond until the C-H bond of one carbon atom bisects the H-C-H angle
of the other carbon atom. This conformation is called staggered. Draw the Newman projection of
the staggered conformation.
e) In which of these two conformations of ethane are the hydrogen atoms of one carbon closest to
those of the other carbon?
2.2 Replace any one hydrogen on the ethane model with a substituent such as a halogen to form a
model of CH3CH2X.
a) How many staggered conformations are possible?
b) How many eclipsed conformations are possible?
2.3 Prepare a second model of CH3CH2X.
a) Are the structures identical?
b) If not, can they be made identical by rotation about the C-C bond?
2.4 Assemble a model of a 1,2-disubstituted ethane molecule, CH2XCH2X. Note how the orientation and
the distance between the X groups changes with rotation of the carbon-carbon bond.
a) How many eclipsed conformations are possible?
b) Draw the Newman projection of the eclipsed conformation where the two halogen atoms are
closest to each other.
c) The arrangement in which the X substituents are at maximum separation is called the anti
conformation. How many anti conformations are possible?
d) The other staggered conformations are called gauche conformations. How many gauche
conformations are possible?
e) Are all gauche conformations identical?
Exercise No. 3:
Build a model of 2-butene, CH3CHCHCH3.
a) How many different structures are there? Draw the structures.
b) Are those structures identical?
c) Compare the two structures that are not identical, is it possible to rotate the bond between C2-C3
to make them identical?
Exercise No. 4:
4.1 Build a model of cyclopentane, C5H10. Cyclopentane is a more flexible ring system than cyclobutane
or cyclopropane. A model of cyclopentane in a conformation with all the ring carbon atoms coplanar
exhibits minimal deviation of the C-C-C bond angles from the normal tetrahedral bond angle.
a) How many eclipsing interactions are there in this planar conformation?
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b) If one of the ring carbon atoms is pushed slightly above (or below) the plane of the other carbon
atoms a model of the envelope conformation is obtained. Does the envelope conformation
relieve some of the eclipsing interactions?
Exercise No. 5:
5.1 Assemble the six-membered ring compound cyclohexane, C6H12. Rotate about the carbon-carbon
bonds of the ring to show a chair conformation. In the chair conformation carbon atoms 2, 3, 5, and 6 are
in the same plane and carbon atoms 1 and 4 are above and below the plane, respectively.
a) Draw a chair conformation in Newman projection.
b) Are the hydrogen atoms in the chair conformation staggered or eclipsed?
c) How many eclipsing interactions are there?
d) Do carbon atoms 1 and 4 have an anti or a gauche relationship? (Hint: Look down the C-2, C3 bond).
5.2 From the chair conformation, rotate about the carbon-carbon bonds of the ring to form a boat
conformation. In the boat conformation carbon atoms 1 and 4 are both above (they could also both be
below) the plane described by carbon atoms 2, 3, 5 and 6.
a) Are the hydrogen atoms in the boat conformation staggered or eclipsed?
b) How many eclipsing interactions are there?
c) Do carbon atoms 1 and 4 have an anti or a gauche relationship?
5.3 A twist-boat conformation of cyclohexane may be obtained by slightly twisting carbon atoms 2 and 5
of the boat conformation. Note that the C-2, C-3 and the C-5, C-6 bonds no longer retain their parallel
orientation in the twist conformation. If the ring system is twisted too far, another boat conformation
results.
a) Compare the number of eclipsing interactions present in the boat, twist and chair conformations
of cyclohexane. Predict the relative order of thermodynamic stabilities between chair, twist, and
boat conformation.
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Final Exam Questions, Experiment 1.
NOTE - these questions cover material you will go over in the first 3 weeks of class. They will be
on the final, but you haven’t covered the material yet. Come back to these questions after you
cover Chapter 4 of Solomons in class (or read ahead).
1) Only one of these molecules is drawn correctly, with the correct structure and bond angles. Which?
2) One "stick" representation is correct. Which?
3) Which of the following alkane conformations has the lowest energy?
4) Only one of the molecules below is correctly named. Which one?
5) The molecule below has been redrawn from different viewpoints. Three show the same molecule from
a different viewing angle, one is a different molecule. Which one is the wrong molecule?
6) Which chair form is the correct representation for this molecule?
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7) Which of the molecules below is in the lowest energy conformation?
8) In each example, the most stable cyclohexane conformation is circled. One is wrong. Which?
9) How many stereoisomers are possible for the molecule below?
10) How many constitutional isomers are possible for the molecule below? Ignore stereoisomers.
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Experiment 2 - Techniques Lab 1: Extraction of Solids
Reading: The Organic Chem Lab Survival Manual: pp. 74-91, 114-127, 179-182.
Introduction
In this experiment, you will be separating a mixture of three different chemicals: acetaminophen, aspirin,
and caffeine. You will also be purifying each individual chemical. These chemicals can be found together
in many over-the-counter headache medicines. To perform this experiment, you will also learn the
techniques of solution-phase extraction and how to use a rotary evaporator.
Figure 1. Structures of acetaminophen, aspirin, and caffeine.
The three components of the mixture have different properties - caffeine is an organic base, aspirin is an
acid, and acetaminophen is a neutral compound. You will use these properties to separate the
components from each other.
Prelab
In this experiment, we will use a “flipped lab” concept. Your prelab exercises will mainly consist of viewing
a video (posted on iLearn) that shows you a generic procedure for separations, gravity filtration and the
use of the rotary evaporator.
1) Watch the Week 2 video posted on iLearn (entitled “Separations and Rotovap”). We will track
the views of the video - there will be pre-lab quiz questions on it!
2) Read the relevant passages of The Organic Chem Lab Survival Manual and the summary passages
below.
Technique Summaries
A. Extraction
“Extraction and Washing” - The Organic Chem Lab Survival Manual, pp. 114-127. Pay particular to the
section entitled “How to Extract and Wash What”, pp. 119-127.
Solution-phase extractions are one of the more complicated parts of organic lab, and it is very important
to understand which compounds are extracted into which phases. It is also important to keep track of
which phase is the organic phase and which is the aqueous phase.
Some relevant points to remember:
• The two layers must be immiscible with each other (e.g. acetone is a poor extraction solvent, as it is
miscible with water - you will use dichloromethane most often). Depending on its density, the organic
phase may be the top or the bottom layer. NOTE - dichloromethane is HEAVIER THAN WATER!
• Extracting a layer more than once will yield better results.
• Strong organic acids may be extracted with saturated NaHCO3 solution.
• Weak organic acids may be extracted with 10% NaOH solution.
• Organic bases may be extracted with 10% HCl solution.
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• Adding 2-3 drops of the top layer to a small test tube half-full of water can help you determine if the top
layer is the aqueous layer. If drops dissolve into the water, the layer is the aqueous layer. If not, then it is
the organic layer.
• Save both layers until you know it is safe to throw away the unwanted layer.
B. The Rotary Evaporator (“Rotovap”)
“The Rotary Evaporator” - The Organic Chem Lab Survival Manual, pp. 179-182.
The rotovap is used to evaporate solvent from a sample under reduced pressure – it is typically a more
efficient method than a steam bath or a still. In order to maintain the equipment, the following steps should
be taken:
• Make sure the condenser has dry ice/acetone in it to allow for collection of the solvent.
• Only half-fill your flask with the organic solution to avoid “bumping". Also, ensure that only one phase
is present in the flask and do not set the water bath temperature too high, as this may also lead to
bumping.
Prelab Quiz
Your TA will give you a pre-lab quiz on the topics in the video and in the relevant Zubrick reading before
your lab starts. This will be worth 4 points of your lab score.
Prelab Report
Objectives (2 pts): Describe the central objective of this experiment. Describe one learning outcome
you expect to have gained at the end of this experiment.
Procedure and Chemical List (3 pts):
In your prelab report, write an outline of the experimental procedure and a table including the name,
formula and boiling point of all liquids and solutions to be used in this experiment. Remember to
include your name, lab section and the name of your TA (on each page), and the title and number of the
experiment.
Safety and Preparedness (3 pts)
The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read
these and answer the following questions:
1) What is the greatest hazard posed by using aqueous hydrochloric acid?
2) If you spill sodium hydroxide solution on your skin, what should you do?
3) What is the greatest hazard posed by using dichloromethane?
