UCLA Organic Chemistry Diastereoselective Lab & Chemical Reactions Lab Report: Chemistry Answers 2021

UCLA Organic Chemistry Diastereoselective Lab & Chemical Reactions Lab Report: Chemistry Answers 2021

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UCLA Organic Chemistry Diastereoselective Lab & Chemical Reactions Lab Report

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ONLINE ASSIGNMENT #5-WRITING A FORMAL LAB REPORT
1. Read and understand the Formal Lab Report guide on Canvas.
2. Write a formal report for the Diastereoselective lab. This will use the same basic procedure
and theory as the lab manual. Use the lab manual for the following:
1. title
2. introduction
3. relevant chemical reactions and structures
4. procedure
4. Use the data from the diastereoeselectivity lab shown below for:
5. data, observations, and calculations
6. discussion and conclusion sections
4. Don?t forget to include your 7. references
5. Data:
Page 30-Reagent Data Table:
3.51 grams of benzoin
35.00 grams of absolute ethanol
0.75 grams of sodium borohydride (NaBH4)
The substance and amount (grams/mL) are given, molar mass, moles and density needs to be
determined.
Page 31 Reagent Data Table:
3.05 grams of diol from week 1
25 mL of anhydrous acetone
4.00 mL of 2,2-dimethoxypropane
20 drops (0.6 mL) of sulfuric acid (H2SO4)
The substance and amount (grams/mL) are given, molar mass, theoretical yield and % yield needs
to be determined.
Page 31-Reagent Data Table 2:
3.05 grams of diol
2.59 grams of acetal
The substance and amount (grams/mL) are given, molar mass, theoretical yield and % yield needs
to be determined.
Page 32-Experimental value of the melting point of diol:
125-132oC
Page 32-Literature value of the melting point of diol:
132-134oC
Page 32-Experimental value of the melting point of acetal:
45-47oC
Page 32-Literature value of the melting point of acetal:
26-44oC
IR of (4R,5S)-2,2-dimethyl-4,5-diphenyl-1,3-dioxolane (acetal)
FORMAL LAB REPORTS
Introduction:
For the organic 1 and 2 labs at Wayne State, any mention of ?lab report? is actually referring to
the data sheets (from the lab manual) where students fill in their data, some observations from
the lab and answer any questions on those sheets.
However, usually a lab report refers to a formal lab report. A formal lab report is composed of:
1.
2.
3.
4.
5.
6.
7.
Title section
Introduction
Relevant chemical reactions and structures
Procedure
Data, observations, and calculations
Conclusion
References
In this exercise, students will learn about writing formal lab reports, proper ACS citation
guidelines and then write a formal lab report based on a hypothetical experiment and data.
Some of the information found in the following section comes from Xavier University of
Louisiana?s organic chemistry lab manual and class1.
What is the difference between data sheets, lab notebooks and formal lab reports?
Data sheets are sheets provided to the student from the lab manual. Data sheets are used to
record data and observations from the lab. Data sheets will provide some of the information
for the data section of a formal lab report.
Data sheets are provided to students before the students learn how to make their own
observations and discern what information is needed to be recorded from an experiment. A
data sheet is provided to help students realize what they need to record from their time in lab.
If it is on the data sheet, the student records it there. If it is not on the data sheet a student
does not record the information.
For example, if a lab procedure called for mixing around 2 grams of A with 3 grams of B in a
beaker with 25 mL of dichloromethane (DCM) for 50 minutes until the solution turned from
clear to red, below is an example of what the data sheet would look like:
Data Sheet for Lab
1. Weight of A
2. Weight of B
2.005 grams
2.982 grams
Compare that to the Lab Notebook:
Lab Notebook for Lab
As you can see there is much more information in the lab notebook.
How to Write a Formal Report (using the recrystallization experiment from organic 1 lab):
1.
2.
3.
4.
5.
6.
7.
Title section
Introduction
Relevant chemical reactions and structures
Procedure
Data, observations, and calculations
Discussion and Conclusion
References
There are 7 sections that go into a formal report. Sections 2-7 should have a title at the
beginning of the section (see below for examples). Using the
1. Title section:
Should include title of report followed by name, course, lab section and time, TA Name and
date of report. For example (in red):
Recrystallization1
Sean Hickey, CHM 1250-005, Wednesday 2:30 to 5:20 PM, TA Sara Worku
September 13, 2020
2. Introduction:
Should include summary of the theory of the experiment and the purpose of the
experiment. Note that the title of this section is included. For example (in red):
Introduction:
Recrystallization is one of the techniques used in organic chemistry lab to purify a
substance. In recrystallization, an impure organic compound is dissolved in a minimal
amount of solvent to dissolve the compound and impurities. The solution is cooled with
ice to recrystallize the compound leaving the impurities in the solvent. The crystals are
collected by suction filtration and analyzed for purity.
The purpose of this experiment is to recrystallize an impure unknown sample. After
recrystallization, the unknown is identified using mixed melting point.
3. Relevant chemical reactions and structures:
Should include any chemical reaction and/or any relevant structures. Note that the title of
this section is included. For example (in red):
Relevant chemical reactions and structures:
Potential known compound for mixed mp.
