Organic Chemistry Laboratory CHE 327
Addison Ault, Andrea Pionek,
Jeff Cardon, Charley Liberko
Laboratory
Information
Required:
Text: Addison Ault, Techniques and Experiments for Organic
Chemistry, 6th Edition. You should have the textbook with you in the lab at
all times.
Goggles may be purchased from the
stockroom for $5.00.
Carbonless notebooks may be purchased from the
stockroom for $9.
Daily Schedule
Each day we will meet at
Preparation
Before coming into the lab each day,
each student must be adequately prepared in order that the lab time is spent
safely and efficiently. Proper
preparation includes reading the lab procedure and relevant background material
(you may need to do this several times in order to understand it), and
preparation of the notebook with all necessary physical data (relevant melting
points, boiling points, densities, and solubilities).
Notebooks and reports
All data and observations will be recorded directly
in the notebook. The carbonless copy
from your notebook is due as you leave the laboratory each day or as soon as
you have finished collecting data for that experiment. Staple a copy of the Laboratory Notebook
Grading Rubric to your pages. Lab
reports, products, and extra credit questions are due at
Point Breakdown Points Approx. %
Notebook 130 19
Write-ups 260 37
Products 33 5
Quizzes 120 17
Final Exam 100 14
Technique 35
5
Other
22 3
Total 700 100
As
a general guide for grading, the following cut -offs will be used:
90% A- 80% B-
70%
C- 60% D-
Schedule
|
Day |
Experiment |
Reference (pages) |
Techniques / Reactions |
|
M 3 / 3 |
1.
Isolation of Acetylsalicylic Acid from Aspirin Tablets |
43-54,
150-159, 332-333 |
heating,
filtration, crystallization, melting points |
|
Tu 3 / 4 |
2.
Distillation of a methanol
/ water mixture |
62-72;
75-80, 305 |
Distillation |
|
W 3 / 5 |
3.
Separation of malachite green and phenolphthalein |
92-109 |
Acid
base extraction |
|
Th 3 / 6 |
4. Preparation of 2,4-Dinitrodiphenylamine |
475-476 116-119 |
Nucleophilic
aromatic substitution, recrystallization, TLC |
|
F 3 / 7 |
Quiz 1
|
|
|
|
M 3 / 10 |
5. Prep. of Cyclohexene from Cyclohexanol |
376-380 122-128 |
acid
catalyzed dehydration GC
analysis |
|
Tu 3 / 11 |
6.
Prep. of Cyclohexanone from cyclohexanol |
387-389 87-90 182-199 |
oxidation,
steam distillation, IR |
|
W 3 / 12 |
7. Preparation of “banana oil” |
417-426 |
Fischer
esterification, SN2
substitution |
|
Th 3 / 13 |
8.
Unknowns |
169-181 239-272 |
Solubility,
chemical tests for functional groups |
|
F 3 / 14 |
Quiz 2 |
|
Proposals
due for Expt. 12: 9:00AM |
|
M 3 / 17 |
9. Preparation of
tetraphenylcyclopentadieneone |
595-597 |
Aldol
reaction |
|
Tu
3 / 18 |
10.
Preparation of a photochromic compound |
564-566 |
electrophilic
aromatic substitution, nitration |
|
W
3 / 19 |
11.
Preparation of Malachite Green, Crystal Violet |
439-440 |
Grignard
reaction, preparation of dyes |
|
Th 3 / 20 |
12.
Student's Choice |
|
Proposals
due: Friday, March 14 at |
|
F 3 / 21 |
Quiz 3 |
|
|
|
M 3 / 24 |
13. Preparation of norbornene-2,3-dicarboxylic
anhydride |
507,
510-514 |
Diels-Alder
reaction |
|
Tu
3 / 25 |
Review,
Check out Pizza
Frenzy |
|
|
|
W 3 / 26 |
Final Exam 9:00 - Noon |
|
|
Safety
Keeping the lab safe is the number
one priority and it is everyone’s responsibility. Before you begin, read Section 1 in your lab
book. Several rules are worth repeating:
Eye protection
must be worn at all times in the lab.
Appropriate attire must be worn in the lab. Clothing
must cover all parts except the head, hands, and forearms. Long hair should be tied back.
Memorize the location of all exits, showers,
eye-washes, fire extinguishers, and fire blankets.
No food or beverages are allowed in the lab. Leave
backpacks and coats in the hallway.
Be certain that there are no flammables in the area
when lighting a flame. (Warning: artificial fingernails are extremely
flammable.)
Be alert for hazards in the lab. Do not proceed with any experiment until you
understand the hazards involved.
Report all injuries to your instructor, even if they
appear to be minor.
Do not come into contact with any of the solvents or
reagents used in this lab other than soap and water. Remove gloves and wash hands before leaving
lab.
Clean up all chemical spills immediately,
this includes drips on bottles.
Do not leave any bottle uncapped.
Dispose of all wastes as directed. (Ask before you dump.)
Come to the lab prepared.
Material Safety Data Sheets
(MSDS)
You have a right to be informed as
to all the known hazards and potential hazards of the materials you will work
with. MSDSs are provided by chemical
suppliers which describe risks and proper handling of the reagents you will
use. Copies of these forms are available
from the stockroom.
As an example, consider the MSDS for
acetone. Pay particular attention to the
“Precautionary Labeling” section. Each
compound is rated for its health, flammability, reactivity, and contact
hazards. The rating is on a scale of 0 (very low or nonexistent hazard) to 4
(extreme hazard). Acetone poses a low
health and contact hazard (rating of 1), it has a very low reactivity (rating
of 0), but severe flammability (rating of 3).
Keep in mind that you may already be familiar with acetone as it is
commonly used as a “nail polish remover”.
A few danger words that you should
get to know include:
Toxic - poisonous
Mutagen / carcinogen – causing mutations or cancer
respectively
Teratogen – (literally “monster-forming”) causing
birth defects
Lacrymator – causing watering of eyes irritation to
mucus membranes
Caustic – causing chemical burns
Grading
Guidelines
Notebooks
Each student must keep a notebook
with all data recorded immediately in ink. For each experiment, your notebook will be
graded on a 10-point scale. The work
should include the following, be in the order listed, and have the headings in
bold.
Pre-lab: To be done prior to
1 Descriptive title and date - This
is also the title that you should enter in your Table of Contents along with
the page numbers that the experiment is on.