Experiment
1. Preliminary Separation
Obtain a sample (approximately 1.0 g) of the mixture. Weigh the sample, and record the weight. This
sample should consist of a 2:1:1 mixture (by mass) of aspirin, acetaminophen and caffeine, respectively.
Assemble the apparatus for a vacuum filtration (Zubrick p98), making sure the receiving flask is clean;
you will be keeping both the filtrate and the insoluble material.
Transfer the sample to your smallest Erlenmeyer flask, add 10 mL of dichloromethane, and warm the
mixture for ten minutes on a hot plate at 35-40 °C. Note that a portion of the sample will not dissolve. Wet
the filter paper in the Büchner funnel with dichloromethane, and filter the mixture.
The filtration must be performed while the mixture is still warm – the success of your separation
depends on this. Ensure that you have good suction in your filtration apparatus, and pour the
solution quickly and smoothly to avoid crystallization in the filter.
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Rinse the Erlenmeyer flask out with an additional 2 mL of warm dichloromethane to transfer as much
solid material to the Büchner funnel. Add an additional 5 mL of dichloromethane to the filtrate to redissolve
any crystals that might have formed during the filtration. Label the filtrate Solution A. Allow the insoluble
material to dry until you have completed steps 2 and 3.
2. Separation of Aspirin
Solution A should contain the aspirin (an organic acid) and caffeine (an organic base). Aspirin may be
separated from caffeine by extraction with 10% NaOH solution. Transfer Solution A to a 125 mL
separatory funnel and add 10 mL of 10% NaOH solution. Shake the mixture 3 or 4 times and remember
to vent the separatory funnel intermittently to relieve pressure (make sure you point the funnel away from
both yourself and your labmates!). Remove the bottom layer into a clean 25 mL Erlenmeyer flask, and
transfer the top layer to a separate clean 50 mL Erlenmeyer flask. Label the flask containing the top layer
Solution B. Pour the bottom layer back into the separatory funnel (remember to close the stopcock), add
5 mL of distilled water, and shake again.
Remove the bottom (organic) layer into a clean, dry 25 mL Erlenmeyer flask, and add anhydrous sodium
sulfate until the drying agent no longer clumps together. Label this mixture Solution C. The remaining
aqueous layer (the top layer still in the separatory funnel) should be added to Solution B.
3. Recrystallization of Aspirin
Solution B contains the aspirin in the form of a water-soluble sodium salt. Slowly add 4M hydrochloric
acid solution to Solution B until it becomes strongly acidic and an obvious persistent precipitate forms.
Test the acidity using pH paper. The aspirin should rapidly precipitate (“crash”) from solution. On a hot
plate, heat the solution until all the aspirin has re-dissolved, then allow the solution to slowly cool to room
temperature and place it in an ice bath. Isolate the formed crystals by vacuum filtration.
4. Isolation of Caffeine
Solution C contains neutral caffeine. Decant the solution from the drying agent using a transfer pipette,
and transfer the material to a clean, pre-weighed, 50 mL round-bottomed flask. Remove the
dichloromethane using the rotovap to yield the caffeine.
Weigh each of the isolated materials (aspirin, acetaminophen and caffeine), and record their masses in
your laboratory notebook. Determine the melting point range of your caffeine sample, using a Mel-Temp
apparatus.
Post Lab Report
Description of Results (6 points): Describe the observations from this experiment - see p6 for more
details. Specific points to note: What were the masses that you recovered for each component of the
mixture before any purification? How much aspirin (by mass) did you recover after recrystallization? What
was your recorded melting point of caffeine?
Analysis of Results (12 points):
1) (3 points) In no more than three sentences, describe the point of this experiment and what you
learned - why did you perform an aqueous extraction, and how was it successful?
2) Analysis subquestions (5 points): Describe how effectively you separated the three components. What
was your recovered yield of each of the three components? Was the sample truly a 2:1:1 mixture (by
mass) of aspirin, acetaminophen and caffeine? Describe why and how the procedure effected separation
of aspirin, acetaminophen and caffeine.
3) Critical analysis (4 points):
(a) Compare your melting point data to the literature values. How can this tell you the purity of the
materials you isolated?
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(b) Using the arrow formalism, draw the mechanism of the reaction of aspirin with aqueous sodium
hydroxide to form the corresponding salt.
(c) What is the difference between a rapid precipitation and a recrystallization?
Final Exam Questions, Experiment 2
1) Which of these compounds would be extracted from an organic solution by aqueous acid?
2) When doing the aspirin/caffeine/acetaminophen extraction, the dichloromethane solution is washed
with water. Which of the following is true?
a) water is the bottom layer because it is less dense than dichloromethane.
b) water is the bottom layer because it is more dense than dichloromethane.
c) dichloromethane is the bottom layer because it is less dense than water.
d) dichloromethane is the bottom layer because it is more dense than water.
3) Which of these compounds would be extracted from an organic solution by aqueous base?
4) Which molecule is the MOST acidic?
5) Which molecule is the MOST basic?
6) What safety hazards should be considered when using 4M hydrochloric acid?
a) It is a low boiling solvent with a high vapor pressure.
b) It is highly flammable.
c) It is a corrosive solution.
d) It is a List II Regulated chemical.
e) All of the above.
7) Which of these hazards must be considered when using dichloromethane?
a) It is a low boiling solvent with a high vapor pressure.
b) It is highly flammable.
c) It passes quickly through latex gloves.
d) It is a known carcinogen.
e) All of the above.
8) After the liquid-liquid extraction of caffeine, you are removing the dichloromethane solvent on the rotary
evaporator. After 30 mins the solvent volume has not decreased. This may be because:
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a) You have the aqueous layer on the rotary evaporator and are trying to remove water, instead
of the organic layer.
b) It typically takes 30 mins to remove the low-boiling dichloromethane solvent on a rotary
evaporator.
c) You picked up the wrong solvent bottle, and this isn’t dichloromethane.
d) You forgot to close the vent on the rotary evaporator.
e) Either a), c) or d).
9) You’re performing an aqueous extraction, and you forget which layer is the organic layer and which is
the aqueous layer. What is the best way to solve this problem?
a) Add a small amount of sodium sulfate - if it dissolves, the layer is water.
b) Remove all the solvents via rotary evaporation and start again.
c) Smell the two layers to see which one is an organic solvent.
d) Pick the top layer, as that is always the organic layer.
10) How much sodium sulfate should you add to dry your organic layer after an aqueous extraction?
a) Three spatulas worth.
b) More. Always add more.
c) Enough solid so that when you swirl the flask, the solid isn’t all clumped at the bottom, and
swirls with the liquid.
d) 400 grams.
e) All of it.
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Experiment 3: Techniques Lab 2 - Purification by Chromatography and Recrystallization
Reading: The Organic Chem Lab Survival Manual: pp. 74-91, 92-107, 202-213, 214-221
Introduction
In this experiment, you will attempt to purify a neutral organic compound that is not amenable to
purification by a simple extraction procedure. The target compound, biphenyl, will be purified by column
chromatography and recrystallization, and you will determine its solubility in various organic solvents prior
to purification.
Figure 1. Structures of biphenyl and Methyl Orange.
Prelab
In this experiment, we will use a “flipped lab” concept. Your prelab exercises will mainly consist of viewing
a video (posted on iLearn) that shows you a generic procedure for performing recrystallization and thin
layer chromatography.
1) Watch the Week 3 video posted on iLearn (entitled “Recrystallization and TLC”). We will track
the views of the video - there will be pre-lab quiz questions on it!
2) Read the relevant passages of The Organic Chem Lab Survival Manual and the summaries below.
Technique Summaries
A. Recrystallization
"General Recrystallization Procedure” - The Organic Chem Lab Survival Manual, pp. 92-107.
Begin by placing your crude solid in a round-bottomed flask, Erlenmeyer flask or beaker. Secure this
flask in a heating apparatus (sand bath, water bath, etc) slightly below the boiling temperature of your
solvent. In a separate beaker, warm your recrystallization solvent to just below boiling. Using a Pasteur
pipette, add the solvent dropwise while agitating the test tube until there is just enough solvent to
completely dissolve the sample. Having a minimal amount of solvent is crucial. Remove the test tube
from the water bath and allow to cool to room temperature. If no crystals form, place the test tube on ice.
If crystals still do not form, scratch the inside of the test tube with a metal spatula to seed crystal growth.
