CHEM 223 Organic Molecules & Curved Arrow Mechanism Exam Practice

Chem 223 Summer 2019Mini Exam 4
Name _______________
Section_______
Student #___________
TA_________________
You have 60 minutes for this exam. It contains this cover sheet, 10 pages of
questions, and a separate formula sheet. You are allowed to use a molecular
model kit, but additional resources (no phones, calculators, etc.) You can answer
the questions in any order. My personal advice is to skim through the exam
initially and pick out questions you feel confident about, then work around to the
remaining questions. Also, keep in mind the point value for each question when
you allot time to each question.
Work should be shown for all questions, incorrect answers without any work will
not be awarded any credit, Likewise, showing your work drastically increases the
odds of you receiving partial credit.
Question
1
Points Possible
8
2
20
3
16
4
10
5
12
6
18
7
8
8
8
Exam extra credit
Q9
2
Total (100 For Q18)
100
1
Points Received
1) Draw the following organic molecules (8 pts)
(2 pts each, 1 pt for 1 error)
2
2) For each of the following compounds, how many 1H and 13C NMR signals will they
have? (20 pts)
a)
1
H
13
C
c)
1
H
13
C
b)
1
2
4
H
C
13
d)
1
H
13
C
5 or 6 (if cis/trans are different)
5
5
5
2 or 3 (if cis/trans are different)
2
Parts A-D 4 pts each, 2 pts for H and 2 pts for C NMR.
e)
Write the letters of the above compounds that will show a UV absorbance
above 200 nm?
f)
A, C
Write the letters of the above compounds that will show an M+2 peak in a
mass spectrum?
B, C
Parts E/F 2 pts each, 1 pt for each compound, -1 for any additional wrong compounds
3
3) Below is an organic compound will each position labelled. Fill out the following
table with NMR data about each position. For chemical shifts, you only need to
give an approximate value. If an entry doesn’t apply to that position, write “N/A”
(16 pts)
1
H chemical
shift (ppm)
1
1
1
C chemical
shift (ppm)
20
3
Triplet
2
30
2.5
2
Quartet
3
120
N/A
N/A
N/A
4
120
7
2
Doublet
5
120
7
2
Doublet
6
120
N/A
N/A
N/A
7
190
N/A
N/A
N/A
8
N/A
11
1
Singlet
Position
13
H integration
1
H splitting
Accept reasonable chemical shifts, within 1 ppm for H and 20 ppm for C.
2 pts each row: 2 pts for 0 mistakes, 1 pt for 1-2 mistakes, 0 pts for 3-4 mistakes
4
4) Answer the following questions using the spectroscopy data and formula given
below (10 points).
Formula: C11H12O2
1
H NMR: 7.4 (2H, doublet), 7.2 (2H, doublet), 5.6 (1H, triplet of triplets), 5.2 (2H,
doublet), 4.5 (2H, doublet), 2.3 (3H, singlet)
13
C NMR (DEPT): 209 (C), 139 (C), 132 (C), 130 (CH), 124 (CH), 118 (CH), 110 (CH2),
70 (CH2), 30 (CH3)
IR: 3080, 3020, 2920, 1690 (strong), 1650, 1620, no other peaks above 1500 cm-1
a) Based on the chemical formula, how many rings and/or double bonds are present
(2 points)? 6
b) From the IR and NMR, what functional groups are the O atoms part of (2 points)?
1 ketone, 1 ether (give credit for “1 ester”), 1 pt if they say “carbonyl” instead of
ketone
c) Does this molecule display any symmetry, why or why not? (2 points).
Yes because there are 11 carbon atoms, but only 9 peaks (they could make a similar
argument with the number of H peaks)
(1 pt “yes”, 1 pt explanation)
d) Using your answers to parts A-C, draw a structure for this compound (4 points).
Full credit for either of these structures. If not, partial credit as follows up to a MAX of 3
pts:
1 pt for correct formula
1 pt for correct functional groups (alkene + ketone + ether or alkene + ester)
1 pt for disubstituted benzene
1 pt for an allyl group
5
5) In each part of this question, you are given a series of 2-3 compounds and an
indicated spectroscopy. For each, briefly explain how you can use the indicated
spectroscopy to distinguish between those compounds (12 points, 3 points each).
(accept other reasonable answers)
1 pt for an answer that is incomplete, e.g. it only distinguishes 1 of the 3 compounds
a) (hint – all 3 compounds have MW = 122 g/mol)
Option 1 – use high resolution MS
Option 2 – look for an M+2 peak that is missing / 3:1 / 1:1
b)
Broad peak > 3000
No strong peak ~1700
No broad peak > 3000
No strong peak ~1700
6
Broad peak > 3000
Strong peak ~1700
c)
3 peaks
4 peaks
2 peaks
d)
Option 1: CH3 Singlet at ~3 ppm
Option 2: 1H septet at ~2 ppm
CH3 Singlet at ~2 ppm
1H septet at 3 ppm
7
6) What are the MAJOR product(s) from the following reactions, indicate stereochemistry where
relevant (18 pts)? (Parts A-D 4 pts each, part E 2 pts)
8
7) Design a synthesis of the following compound starting from (2E,5R)-5-bromohex2-ene and any inorganics and organics with 4 carbons or fewer. Pay attention to
stereochemistry! (8 pts)
Grade the synthesis holistically.
