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Chem 51LC Experiment 2 Report
EAS: Bromination of Aromatic Compounds
Instructions
Report scaffolds are provided to help you learn how to write about the experiments you
conduct. In 51LB you finished the last lab by generating your own experiment-specific
questions and answering them. Now you will begin to be responsible for writing a formal
lab report in paragraph format. For this post-lab, you will only need to write in paragraph
format for the introduction and theory sections. To assist you, the general questions to
consider when writing a lab report that were provided to you in 51LB have been
included below for those two sections. For the remaining sections of the post-lab
(results, discussion, conclusion), you must answer the experiment-specific questions
given below in italics. Do not write the specific questions in your separate document. Do
not include the general questions.
Be sure to also write this lab report following the Lab Report Guidelines handout
and use the rubric (located in the post-lab submission page) to ensure you are
touching on all of the relevant points.
Post-Lab Report Format: MUST BE TYPED IN WORD OR A SIMILAR PROGRAM,
NOT AN ELN PAGE! Times New Roman; 12 pt. font; double spaced; 1” margins; no
rd
more than 3 pages; use 3 person passive voice only (For example, “We dissolved the
white solid in 10 mL of hot water,” should be written as, “The white solid was dissolved
in 10 mL of hot water.”). Include your name, student ID number, and lab course code.
This format is NOT OPTIONAL. TAs will remove points for failure to follow instructions.
Purpose/Introduction
General Questions:
What experiment was performed? What were we trying to accomplish with this
experiment? How did we plan to accomplish this? The purpose of an experiment is not
simply to introduce a student to a technique or reaction!
Theory
General Questions:
Assume you are writing for another student who has taken organic chemistry before but
might have forgotten some of the details of reactions and lab techniques. What
information about the reaction and/or techniques being used in this experiment would
you need to remind them of to make sure they understand what you did, why you did it,
and what the results mean? What fundamental concepts were important in this
experiment? How do those concepts connect to the experimental procedure? Include
any relevant hypothesis you have regarding the results in this section. If there is a
reaction involved you should include a mechanism. Drawings of the mechanism should
be attached.
Results
NOTE: for your post-lab, your “individual reaction” will be the one performed in the
experiment videos. Your “individual” data will also be the one you gathered from
experiment videos. This is the only time you will use in-lab data for your post-lab.
What data were obtained by your entire class in this experiment? This
must be presented in a table(s). Select one representative data point for
each starting material. What product identities does each piece of melting
range data suggest?
What were the melting point, yield, and recovery of your individual
reaction?
In the appendix, include all class data in table form, and appropriate
calculations performed to obtain your individual data.
Discussion and Error Analysis
Explain why/how you chose the representative data points for each
starting material from the class data.
What reactivity order does the class data suggest? Explain.
What substitution order does the class data suggest? Explain.
What were your hypothesized reactivity and substitution orders?
Remember it is ok that these do not match your experimental results.
Were your hypotheses supported by the class data? If not, where did they
differ?
What is at least one problem you encountered or could have encountered
in this experiment? If you determine that no errors occurred, analyze a
potential error. What is your hypothesis to improve the problematic aspect
of the experiment and how would you test your hypothesis with an
analytical technique? What results from your test would support your
hypothesis? Why is it important to resolve this error?
Suggest a fix to the error and provide potential evidence to support the
claim that the error occurred and affected your results.
Conclusions and Future Experiments
What was the objective of the experiment? Was the objective met? Why or
why not? What specific data did you collect that support your conclusion?
Remember this is meant to be succinct; you do not need to re-explain your
results.
What experiment could you do in the future to verify the reactivity of the
four aromatic compounds if the reactivity order was not clear from the
class data?
03/10/19
Electrophilic Aromatic Substitution:
Bromination of Aromatic Compounds
REACTION: Electrophilic aromatic substitution
TECHNIQUES: Recrystallization, Melting point
In this experiment, you will brominate a variety of activated benzene derivatives. The
different substituents on the benzene ring are all activators and ortho, para-directors, yet
some of them are so strong as activators that they will result in di- or tri-brominated
products. The purpose of this lab is to determine the relative activating effect of the
substituents tested based on the products obtained in each reaction.