B. Thin-Layer Chromatography (TLC)
“Thin-Layer Chromatography” - The Organic Chem Lab Survival Manual, pp. 202-213.
Thin Layer Chromatography is a method for the identification of organic compounds, and the
determination the purity of that compound. To get the best results:
• Make sure to mark both the origin line and the solvent front on the TLC plate in pencil.
• Avoid getting fingerprints on the TLC plate - hold the plate by the sides when handling.
• When spotting TLC plates, try to make the smallest spot possible. This will ensure that different spots
don’t run together.
• When placing TLC Plate in the development chamber ensure that the solvent level lies below the origin
line.
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Prelab Quiz
Your TA will give you a pre-lab quiz on the topics in the video and in the relevant Zubrick reading before
your lab starts. This will be worth 4 points of your lab score.
Prelab Report
Objectives (2 pts): Describe the central objective of this experiment. Describe one learning outcome
you expect to have gained at the end of this experiment.
Procedure and Chemical List (3 pts):
In your prelab report, write an outline of the experimental procedure and a table including the name,
formula, density and boiling point of all solvents to be used in this experiment. Also include the name
and formula of all solid chemicals. Remember to include your name, lab section and the name of your
TA (on each page), and the title and number of the experiment.
Safety and Preparedness (3 pts)
The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read
these and answer the following questions:
1) What is the greatest hazard posed by using methanol?
2) If you breathe acetone vapor, what should you do?
3) What is the greatest hazard posed by using hexanes?
Experimental
1. Determination of a Suitable Recrystallization Solvent
You will require five medium sized test tubes (1.3 x 10 cm). Measure out 1 mL of each of the following
solvents and add the solvent to each of the five test tubes: methanol, acetone, dichloromethane, toluene,
and hexanes. [Note: each test tube will contain a different solvent].
Determine the solubility of pure biphenyl in the solvents specified in your lab report book and record your
observations for solubilities in both cold and hot solvent. The aim is to find a solvent that will not dissolve
biphenyl at room temperature, but will dissolve when hot.
2. Purification by Recrystallization
Next, weigh and transfer approximately 0.5 g of your crude sample to an Erlenmeyer flask. Record the
amount of crude material used. Over a sand bath, slowly add hot hexanes to your sample until no more
solid dissolves. Remove the dye by vacuum filtration (using a vacuum trap) into a pre-weighed 50 mL
side arm flask. The solvent in the sidearm flask should evaporate under the vacuum. Record the weight
of crude biphenyl in the filter flask.
To recrystallize the biphenyl, prepare a hot saturated solution by adding a minimum amount of hot
methanol dropwise until all the solid has dissolved. When all the solid has dissolved, remove the solution
from the heat source, allowing the hot saturated solution to cool to room temperature. Then place the
flask into an ice bath and let the crystals form. Collect the crystals by vacuum filtration then using icecold methanol rinse the flask and wash the crystals. Record the weight of the dried crystals. You will be
required to use your product, as well as the remaining crude, for the next experiment.
3. Analysis by TLC
Set up two clean, dry test tubes and label them as ‘Crude’ and ‘Recrystallized' Biphenyl. Transfer a small
amount (e.g. the tip of a spatula) of your recrystallized sample to the appropriately labeled test tube. Add
1 mL of acetone and shake to dissolve. (Caution: take care not to let the contents of the test tube come
into contact with the test tube stopper). Place a small amount of crude compound into the second labeled
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test tube and add 1 mL of acetone to dissolve. On a silica TLC plate, draw a baseline and mark 2 positions
for the ‘Crude’ and ‘Recrystallized' Biphenyl. Using a micropipette, spot each of the solutions above onto
the corresponding position on the TLC plate. Use hexane:ethyl acetate (4:1) as the eluent to develop the
TLC plate and then visualize under a UV lamp. Make sure you mark the position the solvent travelled
to in pencil before it evaporates!
4. Purification by Silica Gel Chromatography and TLC Analysis
Take a long Pasteur pipette and lightly push a small ball of cotton into the base of the pipette. This will
serve as your pipette column. Take your pipette to the fume hood and add silica to about half way up the
pipette column. Carefully, clamp the pipette at your bench. In a 10 mL graduated cylinder, make up a 4:1
solution of hexane:ethyl acetate and then transfer the solution (eluent) to an Erlenmeyer flask. Using a
fresh pipette, transfer some of this eluent to your micropipette and allow the eluent to slowly pass through
the column using the pipette bulb. Place a clean test tube under the tip of the column to collect the eluent
that passes through. Once the eluent has eluted through the column, add 50 mg of your crude sample
(dissolved in a minimum amount of acetone) to the surface of the silica. (Due to acetone’s polarity, adding
too much can damage the column). Pass eluent through the column and collect approximately 1 mL of
the eluent in small numbered test tubes. (This is also known as ‘collecting fractions’). Collect fractions
until a colored band can be observed in the middle of the pipette column (collect at least 3 fractions).
On a TLC plate, spot all of these fractions to determine if you have collected biphenyl and in which
fractions it is contained. Develop the TLC plate and visualize with a UV lamp.
Calculate the Rf value of both biphenyl and methyl orange on your TLC plate (Zubrick p207) of your
spots. This is defined as:
Rf = distance travelled by your spot in cm/distance travelled by the solvent in cm
Combine the fractions that contain pure biphenyl into a dry, weighed, 50 mL round-bottomed flask. Make
sure to record the mass of your flask! Remove the solvent on the rotary evaporator, then determine the
mass of biphenyl by obtaining the weight of the flask plus the biphenyl sample.
5. Melting Point Determination: Read Zubrick, pp. 74-91
Follow the procedure for acquiring melting points and determine the melting points for:
a) The original sample (crude)
b) The recrystallized biphenyl
Post Lab Report
Description of Results (6 points): Describe the observations from this experiment - see p6 for more
details. Specific points to note: What was the best recrystallization solvent? What was the mass of your
recrystallized biphenyl? Draw the results of the TLC experiment - draw an image of your plate, showing
where each spot was after elution. Which fractions from your column contained biphenyl? How much did
you recover? What were the melting points of crude and recrystallized biphenyl?
Analysis of Results (12 points):
1) (3 points) In no more than three sentences, describe the point of this experiment - why did you
perform purification via recrystallization and column chromatography, and what is thin layer
chromatography used for?
2) Analysis subquestions (6 points):
(a) Compare your TLC analysis with the results of the column chromatography. More polar molecules
move more slowly through silica than less polar molecules. Describe why silica gel chromatography is
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a good method of separating methyl orange from biphenyl. Based on the structure of Biphenyl and Methyl
Orange, predict which compound will have a higher Rf value on TLC and explain your choice.
(b) More polar solvents (eluents) move molecules more rapidly than less polar solvents. If you used a 1:1
hexanes:methanol mixture as solvent, would you expect the products to elute faster or slower? Based on
your experiment, would a 1:1 hexanes:methanol mixture be a good choice as eluent? Explain why/why
not.
3) Critical analysis (3 points):
(a) Impure compounds tend to have lower melting points than pure samples. Explain why this occurs,
using biphenyl as an example. Make sure you consider what happens upon melting in molecular terms.
(b) Is recrystallization a suitable method for purifying all types of organic compounds? If not, why not?
Final Exam Questions, Experiment 3
1) In thin-layer chromatography on silica gel TLC plates, which of these is true?
a) More polar compounds move faster because they have lesser affinity for the polar silica.
b) More polar compounds move slower because they have lesser affinity for the polar silica.
c) More polar compounds move slower because they have greater affinity for the polar silica.
d) Less polar compounds move slower because they have lesser affinity for the polar silica.
2) Silica gel column chromatography of biphenyl used 4:1 hexane:ethyl acetate as the solvent. If it were
changed to 1:4 hexane:ethyl acetate, how would this affect the elution of biphenyl?
a) no change
b) it would elute sooner
c) it would elute later
3) A TLC analysis is performed on both crude and purified biphenyl. Upon visualization under the UVlamp both spots remain at the baseline. This is likely because:
a) The samples were not spotted properly on the TLC plate.
b) Biphenyl is a polar molecule and therefore should remain at the baseline upon TLC plate
development in the proper eluent.
c) The solvent was too polar.
d) The solvent was too non-polar.
e) The solvent evaporated before the TLC plate could be added to the chamber.
4) Give the Rf of the spot in this TLC.