2 Chemical structures / balanced chemical equations -Draw the structures for all organic reagents used
including solvents. Write a balanced chemical
equation for each reaction including acid/base reactions. Also include moles, masses, and/or volumes
required to perform the experiment and theoretical yield in a well organized
way. Refer to p. 30 in your text
book. Note: Equations in this manual are not balanced.
2 Data table of reagents
- Fill in a table with information for
all chemicals required in that particular experiment and their properties. (see Appendix 2-4 in this
manual)
1 Procedure reference - Write a bibliographic reference or references to where
the procedure can be found. Be
specific. Be sure you are including all
important parts of the procedure from the text and the Cornell lab manual. If you
prefer to write out procedure, you may.
During lab
1 Procedure summary as performed - Give a brief summary of the experiment including
chemicals used, lab techniques, and product analysis. Record anything that you performed
differently from the referenced procedure and all things unique to only your
experiment. If nothing was changed, make
a statement to that effect. This should
only be a couple of sentences or less and may be very similar to something
required in your formal report. (A good
way to refine your writing is to have to write something more than once.)
1 Qualitative observations during procedure - What do you see, smell, hear during
the experiment?
Post-lab
2 Results - This is a well-organized,
brief presentation of the results of your experiment. A table would work. When reporting measured physical data, include the
literature value with reference for comparison.
Include physical appearance,
melting point or boiling point, amount
obtained in grams and moles, theoretical yield and percent
yield in grams and moles with units and how they were calculated, limiting
reagent, and anything else specific to the final results of you experiment.
10 Total
Odds and ends- the following
may influence your technique points.
A copy of all spectra should be stapled into the notebook
behind that experiment. Spectra may be
photocopied and reduced or trimmed down to size if necessary to fit into your
report. Be sure to include a caption.
Notebooks will be collected Friday
mornings and at the final exam to be checked for table of contents and spectra.
Don’t forget to staple a grading
rubric to your notebook pages before you turn them in (See Appendix 5).
Reports
After the lab has been completed you will prepare a
short but formal report. These reports
should be word processed (hand drawing of structures is allowable if they are
done neatly) and are limited to two pages, excluding graphs and spectra. Text sections should be double spaced with
one inch margins and 12 point font. The reports
are due at
Experiment Number and Title
10% Claim – This statement
should lay claim to the results that you think you got (not what you were
supposed to have gotten). The claim is
essentially a conclusion and should typically include qualitative information on yield, quality, and purity of product.
20% Evidence – This
section must support the claim and will be a concise listing of what you did
and observed. All data (for example
number of grams and mmoles of reagents used, melting or boiling points of
products etc.) should be included here.
50% Discussion – This
section will convince the grader of the reasonableness of the claim in light of
the evidence. For maximum points, be
sure to include the any/all of the following when applicable:
a. A concise discussion
of any new technique and how this technique
relates to the particulars of the experiment.
b. A discussion
of yield (or recovery), including discussion of systematic losses due to the
limitations of the technique.
c. A balanced
chemical equation and a mechanism for
any reactions carried out in the labs.
d. Structures
for all reagents.
e. Spectra or
graphs with proper meaningful captions.
10% Visual Presentation – For maximum points, the report needs to
follow the required format, including title, section headings, and appropriate
length, be well organized and neatly presented.
10% Stylistic Presentation – For maximum points, the report needs to
be written using correct spelling, grammar, and references. There needs to be appropriate use of
significant figures. (Be warned: Good writing style will not make up for poor
or nonexistent content.)
Refer to the sample write-ups below. The samples are not shown with double spaces
text. Your reports should have double
spaced text. For the fun of it, what grade
would you give the first report? What
grade would you give the second? Has the
student forgotten anything in the first report?
__________________________________________
[Preferred Write-up]
Experiment 15
Isolation of caffeine from tea
Ben der Dunthat
Claim: A relatively pure sample of caffeine was recovered from black tea by extraction into hot water.
Evidence: The procedure was carried out as described by Ault[1] using 4 Lipton brand tea bags (11.6g), 120mL water, and 12.0 g CaCO3. The mixture was heated to boiling for 21 minutes and filtered by suction. After cooling the filtrate, the product was extracted into chloroform. Evaporation of the chloroform gave a white semisolid (0.47g) that was recrystallized from 95% ethanol (~3 mL) giving small colorless needles. 0.23g, 1.2 mmol, 1.8% isolated recovery, Mp 229-232, (235-236 lit.[2])
Discussion: Caffeine is an organic compound with a high degree of polarity and it is quite soluble in both hot water and chloroform. The high solubility in hot water (0.67g/ml) allows caffeine to be extracted from the tea leaves. The tannic acid in tea, however, is also water soluble and is extracted along with the caffeine. Since calcium salts of carboxylic acids are insoluble, the calcium carbonate acts to de-protonate the tannic acid and to precipitate it as the calcium salt making it possible to remove it by filtration. As the aqueous solution cools, the solubility of caffeine is greatly decreased allowing most of it to be extracted into the chloroform layer. Since caffeine is soluble in the cold water (0.02g/ml), the extraction will not remove all of the caffeine and some will remain in the aqueous layer. Caffeine has a reasonable solubility in cold ethanol (0.02 g/ml) and a fair amount would have remained in the ethanol solution after the recrystallization. The recovered yield is 1.8%, which compares to the reported range of caffeine in tea of 2-5%. The isolated compound melts over a three-degree range close to the reported value for caffeine showing it to be reasonably pure.
____________________________________________________________________________
[Less-than-desirable
Write-up]
Isolation of caffeen from tee
Sara N. Dipity
Claim: We made caffine from tea. We got it from the bags using isolation. The melting point was good.
First, we followed the proceedure and got caffene crystals. Then we preformed a recrystallization on our crystals. Then we dried our crystals. Then we weighed our crystals. They weighed .0032. A melting point was run on the crystals. The melting point on the crystals was 128o. This is not to bad.
We got cafeine from tea.... I don’t like tea unless its iced when its hot out and then it’s ok if you use lots of suger but not that pink stuff. We heated the water to make it more soluble. During the extraxion caffein was on top because its is organic. The sepertory funnell seperated the caffin because it is more poler. The calcium carbonate crystals looked like a white powder and their was some chunks in they’re: but I could have spilled some on the bench maybe. When I suction filtrated the crystals it took to long so more may have been lost. The calcium crystals were used because it is a base and it protonated the tannic so it is less soluble and it didn’t dissolve. I think that when I dried my stuff I let it dry two long so I lost some because some of it may have evaperated away. It is yellow and sticks to the vile and smelled like a keytone. It is mostly impure but more pure then my last product. My percent thearetical yeild was 4.27452% wich is not very good do to error. I wonder what would happen if we used instent tea instead. I think it would be more.