8 pts synthesis correct except for trivial errors
6 pts synthesis mostly correct
4 pts synthesis half correct
2 pts synthesis mostly wrong
0 pts synthesis fully wrong
9
8) Answer the following questions about some of the reactions we saw in chapter 12.
a) Draw the curved arrow mechanism for the following reaction shown below (4 pts).
Any reasonable base can be used in the final step.
2 pts intermediates, 2 pts curved arrows.
Give 2 pts total if they do an E2 mechanism instead of E1 since there isn’t a strong base
present.
10
b) Draw the curved arrow mechanism for the following terpene-forming reaction
shown below. You CAN abbreviate the pyrophosphate group as OPP. You do NOT
have to show the mechanism for the formation of the dimethylallyl cation. (4 pts).
(2 pts intermediates, 2 pts curved arrows)
9) What is your predicted score ___________________________ (2 pts)
11
Chem 223 Summer 2021
Mini Exam 4
By taking this exam, I acknowledge and agree to the following:
1. I certify that work in this exam is solely my work. I did not receive input from another individual.
2. I accept the consequences of academic dishonesty.
3. This exam is open-book and open-note and you may use a molecular model kit, but no other resources
are allowed.
Name
Student #
You have 60 minutes for this exam. You will take the exam using 1 of the 3 following options:
1. print the exam and complete it with a pen
2. write directly on the pdf file with your computer
3. write your answers on blank sheets of paper. These sheets MUST follow the EXACT same layout
as the exam – 1 cover sheet and then 9 pages of questions. You are NOT permitted to post this
exam on any website.
Regardless of how you take the exam, you will then convert your exam into a pdf file and upload it to
Gradescope by 2.35pm without penalty, gradescope closes at 3pm. There is a late penalty if the exam is
uploaded between 2.35-3pm. Exams must be uploaded as pdf files and must have the correct number of
pages, otherwise they will not be graded. You can answer the questions in any order. My personal
advice is to skim through the exam initially and pick out questions you feel confident about, then work
around to the remaining questions. Also, keep in mind the point value for each question when you allot
time to each question. Work should be shown for all questions, incorrect answers without any work will
not be awarded any credit, Likewise, showing your work drastically increases the odds of you receiving
partial credit. If an explanation question gives a sentence limit, please keep to that. There is a separate
formula sheet so please ensure you have the formula sheet at hand.
Question
1
Points Possible
12
2
20
3
16
4
32
5
12
6
8
Total
100
1
Points Received
1)
Draw the following organic molecules (12 pts)
Cis-1,4-dibromocyclohexane
(2R,4R)-2-bromo-4iodononane
(2S,3E)-2-bromo-oct-3-ene
(2S,3R,4S)-2,3-dibromo4-isopropyldecane
2
2)
For each of the following compounds, how many 1H and 13C NMR signals will they have? (22 pts)
a)
1
H
13
C
1
c)
1
H
13C
d)
1
H
13C
e)
b)
H
C
13
Write the letters of the above compounds that will show a UV absorbance
above 200 nm?
f)
Write the letters of the above compounds that will show an M+2 peak in a
mass spectrum?
g)
Write the letters of the above compounds that will show a broad peak above
3000 cm-1 in the IR
3
3)
In each part of this question, you are given a series of 2-3 compounds and an indicated
spectroscopy. For each, briefly explain how you can use the indicated spectroscopy to distinguish
between those compounds (16 points, 4 points each).
a)
(hint – all 3 compounds have MW = 122 g/mol)
b)
4
c)
using 13 C NMR
d)
using 1H NMR
5
4)
Answer the following questions about reactions (32 pts total).
i)
What are the MAJOR organic product(s) from the following reactions, indicate stereochemistry
where relevant. If there is no reaction write NR in the box (20 pts)?
6
ii)
Draw the curved arrow mechanism for the following reaction shown below (4 pts).
7
iii)
Draw the curved arrow mechanism for the biological elimination carried out on the following
compound (6 pts).
iv)
Explain what the role(s) the Histidine plays in the reaction above in part iii (2 pts)
8
5)
Answer the following questions using the spectroscopy data and formula given below (12
points).
Formula: C10H12O2
1
H NMR: 7.8 (1H, singlet), 7.7 (1H, doublet), 7.5 (1H, triplet), 7.3 (1H, doublet), 4.4 (2H, singlet), 3.2 (1H,
br.singlet), 2.3 (2H, quartet), 1.2 (3H, triplet)
13
C NMR (DEPT): 190 (C), 145 (C), 142 (CH), 135 (CH), 128 (C), 120 (CH), 117 (CH), 75 (CH2), 45 (CH2), 20
(CH3)
IR: 3300 (broad), 3070, 2930, 1700 (strong), 1600, no other peaks above 1500 cm-1
peak in H-NMR at 3.2 disappears with D2O shake
a)
Based on the chemical formula, how many rings and/or double bonds are present (3 points)?
b)
From the IR and NMR, what functional groups are the O atoms part of (3 points)?
c)
Does this molecule display any symmetry, why or why not? (2 points).
d)
Using your answers to parts A-C, draw a structure for this compound (4 points).
9
6)
Design a synthesis of the following compound starting from (the alcohol shown and any
inorganics and organics with 3 carbons or fewer. Pay attention to stereochemistry shown! (8 pts).
7)
pts)
What was your favorite and least favorite topic in chem 223?
10
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