5) When choosing a recrystallization solvent, what properties must be considered?
a) Its boiling point.
b) The solubility of the compound to be crystallized.
c) Both A and B.
d) Neither A nor B.
6) Why does scratching the side of the flask with a spatula help form crystals?
a) The spatula is made of iron, which helps crystallization.
b) The scratch provides a nucleation site for crystal growth to start.
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c) The spatula cools the solution, aiding recrystallization.
d) Crystals can form on the spatula surface.
7) Why should you wash your crystals in ice cold solvent after recrystallization?
a) Ice is polar, so will not dissolve your crystals.
b) Cold solvent is better at dissolving molecules.
c) Room temperature solvent will dissolve your crystals, lowering your yield.
d) Ice helps the recrystallization.
8) If you use toluene as a solvent for recrystallization of biphenyl, what is the most likely reason it would
be unsuccessful?
a) Toluene is a polar solvent.
b) Biphenyl is too soluble in the similarly structured toluene solvent, and will be hard to recover
after recrystallization.
c) Biphenyl will not dissolve in the non-polar toluene.
d) The boiling point of toluene is too low.
9) You perform a recrystallization of biphenyl, but when you cool the solution, no crystals form. What is
the most likely explanation?
a) The solution was cooled too slowly.
b) The solution was cooled too quickly.
c) Too much hot solvent was added to dissolve the solid.
d) Too little hot solvent was added to dissolve the solid.
10) When you run a TLC plate with methyl orange and biphenyl, you observe very large, broad, streaky
spots on the plate under the UV light. What is the most likely explanation?
a) The elution solvent was not polar enough.
b) Too little sample was spotted onto the TLC plate.
c) Too much sample was spotted onto the TLC plate.
d) The elution solvent was too polar.
e) The Rf of the components was too high.
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Experiment 4: Purification of Liquids – Distillation
Reading: The Organic Chem Lab Survival Manual, pp. 150-174, 245-271.
Introduction
Organic liquids are often purified by distillation. In this experiment, you will investigate the factors that
affect the efficiency of a distillation, by attempting to separate a mixture of two miscible liquids using
simple distillation techniques.
Safety Notes
• The use of bunsen burners in this experiment is strictly prohibited. Heating mantles or sand baths are
to be used. Carefully inspect your glassware for star cracks.
• You require either a stirrer or boiling chips in your flask to allow controlled boiling of the liquid. If your
distillation “bumps”, you will have to start again.
Prelab
In this experiment, we will use a “flipped lab” concept. Your prelab exercises will mainly consist of viewing
a video (posted on iLearn) that shows you a generic procedure for distillation.
1) Watch the Week 4 video posted on iLearn (entitled “Distillation”). We will track the views of the
video - there will be pre-lab quiz questions on it!
2) Read the relevant passages of The Organic Chem Lab Survival Manual and the summary passages
below.
Technique Summaries
Distillation
1. “Simple Distillation” - The Organic Chem
Lab Survival Manual, pp. 151-156.
Simple Distillation is a useful technique for
separating miscible liquids with boiling points
below 150 °C, and differ by at least 25 °C.
Below are things to remember when doing
any simple distillation.
• Make sure that there is some solid surface
present in the liquid that allows bubbles to
nucleate on its surface, and ensures smooth
boiling. Rough or intermittent boiling due to
superheated
solvent
spontaneously
vaporizing (bumping) leads to poor
separation, and can be dangerous. A boiling
chip is added to the distilling flask, but never
to a hot liquid.
• Make sure that water is running through the
condenser to ensure collection of the
distillate.
Figure 1. Schematic of a simple distillation apparatus
• Make sure that you clamp down all pieces of
glassware securely and all joints are properly
secured using Keck clips or rubber bands.
• DO NOT heat too quickly, as this will lead to a poor separation.
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2. “Infra-red Spectroscopy” - The Organic Chem Lab Survival Manual, pp. 245-271, Solomons 12th Ed
pp 86-97.
IR spectroscopy provides a way of identifying organic compounds on the basis of the functional groups
present in that compound – many functional groups have characteristic regions in the infra-red spectrum
where they absorb. It is possible to identify these functional groups (and in some cases, as in this one)
to determine structural information from infra-red spectra. You will take IR spectra of your two products
from this distillation and analyze the differences.
Prelab Quiz
Your TA will give you a pre-lab quiz on the topics in the video and in the relevant Zubrick reading before
your lab starts. This will be worth 4 points of your lab score.
Prelab Report
Objectives (2 pts): Describe the central objective of this experiment. Describe one learning outcome
you expect to have gained at the end of this experiment.
Procedure and Chemical Table (3 pts):
In your prelab report, write an outline of the experimental procedure. Remember to include your name,
lab section and the name of your TA (on each page), and the title and number of the experiment.
Fill in the table below. Make sure you correctly calculate the molar amounts of your two materials.
name
formula
MW
bp/ºC
moles
density
amount
Methyl tert-butyl
ether (MTBE)
12 mL
Butan-1-ol
12 mL
Safety and Preparedness (3pts):
The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read
these and answer the following questions:
1) What is the greatest hazard posed by using MTBE?
2) If you swallow butanol, what should you do?
3) What is the greatest hazard posed by distilling flammable solvents?
Experiment
Collect 12 mL of methyl tert-butyl ether and 12 mL of n-butanol, and combine them in a 50 mL round
bottom flask.
Add a single boiling chip to the flask, and set up the distillation still (see Figure 1). The stills must be
clamped as shown in Figure 1 for structural stability. Note that certain clamps should only supply support
and should not be clamped too tightly. Tight clamping may place strain on the glass, causing it to break.
Condensers and take-off adapters should be held in place with rubber bands or Keck clips.
Heat the flask to 80 ºC and collect the distillate. DO NOT HEAT TOO VIGOROUSLY AT THE START.
Once the solution stops boiling, heat to 140 ºC until boiling occurs, then collect fraction #2. Do not allow
the flask to boil dry.
Determine the boiling point range for the two fractions by reading the thermometer attached to the
stillhead as the fractions are distilling. For each fraction, note the boiling point in your lab notebook.
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NOTE - Ensure your flask is properly heated so that distillation proceeds smoothly. Make sure
the level of the sand in the sand bath is at the level of the solvent in the flask. If the product is not
distilling, wrap the condenser and stillhead in aluminum foil.
Characterization
Obtain the infra-red spectrum of a thin film of the material – your instructor will show you how to do this.
Make sure that you have identified the frequencies of the major absorbance peaks on your infra-red
spectrum.
• The infra-red spectrum is usually collected in transmission mode – therefore absorbance is indicated
by troughs in the spectrum (% transmission < 100%), rather than peaks.
• The frequency of light in the infra-red spectrum is typically expressed in terms of wavenumbers (cm-1),
rather than the usual hertz (s-1). Wavenumbers are in fact reciprocal wavelength (1/λ) where λ is
expressed in cm, rather than m. It can be shown from the wave equation for light that reciprocal
wavelength is in fact proportional to frequency.
Take IR spectra of your two fractions (which should have different boiling points). Print out the spectra
and hand them in with your report.
Post Lab Report
Description of Results (6 points): Describe the observations from this experiment - see p6 for more
details. Specific points to note: What were the observed boiling points of your two molecules? Note the
important peaks that can identify each molecule on the IR spectra. Did you get good separation in your
distillation? What was the recovered volume in each fraction?
Analysis of Results (12 points):
1) (3 points) In no more than three sentences, describe the point of this experiment - why did you
perform a distillation to separate these two molecules, and how/why was it successful?
2) Analysis subquestions (4 points):
(a) Draw the structure of methyl tert-butyl ether and n-butanol and identify the functional groups in each.
(b) There is one glaring difference (i.e. an obvious extra peak in one of the spectra) in the IR spectra of
methyl tert-butyl ether and n-butanol. What is it? What functional group does this peak denote?
(c) Which molecule has a higher boiling point, methyl tert-butyl ether or n-butanol? Explain why.
3) Critical analysis (5 points):
(a) Boiling point is directly related to the strength of the intermolecular forces between each molecule.
Describe three different intermolecular forces that are present in a liquid sample of n-butanol. Which of
these intermolecular forces is strongest?
(b) Van der Waals forces are determined by the size of the molecule. Which of the two molecules is
larger? Are Van der Waals forces an important contributor to the relative boiling points of these two
samples? Why/why not?
Final Exam Questions, Experiment 4
1) Which molecule has the highest boiling point?