(Did you spot any errors? This could be worse. It could be hand scribbled and it could be three pages in length! Please don’t make us read anything like this.)
_________________________________________________
Answers to questions
Questions are presented for each
experiment to stimulate thinking about important concepts and should be
considered before writing your discussion.
The questions may serve as fodder for quizzes and exams. Answers to questions may be written on a
separate piece of paper and turned in for extra credit. Be sure to include your
name and the experiment number. Bonus
points will be given for answers to the questions as follows:
2 thoughtful,
correct answers
1 reasonable
answers
0 poor
or no answers
Extra
bonus points for exceptional work may be awarded at the discretion of the
instructor.
Product Labels
Each product should be properly
labeled and placed on the appropriate lab table with an accompanying
information card. The product vial
should contain a meaningful identification number containing the student’s initials
and notebook page number (i.e. CAL-43).
The accompanying card should contain the student’s name, product ID
number (matching the vial), product name, product amount (in grams), percent
yield (or percent recovery if appropriate) and measured physical data such as
melting or boiling point range. If a
spectrum was obtained, a labeled copy should be stapled to the card.
Product Quality
The quality of your products will be
graded on a three-point scale as given below:
3 High
yield, good quality
2 average
yield, average quality
1 poor
yield, poor quality
0 no
product
Technique
Your technique will be evaluated at
the end of the term and will be worth five percent of your overall grade. Technique points will be awarded at the
discretion of the instructors. The maximum
number of points will be awarded to students who:
-
Show up on time and are properly dressed
-
Are fully prepared for lab
-
Follow all safety rules
-
Perform laboratory functions safely and efficiently
-
Work carefully in the lab to avoid breakage, spills, contamination, and fire
-
Properly dispose of waste
-
Clean up their bench and common work areas daily
-
Overall quality and completeness of notebook
Time Management
It is expected that students will
come to lab fully prepared with major glassware setup in advance and will work
at a reasonable pace when in lab. All of
our experiments have been designed and tested so that they may be completed in
less than two and one-half hours if the student is adequately prepared. If for some unforeseen circumstance a fully
prepared student who works efficiently is unable to complete an experiment by
Describing your products
Science begins with observation. Communicating science must always include
descriptions of your observations. In
the organic lab, we must not only say that we obtained a product, but we must
be able to describe it. The most
fundamental distinction will be the phase of matter of your product; is it a
solid, liquid, or a gas? But that is
only the beginning; you should also describe its physical appearance and
properties. For example, if it is a
liquid, you should describe whether it is clear or cloudy (opaque). You should describe whether it is colored or
colorless. Note that clear and colorless
are two different properties. If you
obtain a solid you should describe its crystalline form; are the crystals needle-like,
platy, or prismatic? If the crystals are
too small to be observed they could be described as powdery. Smell is also an important distinguishing
characteristic; is the smell pleasant or pungent? Words to describe smells might include sweet,
fruity (esters), sour (carboxylic acids), fishy (amines), balsamic (cinnamon,
cocoa, vanilla etc.), camphoric, citrus (lemon or lime), floral or earthy to
name just a few.
Science is worthless without good
communication. When communicating, it is
important to spell and use words correctly.
The following are lists of words commonly misspelled or misused in this
course. Learn to use these words
properly.
Commonly misspelled words
Dye
/ dyed
Ketone
Perform
Precipitate
Separated
Separatory
funnel
Summary
Theoretical
Vial
Yield
Commonly misused words
Data
(a noun, plural)
Distillate
(the object; a noun)
Filter
(the action; a verb), Filter (the object; a noun)
Filtrate
(the material, a noun), (“Filtrated” will not be recognized in this course)
Precipitate
(the action, a verb), Precipitate (the material, a noun)
To
(a preposition), Two (a number), Too (an adverb)
Then
(for order in time), than (for comparison)
Their
(possessive form of they), There (a place), They’re (contraction of they are)
Experiment 1
Isolation of
Acetylsalicylic Acid from Aspirin Tablets
Read
pp. 43-54, 150-159, 332-333
Aspirin is an analgesic, an antipyretic, and an anti-inflammatory
agent. It was first produced
synthetically by Felix Hoffmann in 1893 and marketed by Bayer as a wonder-drug. Recently, aspirin has been marketed for its
ability to thin the blood and prevent or lessen the severity of heart attacks
and strokes. In this experiment, we
will isolate the acetylsalicylic acid from aspirin tablets.
Aspirin tablets contain acetylsalicylic
acid (the active ingredient) as well as “inert” binders to hold the tablet
together. We will take advantage of the
fact that acetylsalicylic acid is quite soluble in hot ethanol while the
binders are insoluble and can be removed by filtration. The solubility of
acetylsalicylic acid will be reduced by the addition of water to the solution,
allowing the acetylsalicylic acid to crystallize out.
Follow the procedure in the text for
isolating acetyl salicylic acid. After
allowing your product to dry overnight, determine its mass and melting point
range.
Report
Discuss the chemical principles used in this
lab. Be sure to record the amount of
product you obtained (recovered yield) as well as calculate the percent
recovery. The amount of acetylsalicylic
acid in each tablet is reported on the product label. In your discussion, include the theory of
purification by crystallization.
The following information may be helpful for this
experiment: Acetyl salicylic acid, M.W. 180.15 g / mol, pKa 3.49,
m.p 135 oC. Solubility: 1 g
acetylsalicylic acid dissolves in 300 ml water at 25 oC or 100 ml
water at 37oC, 5 ml ethanol, or 17 ml CHCl3.
Balances: Use only the top
loading balances in this course (not the analytical balances). If you spill on
a balance, consult with the instructor on how to clean it up. Never leave a
spill!
Water hoses: Keep your water
hoses for the entire term.
Melting points: Never leave the melting point apparatus “on” unless it
is in use. It could overheat and blowup
the thermometer.
Broken glassware: Put all broken
glassware in the bucket beside the waste basket. Remove and save any stoppers, stopcocks, or
plastic parts.
