Homework Problem Set 2 Iverson CH320N Due Friday, February 6 1

Homework Problem Set 2
Iverson CH320N
NAME (Print): _____________________________
SIGNATURE: _____________________________
Please print the
first three letters
of your last name
in the three boxes
1
Due Friday, February 6
Chemistry 320N
Dr. Brent Iverson
2nd Homework
February 2, 2015
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
We are trying something new here. This homework will be turned in on line. Go to the course canvas
site and look for the assignment, Homework 2. (Canvas calls this a quiz, but it is really just a
homework.) Click on that link. You will use this pdf as a guide to the problems, especially as a
reference for structures and spectra.
2
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
(1 pt. each) Circle all the statements relating to the theory of NMR that are true.
1. A changing magnetic field will cause charges to move.
2. A changing magnetic field will not cause charges to move.
3. Moving charge creates a magnetic field.
4. Moving charge does not create a magnetic field.
5. Electrons, neutrons, and protons are all charged.
6. Neutrons and protons are both charged.
7. Only electrons are charged.
8. Both electrons and protons are charged.
9. Atomic nuclei with an odd atomic mass or an odd atomic number have a quantum mechanical
property called spin.
10. The best way to the think about nuclear spin is as if nuclear postive charge (from the protons) were
circulating within the nucleus, thereby creating a small magnetic field that can interact with a strong
laboratory magnetic field.
11. 1 H and 13 C nuclei have a spin quantum number of 2.
12. 1 H and 13 C nuclei have a spin quantum number of 1.
13. 1 H and 13 C nuclei have a spin quantum number of 1/2.
14. The two spins states of a 1 H nucleus in a strong magnetic field are +1/2 and -1/2.
15. The two spins states of a 1 H nucleus in a strong magnetic field are +1 and -1.
16. The two spins states of a 1 H nucleus in a strong magnetic field are +2 and -2.
3
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
(1 pt. each) Suppose you place a sample of a molecule in a very strong laboratory magnetic
field. Circle the following statements that are true:
17. A magnetic field will cause the electron density to circulate in the molecule.
18. The circulating electron density will create its own magnetic field that is in the same direction as
the laboratory magnetic field.
19. The circulating electron density will create its own magnetic field that opposes the laboratory
magnetic field.
20. A 1 H nucleus with spin +1/2 will be lower in energy than an equivalent nucleus with a spin of -1/2
21. The difference in energy between +1/2 and -1/2 spin states for a given 1 H nucleus is directly
proportional to the strength of the external magnetic field.
22. If electromagnetic energy of the precise energy diffence between the +1/2 and -1/2 spins states is
used to irradiate the sample, the energy is absorbed as the spin "flips" from the +1/2 state to the -1/2
state.
23. "Resonance" in NMR refers to the phenomenon of absorption of energy when a nuclear spin "flips".
24. The magnetic field “felt” by any given nucleus in a molecule is actually the sum of (i) the external
magnetic field plus (ii) the magnetic field of the electrons around the nucleus plus (iii) the magnetic
fields caused by the different spin states of adjacent nuclei.
25. A 1 H nucleus surrounded by greater electron density feels a weaker net magnetic field (external
magnetic field plus the induced magnetic field from the circulating electron density) compared to a
1 H nucleus surrounded by less electron density.
26. A 1 H nucleus surrounded by greater electron density feels a stronger net magnetic field (external
magnetic field plus the induced magnetic field from the circulating electron density) compared to a
1 H nucleus surrounded by less electron density.
27. A 1 H nucleus surrounded by greater electron density is considered to be more shielded and comes
into resonance (absorbs electromgnetic radiation) at a lower frequency (smaller ppm).
28. A 1 H nucleus surrounded by greater electron density is considered to be more shielded and comes
into resonance (absorbs electromgnetic radiation) at a higher frequency (larger ppm).