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2) Which molecule has the highest boiling point?
3) Here is an IR spectrum of one of the molecules below. Which one?
4) Here is an IR spectrum of one of the molecules below. Which one?
5) Here is a complex molecule, with multiple functional groups. Only one of the entries describing the
functional groups is correct - which one?
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6) Here is a complex molecule, which will have multiple intermolecular forces in the liquid state. Only one
of the entries describing the intermolecular forces is correct - which one?
7) Which of the distillation setups below is correct?
8) You distill a mixture of methyl tert-butyl ether and butanol, and get two fractions. You have forgotten
the boiling points of the two species, and can’t work out which is which. What do you do?
a) Take IR spectra of each sample - the one with a peak around 3400 cm-1 is butanol.
b) Ask your TA.
c) Take IR spectra of each sample - the one with a peak around 2950 cm-1 is butanol.
d) Smell the two liquids - butanol is the one that smells like tequila.
e) Combine the two fractions into one, and distill them again.
9) You are performing a distillation. The sand bath is heated to temperature, the sample is boiling, but no
distillate is being collected. What should you do?
a) Turn up the heat on the hotplate.
b) Take a heat gun and warm the flask further.
c) Make sure the condenser and stillhead are properly insulated by wrapping them in cotton wool
and aluminum foil.
d) Add a boiling chip to the flask.
e) None of the above.
10) You are trying to purify toluene, which is contaminated by some water, by performing a distillation.
When your first fractions come out and cool, they separate into two layers. What happened?
a) The boiling points of water and toluene are too similar to allow separation by distillation.
b) Water and toluene mix, so cannot be separated via distillation.
c) The toluene and water formed an azeotrope and distilled at the same temperature.
d) The distillation temperature was too low.
e) None of the above.
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Experiment 5: Natural Products - Isolation and Characterization of Limonene from Orange
Peel
Reading: The Organic Chem Lab Survival Manual, pp. 168-172, 245-271.
Bring a fresh orange peel to the lab with you for this experiment.
Introduction
In this experiment, we will extract a natural product from plant material (in this case orange peel), then
purify and characterize it. This type of experiment forms the historical foundation to organic chemistry,
and is still used today to obtain interesting chemicals (e.g. pharmaceuticals) from biological materials.
1. Steam Distillation
“Steam Distillation” - The Organic Chem Lab Survival Manual, pp. 168-172.
Steam Distillation is used to isolate tars, oils, and natural products that are either slightly soluble or
insoluble in water. Below are a few pointers to remember when doing a steam distillation.
• Be careful when handling any piece of glassware as it will be extremely hot.
• In this lab, you will not be doing a steam distillation as described in Zubrick, but a variation which involves
a simple distillation of a water/orange peel mixture.
2. Specific Optical Rotation
The natural product obtained from distillation of orange peel is limonene, which is a chiral molecule. To
determine the optical purity of your product, you will analyze it by determining its specific optical rotation,
a method used to identify and gauge the purity of chiral compounds. There is no section in Zubrick
regarding the measurement of specific optical rotation, so we will describe it briefly here. You may recall
from lecture (and Solomons, p196-198) that two enantiomers of a chiral compound share identical
physical properties – the only way they differ is in their reaction with plane-polarized light. An enantiomer
allowed to interact with plane polarized light is capable of rotating the plane of that polarization – an
optical rotation that may be to the left or right. The opposite enantiomer will exhibit the same magnitude
of rotation, but in the opposite direction. The angle of rotation may be measured using a polarimeter, for
which a simplified schematic is shown in Figure 1.
Figure 1. Simplified schematic of a polarimeter
The magnitude of the optical rotation depends on a number of factors: the temperature, the wavelength
of the incoming light, the length of the cell l (in dm), and the concentration c (in g/mL or mol/L; and optical
or enantiomeric purity) of the sample, among others. Thus, we need a standard formalism for optical
rotation, which is the specific optical rotation, [α25D], measured at 25 °C, using the wavelength of the
sodium “D-line” at 589 nm. The specific optical rotation is determined from the observed optical rotation
α25D by:
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Prelab Quiz
Your TA will give you a pre-lab quiz on the relevant Zubrick reading before your lab starts. This will be
worth 4 points of your lab score.
Prelab Report
Objectives (2 pts): Describe the central objective of this experiment. Describe one learning outcome
you expect to have gained at the end of this experiment.
Procedure and Chemical List (3 pts):
In your prelab report, write an outline of the experimental procedure, and a table including the name,
formula, density and boiling point of all solvents to be used in this experiment. Remember to include
your name, lab section and the name of your TA (on each page), and the title and number of the
experiment.
Safety and Preparedness (3pts):
The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read
these and answer the following questions:
1) What is the greatest hazard posed by using a steam distillation apparatus?
2) If you spill diethyl ether in your eyes, what should you do?
3) What is the greatest hazard posed by using steam?
Experiment
1. Isolation of Orange Oil
Cut the peel of a large orange into 1cm x 1cm portions.
You can remove the white pulp, it does not contain much
limonene. Add the pieces to a 250 mL round bottomed
distilling flask (obtained from your TA). Add 150 mL
distilled water. Do not grind the orange peel too finely,
otherwise the subsequent distillation step will be made
very difficult because of foaming in the sample.
Steam distill this mixture, collecting at least 30 mL of
distillate in a 100 mL Erlenmeyer flask. Transfer the
distillate to a 125 mL separatory funnel and extract the
mixture three times with 10 mL portions of diethyl ether.
Note that ether is less dense than water - the organic
layer in this experiment is the top layer.
NOTE - Ensure your flask is properly heated so that
distillation proceeds smoothly. Make sure the level of
the sand in the sand bath is at the level of the solvent
in the flask. If the product is not distilling, wrap the
condenser and stillhead in aluminum foil.
Figure 1. Schematic of a simple steam
distillation apparatus
Combine the three extracts in a flask, and dry them over anhydrous sodium sulfate. Filter the combined,
dried extracts through a plug of cotton wool into a weighed 50 mL round-bottomed flask. Wash the
remaining sodium sulfate residue in the funnel and drying flask with another 5 mL of ether. Remove the
solvent on the rotary evaporator. About 0.5 mL of material will remain, as 30 mL of steam distillate usually
produces approximately half a gram of material – this is not an exact amount, there is a lot of variation.
Record the weight of your sample, then set a small amount of the purified material aside for infra-red
analysis (1-2 drops).
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2. Characterization - IR spectroscopy
Obtain the infra-red spectrum of a thin film of the material – your instructor will show you how to do this.
Make sure that you have identified the frequencies of the major absorbance peaks on your infra-red
spectrum.
• The infra-red spectrum is usually collected in transmission mode – therefore absorbance is indicated
by troughs in the spectrum (% transmission < 100%), rather than peaks.
• The frequency of light in the infra-red spectrum is typically expressed in terms of wavenumbers (cm-1),
rather than the usual hertz (s-1). Wavenumbers are in fact reciprocal wavelength (1/λ) where λ is
expressed in cm, rather than m. It can be shown from the wave equation for light that reciprocal
wavelength is in fact proportional to frequency.
3. Characterization - Optical Rotation
Transfer the remainder of your material to a measuring cylinder, and make a solution of orange oil in
hexane. Calculate and record the concentration in your worksheet. Make sure that you wash all of the
orange oil into the flask (i.e. rinse your receiving flask with hexane, and transfer your rinses into the
volumetric flask before filling to the line).
Fill the polarimeter cell with this solution. The polarimeter cell is a long glass tube, with two screwtop end
caps (each end cap has a quartz plate to allow light to pass through the sample). Make sure that one end
is sealed before you transfer your material, and that both ends have a good seal before you place the
cell in the polarimeter. Our current cell has a path length of 0.5 dm (50 mm).
Measure the experimental optical rotation, taking note of the sign (+/- i.e. the direction) of the rotation,
and calculate the specific optical rotation.
Post Lab Report
Description of Results (6 points): Describe the observations from this experiment - see p6 for more
details. Specific points to note: What was the mass of product you recovered from your distillation? What
was the observed rotation and calculated specific rotation of your sample? What were the observed
boiling points of your two molecules? Note the important peaks that can identify your molecule on the IR
spectrum. Is your sample pure, or contaminated? How can you tell?