Clean-up: If detergent and water
are not sufficient to clean your glassware try rinsing with a small amount of acetone. If that
doesn’t work, try rinsing with dilute acid or base.
|
Substance |
Amount |
Properties |
sol. |
||||||
|
|
mmoles |
grams |
mL. |
M.W. |
dens.
|
m.p.
|
b.p. |
w |
o |
|
Acetylsalicylic
acid |
18 |
3.25 |
|
180 |
|
140 |
|
N |
Y |
|
Ethanol |
|
0.79 |
10 |
46 |
0.79 |
-130 |
78 |
Y |
Y |
|
Water |
|
50 |
50 |
18 |
1.00 |
0 |
100 |
Y |
N |
Experiment 2
Simple vs. Fractional
Distillation of a Methanol / Water Mixture.
Read
pp. 62-72; 75-80, 305
In this experiment you will perform both a simple
and a fractional distillation on a mixture of methanol and water and compare
the two techniques based on the composition of the distillate as a function of
the volume collected. While the goal of most distillations is to separate a
mixture of volatile substances by collecting them in separate containers, the
goal of these particular distillations is to compare the mole fractions of the
distillate as a function of volume collected for the two techniques. We will do this by monitoring the temperature
of the distillate and using the vapor diagram to relate temperature to
composition.
You will work with a partner, one will perform the
distillation and the other will record the data. You will trade duties for the second
distillation.
Prepare a 0.5 mole fraction methanol/water mixture
by combining 40 ml methanol with 18 ml water.
You will use this mixture for both distillations. After the first distillation, make the
necessary modifications in the glassware setup and pour the distillate back
into the boiling flask.
Fractional
distillation
For this experiment, we will modify a fractional
distillation apparatus in order to help us understand the role of the
fractionating column. (All future fractional distillations will use the
standard glassware set-up.) We will use two thermometers, one below the
fractionating column and the other in the standard place above the column in
the still head (connecting adapter).
This will allow us to monitor the difference in vapor composition in the
two regions of the apparatus. The lower
thermometer will be placed in the straight neck of a Claisen adaptor and
adjusted so that the bulb is just above the boiling liquid. The fractionating column will be placed on
the other neck of the Claisen adaptor.
When carrying out your distillation, record the volume collected and
temperature of both thermometers every 3-4 ml. Note whether or not any mixing
lines are observed as the distillate is being collected. Continue the
distillation until at least 50 ml distillate has been collected being sure to
stop before the pot runs dry.
On the same graph, plot the temperature of the
distillate (upper thermometer) (vertical-axis) vs. the volume collected
(horizontal axis) and the temperature of the vapor in the distillation pot
(lower thermometer). vs. the volume collected
You will be plotting the data from the next trial here too. Be sure to create a legend that distinguishes
between the three data sets. Be sure to
label the axes and give your graphs a meaningful title.
Simple
Distillation
Set up a simple distillation apparatus as shown on
page 66 with a flame used as the source of heat as shown on page 375. Collect the distillate in a graduated
cylinder. When carrying out your
distillation, record the volume collected and temperature every 3-4 ml. The
entire bulb of the thermometer must be in contact with the vapors when taking a
reading of the thermometer or the value will not be accurate; only take a
reading when liquid is being collected.
Note whether or not any mixing lines are observed as the distillate is
being collected. Continue the distillation until at least 50 ml distillate has
been collected being sure to stop before the pot runs dry.
On the same graph as above, plot the temperature of
the distillate (vertical-axis) vs. the volume collected (horizontal-axis). For
each recorded temperature, use the boiling point diagram p.73 to estimate the
mole fraction of methanol in the mixture being collected at each point. Plot the mole fraction of methanol vs. volume
amount collected. Be sure to keep the
scale of the volume axes the same from one graph to the next. How do the two
graphs compare? Is it reasonable to
simply use the boiling temperature of the distillate to monitor how well the
components have been separated?
Helpful
hints: 1) Do not use plastic clips or rubber
coated clamps on any parts of the distillation which will be heated with a
flame. 2) Be sure that all ground glass
joints are clean and properly fitted or the vapors may escape and catch fire. 3) Don’t forget boiling stones. 4) Never
distill to dryness.
Report
Discuss the theory of distillation
using your results as an example. Plot
your graphs side by side for easy comparison.
Explain the significance of your graphs, the temperature differences
between the two thermometers, and any other observations you made.
Questions: see question 1 a-e in the text on p.79 (consider the worst case scenario for each)
Glassware: Glassware is very expensive
so be careful when handling it. When
setting up your apparatus, never leave a piece of glassware hanging unsupported.
Never leave a piece where it can roll
off the counter.
Thermometers: Thermometers should be returned to the stockroom and
stored in an upright position to prevent separation of the alcohol column.
Experiment 3
Separation of
malachite green and phenolphthalein by acid base extraction
Read
pp. 92-109
In this experiment you will be given a mixture of
the indicator dyes malachite green and phenolphthalein. We will take advantage of their acid/base
properties to separate the mixture.
Phenolphthalein is commonly used in acid/base titrations and has the
pink color in basic solution familiar to many chemistry students. The compound is also a cathartic and was once
the active ingredient in “Ex-Lax” brand laxative. Malachite green in its solid form has a color
similar to the mineral known as malachite, CuCO3.Cu(OH)2. In strongly basic solutions a hydroxide ion
adds to malachite green giving a colorless (neutral) carbinol form. Malachite green is used to dye silk, wool,
leather, jute, and will dye cotton if a mordant is used. It has been used as a biological stain and as
a fungicide and parasiticide in fish.
Malachite green and phenolphthalein are acid / base
indicators and were chosen for this experiment so that it would be possible to
use the observed colors to keep track of what species are in each layer. This is a fairly new experiment and the
procedure has not been optimized. You
will work with a partner and explore the effect of one variable on the amount
and purity of the products. You and your
partner should work side by side performing each operation the same way and
choose one variable to change in the procedure.
Have the instructor okay your idea before you begin. Together, you will write one report.
Possible variations:
Use cresolphthalein instead
of phenolphthalein
Use Victoria Blue B instead
of malachite green
Vary the amount of oxalic
acid used to precipitate malachite green
Use different drying agents
in the ether prior to isolating the malachite green.
___________________________________________________________
Phenolphthalein
micro-extraction
This is a short exercise to demonstrate the effectiveness of a base extraction procedure.
The question you are intended to answer from the mini-experiment is: how many base extractions need to be done on an ether solution of phenolphthalein before the color is no longer detectable?