4. Procedure:
Should include the ideal procedure for the experiment. This would be your procedure
upload on Canvas but written in paragraph form with pictures. Note that the title of this
section is included.
Procedure:
Put your procedure upload in paragraph form with pictures
5. Data, observations, and calculations:
Should include all data (using table of reagents if the experiment includes chemical
reactions), observations and calculations. Unlike the procedure, which tells what SHOULD
happen in the experiment?this section tells what ACTUALLY happened in the experiment.
Note that the title of this section is included. For example (in red):
Data, observations, and calculations:
1.789 grams of unknown was obtained from the bottle marked unknown #1. The
unknown crystals were tannish colored, needle-like crystals. 50 mL of boiling water was
added to dissolve the crystals. The beaker was accidentally knocked over and the
experiment had to be restarted.
A new sample of 1.941 grams of unknown was obtained from the bottle marked unknown
#1. The unknown crystals were tannish colored, needle-like crystals. 55 mL of boiling
water was added to dissolve the crystals. After dissolving, a small amount of charcoal was
added and the solution was isolated using gravity filtration. The filtrate was cooled to
room temperature and then cooled on ice to produce a large amount of needle-like, white
crystals. The crystals were collected using suction filtration. After filtration, crystals were
left on the Buchner funnel as air was drawn through the funnel to dry the crystals.
A 50 mL beaker was weighed (after writing initials with grease pencil). The tare weight of
the beaker was 74.182 grams. The white crystals were allowed to dry for two weeks in the
equipment drawer. After two weeks, the beaker and dry crystals weighed 75.901 grams.
The crystals weighed 1.719 grams, and the percent recovery was 88.56%.
A fast melting point of the crystals determined that they melted somewhere around 130140oC. A more accurate melting point obtained a melting point range of 131-134oC. Based
on the melting point of the unknown, acetylsalicylic acid and t-cinnamic acid were chosen
as the possible unknown.
A mixed melting point was done with each known mixed with the recrystallized crystals.
Acetylsalicylic acid and unknown mixed together had a melting point range of 118-128oC.
t-Cinnamic acid and unknown mixed together had a melting point range of 132-134oC.
Based on the mixed melting point, t-cinnamic acid was determined to be the unknown.
% Recovery = (1.719/1.941) x 100 = 88.56%
6. Discussion and Conclusion:
Should include a summary of all the relevant results (not every piece of data but the
important data). Discussion of results should also be included. Note that the title of this
section is included. For example (in red):
Discussion and Conclusion:
A sample of unknown #1 was obtained and recrystallized with a percent recovery of
88.56%. A melting point of the purified unknown was taken and the range was 131-134oC.
Two chemicals with similar melting points were used to do a mixed melting point.
Acetylsalicylic acid (138-140oC) and the unknown produced a broadened and depressed
(lowered) melting point range of 118-128oC, indicating it was not the unknown. However,
t-cinnamic acid (134-135oC) and the unknown produced a very small, accurate melting
point range of 132-134oC, indicating t-cinnamic acid was the unknown.
Other than a spill that required a restart, the experiment proceeded without many issues.
The percent recovery of 88.56% was very good. The missing 11.44% was most likely due to
the initial impurities in the sample and some losses in the suction filtration. The mixed
melting point was very close to the literature value of the melting point of t-cinnamic
acid. The differences could be due to either some remaining impurities in the sample or
bad technique in taking the melting point.
7. References:
Any usage of copyrighted material or when information is obtained from any source other
than yourself, a reference must be made to indicate the source of information. For
example, if the melting point was not known for t-cinnamic acid and a website had to be
consulted to determine the melting point, then a reference to that website would need to
be included. For this experiment, the only reference is to the lab manual (note the
superscripted 1 next to the title of the experiment in section 1). The formatting for
references is based on the American Chemical Society Guide to Scholarly Communicationa
by Banik, et. al. Note that the title of this section is included. For example (in red):
References:
1. Zibuck, R. CHM 1250 Organic Chemistry Laboratory 1; Hayden-McNeil, 2019
LAB REPORT:
All 7 of these sections would be put together as a formal lab report. The report can be typed or
handwritten. If typed, some of the material (like pictures, structures) would have to be included
by inserting images or can be handwritten. If you used a picture from the internet or book, it
must be referenced (for example, if you cut and pasted a picture of suction filtration from the
internet, it must be referenced).
Hand-written structures, calculations and pictures may be drawn into a typed report (leave
spaces for putting these into the report).
Reference for the Style Guide:
a. Banik, G. M., Baysinger, G., Kamat, P., Pienta, N. ACS Guide to Scholarly Communication,
ACS Publications, 2020. DOI: https://doi.org/10.1021/acsguide
Reference for Organic 1 and 2 Lab manuals.
Zibuck, R. CHM 1250 Organic Chemistry Laboratory 1; Hayden-McNeil, 2019
Zibuck, R. CHM 2230 Organic Chemistry Laboratory 2; Hayden-McNeil, 2019
The formatting of different types of references based on ACS style guide are shown on the next
page.