Analysis of Results (12 points):
1) (3 points) In no more than three sentences, describe the point of this experiment - why did you
perform a steam distillation to isolate your target compound, and how/why was it successful (or not)?
2) Analysis subquestions (5 points):
a) Orange oil is made up of a number of organic compounds, but only one (limonene) is predominant,
and is a liquid with specific optical rotation of +115.5°. On the basis of your value, is the orange oil pure?
b) Using your IR spectrum, what peaks are present for the important functional groups in limonene, and
what are those functional groups?
c) The boiling point of limonene is 176 ºC. You purified it by steam distillation, which allowed isolation at
lower temperature. Why was this successful (hint - look up the term "azeotrope")?
3) Critical analysis (4 points):
a) The natural enantiomer of limonene found in oranges is of the R configuration. (S)-Limonene is found
in pine oil - what would be the specific optical rotation of (S)-limonene? Why?
b) If your orange oil is not pure, describe another experiment you might perform to purify it further. How
might you check that you were successful?
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Final Exam Questions, Experiment 5
1) Which molecule is chiral?
2) How many chirality centers are there in this molecule?
3) Which atom is the chirality center in this molecule?
4) The specific rotation of R-(+)-limonene is [α]20D = +115.5°, concentration = 10% in ethanol. What is the
specific rotation of S-(-)-limonene under the same conditions?
a) +115.5° b) 0° c) -115.5° d) -65.2
e) cannot tell
5) The specific rotation of R-(+)-limonene is [α]20D = +115.5°, concentration = 10% in ethanol. What is the
specific rotation of R-(+)-α-phellandrene under the same conditions?
a) +115.5° b) 0° c) -115.5° d) -65.2
e) cannot tell
6) What are the correct configurations of the two stereocenters in the molecule below (from left to right)
under the Cahn-Ingold-Prelog rules?
7) The steam distillation of limonene occurs at temperatures much lower than its boiling point because
of the formation of this species, a liquid mixture whose vapor has identical proportions.
a) zoetrope
b) isotope
c) azeotrope
d) azimuth
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8) You isolate limonene from your orange peel via steam distillation, and measure the optical rotation.
Your sample has an optical rotation of [α]20D = +77.3°, but the literature value of R-(+)-limonene is [α]20D
= +115.5°. What is the most likely reason for the discrepancy?
a) The major product was S-(-)-limonene, not the R isomer.
b) The distillate was impure, and contains other molecules that have similar boiling points.
c) Limonene is not found in orange peel.
d) The literature value of the specific rotation is wrong.
9) The complete limonene extraction experiment is longer, and requires another distillation step after the
stream distillation to get completely pure limonene. Why?
a) The second distillation will separate the R and S enantiomers of limonene.
b) The steam distillation is a crude and unselective method of purification, and a number of other
similarly structured species are present in the distillate.
c) The second distillation is used to remove excess solvent.
d) The steam distillation does not separate limonene from citric acid and sugars in the orange
peel.
10) Here is an IR of another monoterpene, this one found in marjoram oil. Which one is it?
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Experiment 6: Bromination of trans-Stilbene
Reading: Solomons 12th Ed Chapter 8, especially pages 359-364 (olefin halogenation).
Introduction
In this experiment, you will perform the first of a number of reactions involving alkenes that we will cover
in the 008 series. You have covered the bromination of alkenes in lecture and discussed the
stereoselectivity of the process. Here you will do the reaction yourself.
Bromine is a highly corrosive liquid that fumes and is generally unpleasant to handle, so instead of using
bromine itself, you will use a surrogate reagent pyridinium bromide perbromide. This is a combination of
bromine, pyridine and hydrobromic acid that is a stable solid. In acetic acid solution, bromine (Br 2) is
reversibly released from this mixture and can react with a suitable alkene, in this case trans-stilbene (1,2diphenylethene).
Figure 1. Reaction Scheme.
Prelab Report
Objectives (2 pts): Describe the central objectives of this experiment. Describe one learning outcome
you expect to have gained at the end of this experiment.
Procedure (3 pts): In your prelab report, write an outline of the experimental procedure. Remember to
include your name, lab section and the name of your TA (on each page), and the title and number of the
experiment.
Chemical Table (4 pts):
1) Fill in the reaction table below. Make sure you correctly calculate the molar amounts of your reactive
materials.
name
formula
mol.-eq.
MW
mmol
amount
Stilbene
1.00
500 mg
Pyridinium Bromide
Perbromide
1.10
1.00 g
Glacial Acetic Acid
--
--
--
10 mL
product
2) What is the limiting reagent in this reaction?
Safety and Preparedness (3pts):
The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read
these and answer the following questions:
1) What is the greatest hazard posed by using glacial acetic acid?
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2) If you spill pyridinium bromide perbromide on your skin, what should you do?
3) What is the greatest hazard posed by weighing out pyridinium bromide perbromide?
Experiment
1. Reaction Setup
Into a 50 mL round-bottomed flask containing a magnetic spinbar and equipped with an air condenser,
weigh and place 500 mg of trans-(E)-stilbene. Transfer the flask to a sand bath on a magnetic stirrer.
(NOTE - clamp the flask joint, not the condenser!). Glacial Acetic Acid is corrosive and toxic - all
manipulations should be performed in the fumehood.
Using a measuring cylinder, add 10 mL glacial acetic acid to the flask and subsequently heat the flask
(with stirring) to 130 ºC until the solid dissolves (~5 mins). Raise the flask
from the sand bath (Caution - HOT!), remove the air condenser and leave
to cool for 5 mins.
Pyridinium Bromide Perbromide is a lachrymator (stings the eyes,
causes tears) - perform all manipulations in the fumehood.
Weigh 1.00 g of Pyridinium Bromide Perbromide and add the solid to the
reaction flask in one portion. Some perbromide may stick to the sides of the
flask - wash it down with some additional (no more than 5 mL) acetic acid.
Reattach the air condenser and lower the flask apparatus back into the sand
bath. Heat at 130 ºC for 10 min. The product should begin to precipitate out
during the reaction.
2. Isolation of Product
Remove the reaction flask from the sand bath and allow it to cool to ambient
temperature. Add 12 mL of water, with swirling, and then place the flask in
an ice bath for 10 mins. Collect the crystalline solid by vacuum filtration
using a Büchner funnel and side-arm flask. Wash the material with three 5
mL portions of cold water, then with two 2 mL portions of cold acetone. Dry
the product by leaving it on the filter and applying a vacuum.
3. Purification by Recrystallization
Figure 1. Schematic of
the reaction apparatus
Dissolve the solid product in a minimum amount of hot xylenes and then
allow to cool to room temperature slowly. Once recrystallization is complete, isolate the pure product by
vacuum filtration.
4. Characterization.
Weigh your purified product to determine the yield, and determine the melting point of your purified
product and compare it to the literature value. NOTE - SAVE your product. You may need it for next
week's lab experiment.
Post Lab Report
Description of Results (6 points): Describe the observations from this experiment - see p6 for more
details. Specific points to note: What was the mass of product you recovered from your reaction? What
was the yield of the reaction? What was the melting point of the product? Is your sample pure, or
contaminated? How can you tell?
Analysis of Results (12 points):
1) (3 points) In no more than three sentences, describe the point of this experiment, and how/why it
was successful.
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2) Analysis subquestions (6 points):
(a) Draw the mechanism of the reaction, using bromine (Br2) as your brominating agent rather than
pyridinium bromide perbromide.
(b) Why did you use pyridinium bromide perbromide instead of bromine?
3) Critical analysis (3 points):
a) Why is only one diastereomer formed in this reaction? Relate your answer to the mechanism you drew.
b) If you used cis-stilbene as your reactant, what would your products be?
Final Exam Questions, Experiment 6
1) What does it mean when you recover greater than 100% yield?
a) I am a demi-God that generates matter from nothingness. I demand immediate worship.
b) I'm bad at math and should re-calculate.
c) My material is impure. It most likely contains product plus residual solvent.
d) My TA told me the wrong answer.
e) There is more than one product of the reaction.
2) (E)-Stilbene can react with all the reagents below. However, one of the products is wrong - which one?
3) Only one of these reaction outcomes is correct. Which?
4) Which reaction outcome is correct?
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5) What are the correct configurations of the two stereocenters in the isomer of dibromostilbene drawn
below (from left to right) under the Cahn-Ingold-Prelog rules?
6) Only one of these reaction outcomes is correct. Which?