Place two milliliters phenolphthalein solution (0.1% in ether) in a test tube. Using a Pasteur pipette, extract the solution with a 2 mL portion of 5% NaOH solution. Be sure to mix the two layers thoroughly and allow them to completely separate. Using the pipette, remove the aqueous layer and place it in a separate test tube. Repeat until the pink color is no longer detectable in the aqueous layer.
Compare the colors of each of the successive aqueous extracts. What do they tell us about the effectiveness of the procedure?
____________________________________________________________________
Procedure
Be sure to note the observed colors
during the procedure and estimate the intensity of each color. Add 0.5 g of the dye mixture (0.3 g of
phenolphthalein and 0.2 g of Malachite Green) to 30 ml 3M NaOH in a separatory
funnel with mixing. Add 20 mL of diethyl
ether to the separatory funnel and mix the solvents slowly and thoroughly. Be sure to vent the separatory funnel
frequently. Drain off the aqueous layer through
the stopcock and decant the ether layer into a flask. Return the aqueous layer to the separatory
funnel and wash with two more 20 ml portions of ether combining all three ether
layers.
Phenolphthalein
The aqueous layer from above should
be filtered by gravity if any solid is present. Any remaining ether should be
removed with a pipette. Acidify the
aqueous layer by slowly adding 6M HCl (about 15 ml total will be needed). How will you know when the mixture is
acidic? Set the mixture aside to allow
the solid to form for at least 30 minutes preferably overnight. Collect the
solid by suction filtration using a Hirsch funnel, washing with a small amount
of water.
Isolation Malachite Green Oxalate
If the ether layer is not a single
phase (uniform and clear), be sure to remove any remaining water using a
pipette or a drying agent. Dissolve
0.16g oxalic acid in 10 mL of ether and add to the combined ether layers from
above (dissolution is slow so do this ahead of time). Note any color changes. Allow the mixture to precipitate for at least
30 minutes, preferably overnight. Collect
the product by suction filtration using a Hirsch funnel, and wash with a small
amount of ether.
Caution: Malachite green will stain your skin and
clothing.
Helpful
hints: 1) Label all flasks containing solutions. 2) Do not throw anything away until you have
the final products in hand. 3) Emulsions
may sometimes be broken by gently stirring with a glass stir rod or by sitting
for a few minutes. If the emulsion is
not easily broken in a few minutes just leave it in the separatory funnel and
go on.
Report
Discuss the principles of acid base extraction. Be sure to explain your observations for each
step. Relate colors to species present
and intensities to amounts of species present.
Questions
1) Calculate the pH of each aqueous solution in this
experiment.
a. 30 ml 3M NaOH
b. The original aqueous layer after 16 ml 6M HCl was
added.
2) a. A student proposed to separate this mixture
by using 20 ml 3M HCl and ether in the first step instead of the NaOH. How would this change the separation? What would be in each layer?
b. Assuming that the student was successful above,
what would the second step need to be to complete the separation? (hint: what
pH would the student need to obtain?)
Separatory funnels: Be sure to loosen the nut on the stopcock when
storing your separatory funnel or the Teflon will become distorted.
Pipettes: Pasteur pipettes
are disposable and should be put with the glass waste. The bulbs are reusable.
Experiment 4
Preparation of
2,4-Dinitrodiphenylamine
Read
pp. 92-109, 116-119, 475-476
Caution: Dinitrobromobenzene is an irritant, contact
with skin should be avoided.
In this experiment, we will prepare
dinitrodiphenylamine via nucleophilic aromatic substitution. We will perform the experiment on one-half
scale of that in the text. Continue to use
a 125 mL Erlenmeyer flask fit with a condenser for the recrystallization. Two
equivalents of the amine are needed to get the reaction to go; one does the
substitution and the other acts as a base.
As the reaction proceeds, the mixture will be set aside for one hour to
crystallize. During this crystallization
time, we will use thin layer chromatography to determine if the reaction has
gone to completion. After isolating our
product, we will purify it further by recrystallization.
Thin Layer Chromatography
(TLC)
We will use thin layer chromatography to follow the
progress of this reaction. We will
compare the TLC behavior of our product mixture with that of our two starting
materials. The visible disappearance of
one of the starting materials (limiting reagent) from the reaction mixture will
be taken as evidence that the reaction has gone to completion. In addition, we will explore the effect of
solvent polarity on Rf values.
The
procedure for thin layer chromatography is detailed in your text (pp-116-119)
and is summarized for this experiment below.
1) Prepare at least 3 micropipettes by heating
capillary pipettes in a flame and drawing them out.
2) Prepare at least three TLC plates by marking them
with a soft pencil as shown in the figure below.
3) Spot each plate with each starting materials and
the product mixture.
4) Elute one plate in hexane (non-polar), one in
acetone (most polar of the three), and one in toluene (intermediate polarity).
5) Use UV light to visualize each plate and mark the
location of the spots with a pencil.
After they have been marked, expose the plates to iodine vapors and note
any changes.
6) Using the eluting solvent that
gives the best separation of spots, run another TLC plate with the product
mixture after it has sat for an hour and note if there any differences from the
plate spotted with the fresh reaction mixture.
Make a scale
drawing of each plate in your notebook and record the measured Rf values.
Report
Discuss the chemical principles used
in this lab. Be sure to include a
mechanism for the reaction. In your
discussion, explain how the eluting solvent polarity affects the Rf
values for the substances. Also, make a
correlation between the relative Rf values of each compound and
their relative affinities to the mobile and stationary phases. A second part of your discussion should
include the theory behind recrystallization.
Marking plates for Thin
Layer Chromatography
Rf
= distance traveled by substance / distance traveled by solvent front.
Note:
avoid spotting compounds too close to the edge of the plate. Be sure that the spots are above the level of
the eluting solvent in the chamber.
Questions
1)
In previous years, the waste bottle from this lab developed a large mass
of long orange needles. What does this
tell us about our procedure? (be specific)
How could we fix this problem?
2) A student
ran out of bromodinitrobenzene and substituted chlorodinitrobenzene in the
reaction and found that the reaction with the chlorodinitrobenzene went
faster. Explain.
3)
After developing a TLC plate, a student observed that the plate had
dark spots running from the origin to the solvent front. What did the student do wrong?
Appendix 1 of this manual provides useful
suggestions for drawing reaction mechanisms.