A Problem in Diastereoselectivity:
Theory and procedure:
This lab focuses on the reduction of benzoin to a diol followed by conversion of that diol to an
acetal. Conversion to the acetal creates a product whose stereochemistry can be identified by
NMR. Once you know the stereochemistry of the acetal, you can infer the stereochemistry of
the diol, which CANNOT be identified using NMR.
FIRST WEEK:
The first week of the experiment will be the sodium borohydride (NaBH4) reduction of benzoin
to 1,2-diphenylethane-1,2-diol (hydrobenzoin). The reagents are added together and stirred to
form the diol product. Care needs to be taken with both the solvent (absolute ethanol, 100%
ethanol, no water) and the addition of sodium borohydride (NaBH4) since sodium borohydride
reacts vigorously both with any water in the solvent AND during conversion of the carbonyl to
the diol. The product of the reaction is acidified with 3M HCl, which will not only neutralize any
excess NaBH4 but also protonate the alkoxide to the diol. The diol forms as a white precipitate,
which is isolated using suction filtration and dried in your drawer over the week.
SECOND WEEK:
The dried product from your drawer is weighed and then an IR and mp is taken of the material
to confirm conversion of the ketone to an alcohol (look for the absence of ketone peaks in the
IR to confirm the full conversion of ketone to alcohol). 1 gram of the diol is then converted to
the acetal by adding anhydrous acetone, 2,2-dimethoxypropane and sulfuric acid (H2SO4)
dropwise to convert the diol to the acetal.
The acetone is the reagent that converts the diol to the acetal. What is the function of the 2,2dimethoxypropane in this reaction?
The product of this reaction is put in a sep funnel and excess acid is neutralized with sodium
carbonate (Na2CO3), which generates a significant amount of CO2 (venting of sep funnel is vital
in this neutralization). To this mixture is added 25 mL of diethyl ether and the organic layer is
isolated. The aqueous layer is extracted one more time with 25 mL of diethyl ether. The
combined organic layers are then put back in sep funnel and extracted twice with water and
then once with saturated sodium chloride. The organic layer is then dried with sodium sulfate
and decanted into a tared round bottom flask and the solvent is removed using the rotary
evaporator. After solvent removal, ice-cold pentane is added and then evaporated to isolate
the acetal. Weigh the round-bottom flask, calculate % yield for the two-step process and take a
mp and IR of the final product.
Safety concerns:
Per the lab manual, concentrated sulfuric acid and hydrochloric acid are dangerous chemicals;
proper PPE should be worn in the lab and all safety rules should be followed.
Why do I need to learn these techniques?
Almost every lab in organic 2 follows a similar procedure, a reaction is done, followed by isolation
(extraction) and characterization (IR, mp, TLC, NMR).
What do I need to do this week?
Preparation:
Read all the prelab material (manual, one pagers, supplementary material on Canvas)
Watch my diastereoselectivity video lecture and any other suggested videos or information
from Where can I find more information about??
Online Assignment:
Using the data on the next 2 pages, record all your data on the data pages and
answer all questions on those data pages, including interpretation of NMR
Complete the data sheets (pages 29-34) and answer the post-lab questions on page 5 of
this document.
Upload the data pages (pages 29-34) and the answers to the post-lab questions
to 23. Online Assignment 4-Diastereoselectivity Online Assignment Upload
DATA FOR DIASTEREOSELECTIVITY EXPERIMENT (data for data sheets in red):
Page 30-Reagent Data Table:
2.09 grams of benzoin
20.00 grams of absolute ethanol
0.41 grams of sodium borohydride (NaBH4)
The substance and amount (grams/mL) are given, molar mass, moles and density needs to be
determined.
Page 31 Reagent Data Table:
1.55 grams of diol from week 1
15 mL of anhydrous acetone
2.00 mL of 2,2-dimethoxypropane
12 drops (0.6 mL) of sulfuric acid (H2SO4)
The substance and amount (grams/mL) are given, molar mass, theoretical yield and % yield needs
to be determined.
Page 31-Reagent Data Table 2:
1.55 grams of diol
1.44 grams of acetal
The substance and amount (grams/mL) are given, molar mass, theoretical yield and % yield needs
to be determined.
Page 32-Experimental value of the melting point of diol:
125-132oC
Page 32-Literature value of the melting point of diol:
132-134oC
Page 32-Experimental value of the melting point of acetal:
45-47oC
Page 32-Literature value of the melting point of acetal:
48-49oC
IR of (4R,5S)-2,2-dimethyl-4,5-diphenyl-1,3-dioxolane (acetal)
Name:
TA Name:
Diastereoselectivity Post Lab Questions
Section:
1. Provide the products for the following reactions (6 points, 3 points per question).
O
OH
NaBH4, Methanol
O
O
OH
H+
OH
2. Draw the mechanism for the following (9 points).
O
OH
NaBH4, Methanol
3. Draw the 1H-NMR for the reduction compound below. Make sure to include integration of
beach peak. Label each peak on the NMR to match your product (10 points):
OH
B
A
5
4
3
C
D
F
E
2
1
0

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