7) Which analytical method is NOT useful in distinguishing between molecules that are diastereoisomers?
a) Melting point measurement
b) IR spectroscopy
c) Thin layer chromatography
d) Boiling point measurement
8) The bromination of trans-stilbene was performed in the hood because:
a) glacial acetic acid is corrosive
b) bromine is a fuming, corrosive liquid
c) pyridinium bromide perbromide is a lachrymator
d) all of the above
9) You are performing the stilbene bromination experiment, and suddenly your eyes start burning and
you start tearing up uncontrollably. Which explanation is the most likely?
a) You moved your sample of pyridinium bromide perbromide out of the fumehood, and it is a
lachrymator.
b) You spilled xylenes on your glove.
c) You breathed xylenes vapor.
d) You spilled glacial acetic acid on your skin.
e) You moved your sample of stilbene out of the fumehood, and it is a lachrymator.
10) A student (obviously not you, must be someone else) does the stilbene bromination carelessly and
gets a second product from the reaction. Why might this have happened?
a) The glacial acetic acid was improperly stored and had a lot of water in it.
b) The pyridinium bromide perbromide solid has water in it.
c) Bromination is supposed to give these two products.
d) A second reaction happens in xylenes.
e) The pyridine in pyridinium bromide perbromide reacts with the stilbene.
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Experiment 7: Dehydrobromination of meso-Stilbene Dibromide
Reading: Solomons 12th Ed. Chapter 7, especially sections 7.7 and 7.13.
Introduction
In this experiment, you will react the product you made in last week's experiment (meso-stilbene
dibromide) with strong base in an elimination experiment. This reaction with yield an alkyne,
diphenylacetylene. The strong base you will use is potassium hydroxide. The second step of the reaction
is quite unfavorable, so you will strongly heat the reaction to allow conversion. This requires a high boiling
solvent, and you will use triethylene glycol.
Figure 1. Reaction Scheme.
Prelab Report
Objectives (2 pts): Describe the central objectives of this experiment. Describe one learning outcome
you expect to have gained at the end of this experiment.
Procedure (3 pts): In your prelab report, write an outline of the experimental procedure. Remember to
include your name, lab section and the name of your TA (on each page), and the title and number of the
experiment.
Chemical Table (4 pts):
1) Fill in the reaction table below. Make sure you correctly calculate the molar amounts of your reactants.
name
formula
mol.-eq.
MW
mmol
amount
Meso-Stilbene Dibromide
1.00
300 mg
Potassium Hydroxide
5.7
290 mg
Triethylene glycol
--
--
--
2 mL
product
2) Potassium hydroxide is hygroscopic. Will it be easy to weigh exactly 290 mg? Will the exact amount
of potassium hydroxide be critical to this reaction and why?
Safety and Preparedness (3 pts):
The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read
these and answer the following questions:
1) What is the greatest hazard posed by using potassium hydroxide pellets?
2) What is the difference between spilling solid KOH on your skin, and spilling a solution of KOH in
triethyleneglycol?
3) Why should you always monitor a sand bath with an external thermometer, as well as the temperature
recorded by the hotplate?
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Experiment
1. Reaction Setup
Into a 50 mL round-bottomed flask containing a magnetic spinbar and equipped with an air condenser,
weigh and place 300 mg of meso-stilbene dibromide and 290 mg of potassium hydroxide (Caution hygroscopic and corrosive). Using a graduated cylinder or, preferably, a large pipettor, add 2 mL
triethyleneglycol to the flask. Set a hotplate-magnetic stirrer to 500 °C (on the hotplate dial) and heat the
sand bath to 150 °C (as measured by the thermometer). Lower the hotplate to 190 ºC.
Transfer the flask to the sand bath (NOTE - clamp the flask joint, not the
condenser!) and heat (with stirring) for 10 min. The reaction mixture
should now be tan in color. Raise the flask from the sand bath (Caution
- HOT!), remove the air condenser, and cool for 10 min.
2. Isolation of Product
Remove the reaction flask from the sand bath and allow it to cool to
ambient temperature. Add 5 mL of water, with swirling, and then place
the flask in an ice bath for 15 min. Collect the crystalline solid by vacuum
filtration using a Büchner funnel and side-arm flask. Wash the material
with two 2 mL portions of cold 70% ethanol. Dry the product by leaving
it on the filter and applying a vacuum.
3. Purification by Recrystallization
Dissolve the solid product in a minimum amount of hot 70% ethanol and
then allow cool to room temperature slowly. Once recrystallization is
complete, isolate the pure product by vacuum filtration.
4. Characterization.
Weigh your purified product to determine the yield, and determine the
melting point of your purified product and compare it to the literature
value.
Post Lab Report
Figure 1. Schematic of the
reaction apparatus
Description of Results (6 points): Describe the observations from this experiment - see p6 for more
details. Specific points to note: What was the mass of product you recovered from your reaction? What
was the yield of the reaction? What was the melting point of the product? Is your sample pure, or
contaminated? How can you tell?
Analysis of Results (12 points):
1) (3 points) In no more than three sentences, describe the point of this experiment, and how/why it
was successful.
2) Analysis subquestions (6 points):
(a) Draw the mechanism of the reaction - note that there are two steps!
(b) Describe the role of KOH in this reaction.
3) Critical analysis (3 points):
(a) Why did you have to heat this reaction to such an extreme temperature? Use the mechanism you
drew as a hint.
(b) Which is the slow step - the first, or second?
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Final Exam Questions, Experiment 7
1) What are the mechanisms for the two steps of the following reaction?
2) Which is the correct INTERMEDIATE in the following reaction?
3) Why does the stilbene dibromide elimination require heating to such high temperatures?
a) Elimination to form alkenes is slow.
b) The second step requires a syn elimination of the H and Br to form the alkyne product, which
is unfavorable.
c) The second step requires an anti elimination of the H and Br to form the alkyne product, which
is unfavorable.
d) The first step requires a syn elimination of the H and Br to form the alkenyl bromide
intermediate, which is unfavorable.
4) What is the most favorable product of the following reaction?
5) What is the most favorable product of the following reaction?
6) What is the correct INTERMEDIATE in the following reaction?
7) What is the most favorable product of the following reaction?
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8) If you performed the elimination of meso-stilbene dibromide with potassium tert-butoxide at a
temperature that was too low to form the alkyne, what would be the most likely product formed?
9) The elimination of meso-stilbene dibromide was performed in the hood because:
a) Hot potassium hydroxide in triethylene glycol is highly corrosive.
b) meso-stilbene dibromide gives off bromine vapor.
c) meso-stilbene dibromide is highly corrosive.
d) KOH is a volatile liquid.
10) Why was triethylene glycol used as a solvent for the elimination of meso-stilbene dibromide?
a) It is a strongly basic solvent.
b) It is non-polar, so favors E2 eliminations.
c) It is a high boiling solvent which dissolves all the reactants.
d) It is a low boiling solvent which dissolves all the reactants.
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Experiment 8: Nucleophilic Substitution Reactions – Reactivity of Alkyl Halides
Reading: Solomons 12th Ed. Chapter 6, especially pp 262-272.
Introduction
The reaction rate of nucleophilic substitution reactions depends on two primary factors: substrate
structure and reaction conditions. In this experiment, we will investigate six representative alkyl halide
substrates and will compare their respective reaction rates under two sets of conditions. This will be
organized slightly differently than the other labs, and is an investigative lab experiment.
Sodium iodide dissolved in acetone is a useful reagent for determining the SN2 order of reactivity of the
alkyl halides above. Iodide anion is an excellent nucleophile, and acetone is a polar, aprotic solvent –
conditions that favor SN2 reactions. Sodium iodide is readily soluble in acetone, but sodium bromide and
sodium chloride are not, and will precipitate from the reaction mixture.
Silver nitrate dissolved in ethanol is a useful reagent for determining the SN1 order of reactivity of the
alkyl halides above. The Ag+ cation coordinates to a lone pair on the halogen atom. As a result, the C-X
bond is weakened, resulting in heterolysis of the C-X bond, and formation of a carbocation intermediate.
Ethanol promotes SN1 reactions because it is a highly polar, protic solvent, and stabilizes the formed
carbocation by solvation. As you may recall from General Chemistry, silver halide salts are highly
insoluble, and will precipitate from solution.