Experiment 5
Dehydration of
Cyclohexanol to Cyclohexene
Read
pp. 376-380, 122-128
Use
caution when handling the phosphoric acid.
We will use a strong acid to
dehydrate an alcohol to obtain an alkene.
Le Chatelier’s principle will be used to explain why we were able to drive
the unfavorable reaction to completion. We will analyze both the crude and the
distilled products by gas chromatography.
In order to save time we will do our analyses as a group (by lab
benches) on mixed batches prepared by combining one drop from each student at
your bench. This will provide us with a
picture of the average purity for each bench.
If time permits, individual samples may be run after that. Prepare a 1% sample of your crude
cyclohexene in diethyl ether by combining one drop from each student (6 drops
total) and diluting that mixture down with 10 mL ether. Do the same for the purified cyclohexene. Your instructor will make the injections into
the GC. Compare the amount of
cyclohexene in the sample to the amount of cyclohexanol. The amount of ether in the sample is not a
controlled amount and we will ignore the height of this peak. Note that the
peak areas reported from GC run represent the amount of signal from the
detector not the number of molecules detected.
(The peak ratio between the ether signal and the cyclohexene signal does
not accurately reflect the mole ratio of the two.) We are assuming that molecules like
cyclohexene and the cyclohexanol are similar enough to have similar response
factors.
Helpful
hints: 1) Remember that it takes time to reach equilibrium so do not rush the
first distillation. 2) The collection
flask should be kept on ice. 3) Be sure
to save at least one drop of your crude material for GC analysis. 4) Before your final distillation, be sure
that your entire apparatus is clean and dry (and free from acetone
residue). 5) Collect your purified
product from your final distillation into a tared vial. 6) If your final product
becomes cloudy by picking up water, a small amount of drying agent can be used
to dry it (be sure to remove it before turning in your product).
Report
Discuss the chemical principles used in this
lab. Be sure to include a mechanism for
the reaction in your report. Your
discussion should comment on the purity of your product as determined by GC, the
equilibrium of the reaction, and how the reaction was brought to
completion.
Questions
1) Two
“distillations” were done during this lab.
What was the purpose of each?
2) Why was it critical to have the cyclohexene dry
and acid free before performing the second distillation?
3) If 2-methyl cyclohexanol were dehydrated, what
products would be expected? Which one
would be the major product? What technique
could be used to identify the products? Be specific.
Experiment 6
Cyclohexanone
from Cyclohexanol
Read
pp. 387-389, 87-90, 182-199.
Caution: Before you begin, check the actual
concentration of bleach on the bottle's label and adjust your amounts
accordingly.
Oxidations
are very important reactions in organic chemistry. While oxidations may look relatively simple
to perform on paper, in the lab they may become more complicated due to the
need to ensure the reaction has gone to completion and that the product is
adequately isolated. There are several
interesting features to this lab. Pay
attention to the purpose of each step as you read the lab. First, you will need to add the oxidizing
agent over a period of time in order to avoid having too large of a
concentration of poisonous chlorine gas at any one time. Our goal will be to maintain a steady state
concentration of our oxidant in order to avoid losing it as chlorine gas. Also, you will need to control the reaction
temperature to minimize the loss of Cl2 gas. As the reaction proceeds, the concentration
of cyclohexanol will decrease slowing the rate of the reaction while the
concentration of chloride will increase, increasing the rate of formation of
chlorine gas. You will need to check the
reaction mixture to ensure that excess oxidizing agent is present to ensure
that reaction has gone to completion.
After the reaction has been completed, the remaining oxidizing agent
will have to be destroyed to avoid over-oxidizing the product. Finally, the
product is insoluble in water and will be isolated by steam distillation before
being purified by regular distillation. Obtain
an IR spectrum of your product.
Helpful
hints: 1) It may be difficult to keep the reaction temperature under 35 oC
as stated in the lab text; use a water bath to keep the temperature at about 40
oC during the oxidation. 2)
After your final addition, be sure to give the reaction a few minutes to come
to completion before testing for excess chlorine. 4) It is much easier to purify your product
if the reaction has gone to completion.
Report
Comment on the purity of your product based on its
IR spectrum and its boiling range. Be
sure to include a mechanism for the reaction.
Discuss the chemical principles used in this lab including the
importance of each step in the procedure in obtaining the maximum amount of
product.
Questions
See
question 1 and 2 p.389.
3)
After you isolate the product, why is it necessary to neutralize the remaining
acetic acid? Be specific.
Experiment 7
Preparation of
Isoamyl Acetate
Read
pp. 417-426
Esters are an important functional
group, particularly for their flavor and fragrance properties. In this lab isoamyl acetate, a component of
banana oil (as well as an alarm pheromone of the honey bee) will be prepared by
two methods. One is an acid catalyzed
Fischer esterification, and the other is an SN2 substitution in a
polar aprotic solvent.
You will work in pairs for this
lab. One person will carry out the
esterification by the Fischer method (procedure 58.1) while the other person
will carry out the nucleophilic substitution (procedure 58.2). Pay attention to any color changes or
precipitate formation in these reactions.
Be sure to obtain an IR spectrum of your purified product in order to
determine its purity. Note that ~50 g
ice is the amount of ice chips that will fill a 100 mL beaker. Do not
weight the ice on the balance.
Report
Discuss the chemical principles used in this
lab. Be sure to include a mechanism for your
reaction. Propose what the most likely
impurities are in the sample based on your IR spectrum. In your discussion
compare the two methods used to prepare the ester.
Questions
1)
Consider equilibrium. Is one
esterification method more likely to bring the reaction to completion than the
other? Explain.
2)
Given that NaBr is much more soluble (>5X) in DMF than KBr explain why
potassium was a good choice for a counter ion in this reaction. How ill it affect the yield?
3)
A company wished to produce isopentenyl acetate, (3-methyl-2-pentenyl
acetate), the flavor known as “juicy fruit”. What would be the starting
materials in each reaction and what would be the likely products? Which esterification method would be better suited
to produce the desired product? (Hint: consider possible side reactions)
Explain.
Experiment 8
Identification of an unknown substance
Read pp. 169-181, 239-272, appendix
In this lab, you will use solubility and chemical
reactivity to determine the identity of two unknown compounds. You
will be given two vials containing unknown substances. These
are the only amounts that you will receive so guard them carefully. Be sure to protect them from spills and
losses due to evaporation. You will also want to make sure that you do not
squander your unknowns by using too much for any test or by running unnecessary
tests.