4
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
(not graded) These two questions will not be graded, but turn them in anyway. They will help you
organize your thoughts regarding NMR and MRI. Something linke this might show up on the exam,
and that will be graded!
29. In no more than four sentences, explain what happens in a 1 H NMR experiment.
30. Suppose a relative of yours is having an MRI. In no more than four sentences, explain to them what
is happening when they have the MRI scan.
5
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
31. For this problem you need to ignore spin-spin splitting, in that we consider one signal to be derived
from one set of equivalent H atoms, regardless of splitting pattern. For each of the next three molecules,
on the lines provided state how many sets of equivalent sets of H atoms are present, next state how many
different signals will appear in the 1 H NMR spectrum of each, and finally, the relative ratios of the
integrations of the different signals (i.e. 1:2 or 1:2:6, etc.).
Number of
sets of equivlaent
H atoms
Molecule 1
H
H
H
C
H
C
C
H
H
H
C
H
H
H
Molecule 2
H
H
O
C
C
C
H
H
C
H
C
H
H
H
H
H
Molecule 3
H
H
H
H
C
C
C
H
H
C
H
H
C
H
H
6
Number of
different signals in
the NMR spectrum
Ratio of
signal
integrations
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
32. For the following molecules, state the number of peaks you expect in each 1 H NMR signal due to
spin-spin splitting.
Methylene 1
Molecule 1
OMethyl
CH2
H 3C
CH 3
O
Methyl 1
Methylene 2
Molecule 2
O
CH2
CH2
H 3C
Methyl 1
CH 3
Methyl 2
Methylene 1
7
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
33. For this question there are NMR spectra. The relative integrations are given above each
signal. Assign each spectra to the appropriate structure out of the following possibilities. Each
NMR spectrum has a letter on it. Choose the appropriate letter for each molecule. Notice that
not all of the molecules below will have an associated letter, as there are only seven spectra but
thirteen molecules. IF NO SPECTRA CORRESPOND TO THE MOLECULE, CHOOSE "N/A". You
didn't want us to make it too easy, did you? We recommend you print out the problems as the
spectra are easier to read when printed.
Molecule 1
Molecule 2 O
CH2
CH2
CH2
CH 3
H 3C
H
C
C
C
Molecule 4
O
CH 3
C
CH
CH2
CH 3
H 3C
CH
CH 3
H 3C
Molecule 7
O
CH
CH 3
C
H 3C
H 3C
CH 3
CH
CH2
CH 3
Molecule 5
CH2
H 3C
Molecule 6
CH 3
CH 3
CH2
H 3C
CH2
H 3C
CH 3
H 3C
Molecule 3
CH2 CH 3
CH2
CH2
C
HO
CH2
CH 3
H
Molecule 8
O
Molecule 9
H 3C
O
CH2
C
CH2
CH
CH 3
C
H 3C
CH 3
O
CH2
Molecule 10
CH 3
CH 3
H 3C
Molecule 11
CH2
HO
C
CH 3
H
Molecule 12
HO
H
8
CH
OH
C
O
C
H 3C
H 3C
CH 3
Molecule 13
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
A
3H
3H
2H
2
PPM
9
1
0
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
B
3H
3H
2H
4
3
PPM
10
2
1
0
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
C
3H
3H
3H
2H
1H
6
5
4
11
PPM
3
2
1
0
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
D
6H
1H
1H
3
2
PPM
12
1
0
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
E
6H
3H
2H
1H
2
PPM
13
1
0
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
F
3H
6H
2H
1H
2
PPM
14
1
0
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
G
9H
1H
2
PPM
15
1
0
Homework Problem Set 2
Iverson CH320N
Due Friday, February 6
34. For the following sequence of reactions, choose the answer that best describes the expected product
1. Mg°, ether
2.
O
Br
3. Mild HCl/H2O
racemic
Answer A
?
Answer B
OH
Answer C
OH
OH
OH
HO
HO
Answer D
Answer E
16