Four different aromatic compounds will be used in this experiment: aniline, acetanilide,
phenol, and anisole. You will perform a reaction using one of the four substrates, analyze
the melting point of the product you isolate, and then share your data with your class. You
should predict the substitution order. In other words, if multiple substitutions occur, which
substitution patterns do you expect (i.e. 2,4-disubstituted, 2,6-disubstituted, etc) You
should also predict the reactivity order (which substrates will brominate more than others)
BEFORE you perform the experiment. Be sure to justify your predictions. You should
include these predictions in your pre-lab work in your lab notebook and in the
Theory section of your written report.
Below is a table of all the possible products and their melting points.
Compound
MP
(°C)
Compound
MP
(°C)
2-bromoaniline
4-bromoaniline
2,4-dibromoaniline
2,6-dibromoaniline
2,4,6-tribromoaniline
32
66
80
87
122
2-bromophenol
4-bromophenol
2,4-dibromophenol
2,6-dibromophenol
2,4,6-tribromophenol
5
66
36
54
96
2-bromoacetanilide
4-bromoacetanilide
2,4-dibromoacetanilide
2,6-dibromoacetanilide
2,4,6-tribromoacetanilide
99
168
145
208
232
2-bromoanisole
4-bromoanisole
2,4-dibromoanisole
2,6-dibromoanisole
2,4,6-tribromoanisole
3
13
60
13
87
PRE-LAB ASSIGNMENT:
1. Complete all portions of pre-lab notebook work according to guidelines
2. Check that SDS files for all reagents are present in your SDS Files folder.
a. Add files for any missing compounds.
3. Give the hypothesized reactivity order with explanation in your ELN
4. Give the hypothesized substitution order with explanation in your ELN
5. Write a detailed procedure for the recrystallization
6. Complete Video Quiz(zes) on Canvas
7. Sapling assignment
8. Complete your pre-lab certification on Canvas
IMPORTANT SAFETY INFORMATION
● Pyridinium tribromide is corrosive and dangerous if absorbed through
the skin. Can cause eye damage. Avoid contact with skin and eyes.
● Glacial acetic acid is corrosive and has a strong, pungent odor. Use in
fume hood. Avoid contact with skin and eyes.
● Aniline, acetanilide, phenol, anisole, and all the brominated
derivatives are irritants. Wear gloves, and avoid all contact with skin,
eyes, and clothing.
● Ethanol and hexanes are flammable. Inhalation of vapors can be toxic.
Work in the fume hood and keep away from sparks or flames.
Experimental Procedure:
Reaction Set Up:
Add 1 mmol of your assigned aromatic compound to a 10-mL Erlenmeyer flask
equipped with a stir bar. Add 0.75 mL of acetic acid and stir the reaction mixture
until the aromatic compound is completely dissolved. Add 3 mmol of pyridinium
tribromide. Stir the reaction mixture at room temperature for 30 minutes.
Isolation of Product:
Quench the reaction by pouring it in a 25 mL Erlenmeyer containing 5 mL of
distilled water and 0.5 mL of saturated sodium bisulfite solution. Stir until the red
color disappears. This can take up to 5 min. Cool the solution in an ice bath for
10-15 min to cause the product to crash out. If no solid formation occurs, scratch
the insides of the flask to induce crystal formation. Filter the solid using a Hirsch
funnel and allow it to dry under vacuum for 10 min.
Purification and Analysis of Product:
Recrystallize the crude solid and obtain a melting range of the pure product. If you
started with aniline or acetanilide, use 95% ethanol for the recrystallization of the
product. If you started with anisole or phenol, use hexanes as the recrystallization
solvent.
Isolate the solid by vacuum filtration.
Analyze the recrystallized product to determine its identity. What data do you need
for this? What data should you record?
Collate Data:
Make sure you and your classmates enter your data into the shared class Google
sheet BEFORE you leave. Note that you are not working with anisole in lab but are
responsible for addressing its reactivity and substitution order in your post-lab.
What you need to know is that the product(s) of the anisole reaction is/are liquid at
room temperature.

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