For the first unknown, you will be given the same
compound as your partner and you should compare results at every step. Repeat any tests for which your results do
not match. Once you have made a short
list of candidate compounds, you will report your results orally to one of the
instructors. The instructor will inform
you as to the actual identity of this unknown and give you advice on how to
proceed with your second unknown.
For your second unknown you will work alone and
write a formal report proposing a short list of possible matches for your
unknown and a way to distinguish between those if a derivative were to be
made.
Solubility
The solubility of a compound is an excellent
way to rapidly narrow down the number of possible functional groups that it
might contain. Using Section 23 of your
book as a guide, test the solubility of several known compounds as well as each
of your unknowns. Combine a few mg of
the compound (one drop of liquid) with a 3-5 mL solvent and note whether or not
the compound dissolved. Remember not to
use too much compound as you may saturate the solution or waste your unknown;
but you do need enough to be able to see it in the test tube. Check the solubility of the compound in
water. If the compound is soluble in
water check the pH of the aqueous solution.
If the compound is insoluble in water, check the solubility of your
compound in 5% HCl, and 5% NaOH.
Remember that the term soluble means that the solute and solvent form a
single phase; a single phase solution may be colored but must not be cloudy or
contain any precipitate or oily droplets.
Sometimes a compound is soluble but may go into solution slowly. Be sure that you allow enough time for each
to go into solution. The flow chart
below will help you make sense of your results.
Keep in mind that this chart is limited to the functional groups that we
will be testing in this lab.
Classification
tests
Chemical classification tests take
advantage of the fact that different compounds that contain the same functional
group have similar reactivity. You will
compare the reactivity of your unknown functional groups with compounds that
have known functional groups. The key to
success here is to always run a blank and a control and to carefully record
your observations. Also, as with any
test, the results should not be trusted if they are not reproducible. Be sure to repeat your tests if there is any
ambiguity.
Run a blank – run each test side by
side with a compound that will give a negative result.
Run a control – run each test side
by side with a compound that will give a positive test. By always having a positive and a negative
test alongside an unknown, the interpretation of the results will be more
straightforward.
Carefully record your observations
. When conflicting data is obtained, you
must decide what evidence should carry more weight. This is easier to do when you have
observations rather than just your interpretation. For example, it is more helpful, and more
correct to report that the Tollens test produced a gray precipitate on heating
for 15 minutes than to write down that the Tollens test was positive. Simply writing a ‘+’ sign in your notebook
may be misleading.
Before attempting any classification
tests on your unknowns, practice each test on known compounds to get a sense of
what positive and negative tests look like.
Results will inevitably vary each time the tests are run. Your observations may be different from those
reported in the book. Pay attention.
The recommended functional group tests are
summarized below not necessarily in the order that they should be run.
Helpful
hints: 1) Run a control and a blank side by side for each of the tests. These will help you interpret your
results. 2) If a result from a
classification test is ambiguous, it is usually quicker to repeat the test than
to try to interpret poor data.
Acetyl chloride
test for alcohols and amines (do this in the hood)
Cautiously add 3-5 drops of acetyl chloride to a dry test tube
containing a few mg unknown. Evolution
of heat and/or HCl gas indicates a positive test. It may difficult to determine the production
of a small amount of heat with a small amount of reactant. If your unknown is
less reactive it may a slightly larger amount of unknown to determine if a
reaction has occurred. Amines and
alcohols give positive tests but with noticeable differences. When the reaction mixture is carefully
diluted with water, a precipitate may form.
Alcohols often give a solid acyl ester and 1o and 2o
amines often give a solid acetaminde derivative; 3o amines do
not.
Test
|
Reference
|
Controls
|
|
Hinsberg
(Be sure to consult your instructor before attempting this test) |
29.2 |
Amines;
1o, 2o, 3o, (be sure to test an aromatic
amine as well) |
|
2,4-dinitrophenyhydrazine |
29.5 |
Aldehydes
and ketones |
|
Chromic
anhydride (run on alcohols and
aldehydes/ ketones) |
29.4 |
Alcohols;
(1o, 2o, 3o), aldehydes |
|
Acetyl
chloride |
Procedure
above |
Alcohols
and amines |
Amines
If
solubility indicates that the unknown is an amine:
Confirm the presence of an amine by
running the acetyl chloride test.
If an amine is present, consult your
instructor before attempting the Hinsberg test to distinguish 1o, 2o,
and 3o amines.
1o amines
will be soluble after step 1 and insoluble after step 2 of Hinsberg.
2o amines
will be insoluble after both steps 1 and 2 of Hinsberg.
3o amine will
not react and observations will reflect the solubility behavior of the
amine.
Aldehydes,
Ketones and Alcohols
If
solubility indicates that the unknown is an alcohol, aldehyde or ketone:
Test for the presence of an alcohol using acetyl
chloride.
If and alcohol is indicated, run chromic anhydride
test to distinguish 1o and 2o, from 3o
1o
and 2o alcohols will react quickly
3o alcohols give
no visible reaction.
If alcohol is not present run the
2,4-dinitrophenyl hydrazine test (+ for aldehydes and ketones).
If and aldehyde or ketone is
present, run chromic anhydride test (+ for aldehydes)
Carboxylic
Acids
We
will not use a positive test to confirm the presence of a carboxylic acid.
Determine
the physical characteristics.
There are clues to the compound’s
identity in its physical characteristics.
Is it a solid or a liquid? Does
it have a distinct color? Does it have a
characteristic odor?
Determine
a melting or boiling point range
If your unknown is a liquid
determine its boiling point by placing a small amount it in a Pyrex test tube
with a thermometer suspended a few centimeters above the liquid level. Using a flame and a wire screen gently heat
the tube until the reflux ring completely covers the bulb of the
thermometer. Be sure not to heat the
sides of the test tube above the liquid or you will superheat your vapor. Wait until the thermometer reaches a constant
temperature before taking a reading. We
recommend practicing this technique on one of the known compounds so that you
can look up the reported boiling point and check the accuracy of your result.