In each case, the amount of time required to see a change in a solution of alkyl halide upon addition of
either (a) sodium iodide, or (b) alcoholic silver nitrate, gives us a measure of how reactive each substrate
(alkyl halide) is under these different conditions.
Prelab Report
Objectives (2 pts): Describe the central objectives of this experiment. Describe one learning outcome
you expect to have gained at the end of this experiment.
Procedure and Chemical Table (4 pts): In your Laboratory Notebook, you should create two
experimental sections. Each section of the experiment should have a short description of the experiments
you will conduct (a synopsis) so that you can record your observations during the experiment. Create a
table for each experiment so that you can note the appearance of each reaction (12 in total) at 1 minute
intervals, both at room temperature and elevated temperature. Include the name, structure and formula
of all chemicals used in the experiment.
Also, answer the following two prelab questions:
1) The reaction of 2-chloropropane with sodium hydroxide can occur via both SN1 and SN2 mechanisms.
Draw arrow pushing schematics for each SN1 and SN2 mechanism for this reaction (2 pts).
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2) Draw the structure of the intermediate of the SN1 process, and the transition state of the SN2 process.
(1 pt).
Safety and Preparedness (3 pts):
The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read
these and answer the following questions:
1) Which of the alkyl halides in this experiment is most hazardous?
2) The most hazardous alkyl halide is a known carcinogen. What extra precautions should you take?
3) One of the alkyl halides is a lachrymator - what does that mean?
Experiment
Set up and stabilize a hot water bath at 45 °C.
1. Sodium Iodide in Acetone (SN2 conditions)
Label six clean, dry, small test tubes. Add 0.1 mL of one of the alkyl halides to each tube. Make sure to
note and keep track of which alkyl halide is contained in each tube. Keep your tubes in the hood to
minimize vapors in the lab. To each tube, rapidly add 1 mL of a 12% sodium iodide in acetone solution
in one portion, mix thoroughly, and record the beginning time. Watch the reactions and record the time
you first notice precipitate in each of the tubes. After 10 minutes at room temperature, place any tubes
that do not yet have a precipitate into the water bath. Make sure the temperature is not above 45 °C to
avoid evaporating acetone. After 10 minutes in the bath, remove the tubes and note any additional
samples with precipitate.
Beware of false positives! If any acetone evaporated during heating, some sodium iodide may have
precipitated on the walls of the test tube. Agitate the test tube for a few minutes to ensure that the
precipitate persists before recording a positive test. In the absence of precipitate notice any color changes
in the tubes.
Ultimately, you should be able to rank the alkyl halides from 1-6 in terms of SN2 reactivity.
2. Silver Nitrate in Ethanol (SN1 conditions)
Label six clean, dry, small test tubes. Add 0.1 mL of one of the alkyl halides to each tube. Make sure to
note and keep track of which alkyl halide is contained in each tube. Keep your tubes in the hood to
minimize vapors in the lab. To each tube, rapidly add 1 mL of a 1% silver nitrate in ethanol solution in
one portion, mix thoroughly, and record the beginning time. Watch the reactions and record the time you
first notice precipitate in each of the tubes. After 10 minutes at room temperature, place any tubes that
do not yet have a precipitate into the 45 °C water bath. After 10 minutes in the bath, remove the tubes
and note any additional samples with precipitate. Rank the alkyl halides from 1-6.
Post Lab Report
This is an investigative lab report, so the format is slightly different. Using your data from this experiment,
you will determine the factors that control the rate of SN1 and SN2 reactions of various alkyl halides. Your
final report should contain:
• Introduction – This section should introduce the background and purpose of the experiment.
• Experimental Procedure – This section should be complete and specific enough so that another organic
chemistry student could use your report to complete the experiment with similar results. Figures and
diagrams are useful in this section.
• Data/Results – This section should report your results as succinctly and clearly as possible. No
discussion is required and tables and graphs are useful ways to report data.
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• Analysis/Discussion/Conclusions – This section is the most important part of the report and is where
you convey that you understand the experiment and can interpret the data to make meaningful
conclusions. This section should be written in complete sentences and your analysis and conclusions
should be written clearly to convey your point.
In this section, consider the following questions:
a) Which alkyl halides were the most reactive under SN2 conditions? Which were the least reactive?
Explain the order of reactivity under SN2 conditions by considering alkyl halide structure, nature of the
leaving group, temperature, solvent, etc. Does the experimentally determined order fit what you
predicted? Account for any anomalous observations.
b) Which alkyl halides were the most reactive under SN1 conditions? Which were the least reactive?
Explain the order of reactivity under SN1 conditions by considering alkyl halide structure, nature of the
leaving group, temperature, solvent, etc. Does the experimentally determined order fit what you
predicted? Account for any anomalous observations.
Final Exam Questions, Experiment 8
1) Which of these alkyl halides cannot react via an SN1 mechanism?
2) Which of these alkyl halides reacts rapidly via both SN1 and SN2 mechanisms?
3) Which of these alkyl halides is essentially unreactive via either SN1 or SN2 mechanisms?
4) Which alkyl halide reacts fastest with sodium azide?
5) Which alkyl halide reacts fastest with silver nitrate in ethanol?
6) Which mechanism(s) is/are operating in the reaction below?
A)
B)
C)
D)
SN1 only
75% SN1, 25% SN2
50% SN1, 50% SN2
25% SN1, 75% SN2
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Chem 08LA Lab Manual
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7) Why can you analyze the reaction of alkyl halides with NaI/acetone or AgNO3/ethanol via visual
observation of a formed precipitate, rather than requiring spectroscopic analysis of the products?
a) Sodium chloride is insoluble in acetone, and silver chloride is insoluble in ethanol.
b) Sodium chloride is insoluble in ethanol, and silver chloride is insoluble in acetone.
c) Alkyl halides are insoluble in acetone and ethanol.
d) All sodium salts are insoluble in acetone and ethanol.
e) All silver salts are insoluble in acetone and ethanol.
8) Which of these hazards must be considered when using 1-chloropropene?
a) It is a high boiling solid.
b) It is a corrosive solid.
c) It passes quickly through nitrile gloves.
d) It is a known carcinogen.
e) All of the above.
9) You react your suite of alkyl halides with sodium iodide in acetone, and no precipitate forms in any of
them. What is the most likely explanation?
a) Iodide is a bad SN2 nucleophile.
b) All of the alkyl halides react via SN1 mechanisms.
c) The acetone is wet, and the NaCl precipitate has dissolved in the aqueous acetone.
d) Alkyl halides are bad electrophiles.
e) You heated the reaction too strongly.
10) You react your suite of alkyl halides with silver nitrate in ethanol, and you get a false positive: 1chlorobutane gives a precipitate. What is the most likely explanation?
a) Ethanol is a good SN2 nucleophile.
b) 1-Chloropropane reacts quickly via an SN1 mechanism.
c) Silver salts promote SN2 reactions.
d) The silver salt causes an elimination reaction to occur (as opposed to a substitution), which
also produces AgCl precipitate.
e) You didn’t heat the reaction enough.
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Chem 08LA Lab Manual
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ANSWERS TO FINAL EXAM QUESTIONS
Experiment 1
Q1
Q2
Q3
C
B
B
Q4
Q5
Q6
C
B
C
Q7
Q8
Q9
E
B
C
Q10
B
Q4
Q5
Q6
C
A
E
Q7
Q8
Q9
E
E
A
Q10
C
Q4
Q5
Q6
D
C
B
Q7
Q8
Q9
C
B
C
Q10
C
Q4
Q5
Q6
C
C
E
Q7
Q8
Q9
B
A
C
Q10
C
Q4
Q5
Q6
C
E
D
Q7
Q8
Q9
C
B
B
Q10
A
Q4
Q5
Q6
D
D
D
Q7
Q8
Q9
B
D
A
Q10
A
Q4
Q5
Q6
D
C
D
Q7
Q8
Q9
D
D
A
Q10
C
Q4
Q5
Q6
B
C
C
Q7
Q8
Q9
A
D
C
Q10
D
Experiment 2
Q1
Q2
Q3
C
D
D
Experiment 3
Q1
Q2
Q3
C
B
D
Experiment 4
Q1
Q2
Q3
D
D
D
Experiment 5
Q1
Q2
Q3
D
B
D
Experiment 6
Q1
Q2
Q3
C
B
E
Experiment 7
Q1
Q2
Q3
D
D
B
Experiment 8
Q1
Q2
Q3
D
B
D
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