Choose
a derivative
With the information obtained above,
you should be able to go to the appropriate table in the appendix of your
textbook and make a short list of possible compounds. For example, if you have an ester with a
boiling range of 190-194 oC you could go to the table of esters and
choose esters that have a boiling point within a 5 -10 o range of
the observed value. Remember that your
value is a measured quantity and will have some error associated with it. In the table, there are three esters which
fall into that range: heptyl acetate, phenyl acetate and methyl benzoate. Since you cannot distinguish between these
based on your boiling point, you will need to consider a derivative. Note that of the three possible derivatives,
the DNB derivative is the best choice because the three possible compounds have
drastically different melting points with this derivative. The NBz derivative for two of the compounds
has the same melting point and it will not be helpful in distinguishing between
the two. The Acid derivative is not
even listed for two of the possible compounds so it is also not helpful in this
case. Due to time constraints, you will
not actually prepare these derivatives. Note that not all of the unknowns are
necessarily listed in the back of your text.
First
unknown Oral Reports.
After you have completed your work
on your first unknown, you will report your results orally to your
instructor. These reports will be graded
on a 10 point scale (3 points for being correct, 3 points for organization, and
4 points for logic). For your report,
you may only use your notebook as a reference.
Start by giving the unknown number and describing its physical characteristics
including melting or boiling point. Give
the results of the solubility tests and your conclusions based on
solubility. State the results of any
functional group tests you performed and conclude with the identity of your
unknown functional group and a short list of candidate compounds. State what derivative could be prepared and
how the results of that experiment would allow you to determine the identity of
the unknown compound.
Identification
of second unknown
For your unknown compound you will work
alone and follow the same procedure that you used to identify the first
unknown.
Report
Your report should include the
unknown number and the identity of the unknown functional group and a short
list of candidate compounds with all relevant data.
Leave the remainder of your unknown out on the
bench-top so that we can double-check it.
Experiment 9
Preparation of
Tetraphenylcyclopentadienone
Read
pp. 595-597
This lab utilizes a pair of aldol condensations
between dibenzylketone and benzil to produce tetraphenylcyclopentadienone. The product is unique for two reasons. First, the product is a deep purple
color. It is quite unusual for a
compound with such a short conjugation length to be so highly colored. Due to sterics, the phenyl groups are not in
the same plane as the cyclopentadienone ring and are not fully conjugated with
it. While cyclopentadienone is quite
reactive with itself toward Diels Alder reactions and it cannot be isolated on
its own, the bulky phenyl groups in the tetraphenylcyclopentadienone protect
the molecule from reacting with itself. This reaction is catalyzed by
base. The base used in this reaction
will be trimethylbenzylammonium hydroxide because it has a higher solubility in
our solvent than sodium hydroxide.
Prepare the compound on ½
scale as described in the text noting all color changes observed during the
procedure.
TLC
We will use thin layer chromatography as an
indicator of the purity of our product. Dissolve
a small amount of your product in dichloromethane and spot it on a TLC plate
along with each of the two starting materials.
Elute the plate with toluene.
Determine if either of the starting materials is present in the product.
Solid
phase IR
Obtain an IR spectrum of your dried product by
grinding ~10 mg compound with 10 mg KBr with a mortar and pestle into a fine
powder. Fill the sample compartment of
the specular reflectance attachment, level it smooth, and insert the sample
holder into the chamber.
Report
Discuss the chemical principles used in this
lab. Explain the color changes observed. Also, be sure to include a complete mechanism
for the reaction. (Since two identical
aldol reactions occur, you only need to show one complete reaction.) Discuss your results from the TLC and your IR
spectrum.
Questions
1) What did
you observe that would support the idea that the trimethylbenzylammonium
hydroxide is a catalyst in this reaction?
Explain
2) How does
your mechanism suggest that the hydroxide is a catalyst? (Start with the
definition of a catalyst.)
3) What is
the driving force for the removal of the water in this reaction?
Experiment 10
Preparation of
a Photochromic Compound
Read
pp. 564-566
Caution:
nitric and sulfuric acid can cause severe burns. Handle with care.
Follow
the beginning procedures in the book but
increase the amount of nitric acid to 2.25 mL of conc nitric acid (density
1.42 g/mL; 0.036 mole HNO3)
as two equivalents of the nitronium ion are needed for the complete
conversion.
One
of the goals of the experiment is to obtain your product as a single crystal. In
order to give yourself the best chance of doing this you must modify the last
part of the procedure. Here is the suggested modification:
First, filter the dried solution into a perfectly clean
125 mL, ground glass jointed, Erlenmeyer flask. Add one or two boiling stones.
Clamp the flask by its neck in position on top of the rings of a steam bath
that is supported above the base of the ring stand by a cork ring. The point is
to make it possible to remove the steam bath without disturbing the Erlenmeyer
flask. Complete a set-up for distillation of ether from the Erlenmeyer flask.
Now,
using the steam bath, distill slowly to reduce the volume of the dried ethereal
solution to 30 to 35 mL.
At
the point when 30 to 35 mL of solution remains, keep the Erlenmeyer flask
clamped in position while removing the condenser and distillation adapter. Then
slide the cork ring to the side so that
you can lower and remove the water bath. Don’t even think of removing the
boiling stones. Cover the neck of the flask with a piece of aluminum foil and
then allow the remaining solution to stand undisturbed until crystallization is
complete. If you are lucky it will take several hours to crystallize, and if
you are extremely fortunate you will obtain your product as a single crystal.
You then become a member of the 2-(2,4-dinitrobenzyl)pyridine Hall of Fame.
Helpful
hints: 1) Calculate out the number of
moles of all reactants and be sure that there is a slight excess of nitric
acid. 2) It may be easier to do the
extraction in several smaller batches rather than one large batch. 3) When distilling off the ether, reduce its
volume to 25 ml not 50 ml as it says in the book.
The
source of the photochromism in this compound has been the topic of debate. Here are the latest ideas on
structures.
“Apparently, while exposure of the ‘CH’ substance to light produces both the ‘OH’ and ‘NH’ substances, it is the ‘NH”’material that is responsible for the blue color.
CH OH NH
brown sugar brown blue
jeans blue
“ We could speculate that the deep blue color is a result of the effective resonance delocalization that is present in the NH form:
NH
form”
Journal of Chemical Education 2001, 78, 1596
Report
Discuss the chemical principles used
in this lab.
Questions
1)
Explain the regioselectivity of the nitration.
Why was only the one ring nitrated and why were those two positions
nitrated?
2) After the nitration, why was it necessary to add the base? What would have happened in the end if we didn’t add the base?
2-(2,4-dinitrobenzyl)-pyridine
Hall of Fame.
The Hall of Fame includes those students who have obtained their product primarily as a single crystal with a mass of 750 mg or more.
Current members are:
