Quizzes and Results from an
Organic Chemistry Molecular
Modeling Study
American Chemical Society
New York City
September 11, 2003
Jim Hermanson & Julie B. Ealy
Penn State University
Berks-Lehigh Valley
1
Quiz #1
On structure A
the arrow is
pointing to a
nitrogen
On structure B,
the arrow is
pointing to a
nitrogen
On structure
C, the arrow
is pointing to
an oxygen
1. Which of the structures are aromatic?
A. B, C
B. A, B
C. A, B, C
D. A, C
2. Fill in the missing electron pairs on the nitrogens or oxygen on the three
structures making sure to position them so that they support your
choice in Question 1.
3. Explain your choice of electron pairs on Structure C.
2
Results from Quiz #1 – Aromaticity (1 & 2)
Question 1: Which of the structures are aromatic?
31.6% - correct answered
68.4% - incorrect answer
Answer
A
B
C
D
# of students
3
5
6
5
15.8
26.3
31.6
26.3
%
Question 2: Placement of electrons on N or O to support choice in Question 1.
% Correct
# of students
Comments
26.3
5
Choice correct; electron placement correct
15.8
3
Choice incorrect; electron placement supported
choice
31.6
6
Choice correct; some electron placement correct
26.3
5
Choice incorrect; electron placement incorrect
In addition to incorrect placement of electrons, the following incorrect answers were
seen supplied by students:
1. no electrons
2. (+) sign on the oxygen or nitrogen
3. Presence of a p-orbital with or without electrons
4. Placement of hydrogen on nitrogen or oxygen and no electrons
3
Results from Quiz #1 – Aromaticity (3)
Question 3: Explanation of pairs on structure C.
36.8% (7) Correct
63.2% Incorrect
Example responses
Correct Explanation:
36.8%(7 students)
1) …2 [oxygen electrons]are in the system for aromatic and 2 are on the
oxygen only.
2) Structure C has an electron pair with a set outside of the ring and inside
the ring, therefore making it aromatic.
Not a correct explanation for the question asked or incorrect:
10.5% (2 students) Valence electron explanation:
Oxygen has 6 valance electrons and two are used. So 4 others have to be
placed.
31.6% (6 students)
Octet explanation:
1) …2 electrons are placed on the oxygen to complete the octet.
2) Oxygen should have 4 pairs of electrons. Octet rule.
10.6% (2 students)
sp3 explanation:
The molecule will not have sp3 bonding at the site if the electrons are
positioned in this manner (2 electrons inside and 2 electrons outside).
10.6% (2 students)
Miscellaneous explanations:
The electrons on the top and bottom. The electrons need to move easily
around the ring. (Both electrons outside on the oxygen).
4
Quiz #2
A
Black-carbon
Red-oxygen
B
Green-hydrogen
C
D
Yellow-fluorine
Blue-nitrogen
1. Rank the molecules in order from the most shielded methyl protons to the
least shielded methyl protons.
Most shielded
Least shielded
2. Rank the molecules from farthest downfield to farthest upfield.
Farthest downfield
Farthest upfield
3. Explain the rankings in question 1.
4. Explain the rankings in question 2.
5
Results from Quiz #2 – Shield/Deshield (1)
Question # 1: Rank the molecules in order from the most shielded
methyl protons to the least shielded methyl protons.
Most shielded
Least shielded
Correct answer was ADBC
73.7% Correct
26.3% Incorrect
Though a large percentage of students answered this question correctly it
would be more revealing if the molecules consisted of different atoms as
follows:
1) As a series of halogens + the methyl group following a family trend), or
2) Atoms bonded to a methyl group where the atoms used move across a row.
Answer
# of students
%
ADBC
ACBD
ABDC
DBCA
ACDB
14
1
1
2
1
73.7*
5.26
5.26
10.5
5.26
6
Results from Quiz #2 – Shield/Deshield (2)
Question #2: Rank the molecules from farthest downfield to
farthest upfield.
Farthest downfield
Farthest upfield
Correct answer CBDA.
63.2% Correct
Answer
# of students
%
36.8% Incorrect
CBDA
DBCA
ACBD
CABC
BDCA
ACBA
CDBA
12
1
1
1
1
2
1
63.2*
5.26
5.26
5.26
10.5
5.26
5.26
*It’s notable that a number of students (about 10%) got the first
question correct, but failed to see that the answer to the second question
is just the reverse of the first answer-- as predicted by theory taught in
lecture. It might be instructive to have asked the second question
designed to keep the answer in the same order as that of question # 1,
ranking from farthest upfield to farthest downfield.
7
Results from Quiz #2 – Shield/Deshield (3)
Question 3: Explain the rankings in Question 1 – most shielded
methyl protons to least shielded methyl protons.
I. 52.6% (10 students) Correct multiple choice order – Satisfactory explanation:
Correct explanation required a proper usage of electronegativity theory as
applied to the deshielding phenomenon exhibited on the molecule.
Minimum explanation; Electronegative elements deshield nearby
(vicinal) protons.
Best explanation: Fluorine is the most electronegative atom in this
series, hence it pulls electron density toward itself and away from nearby
(vicinal) protons; in the process, deshielding these same protons. Oxygen-being the second most electronegative element--generates the second
highest level of deshioelding on nearby protons. Nitrogen is the least
electronegative and exhibits the least amount of deshielding effect on
nearby protons. In ethane, the electronegativities of hydrogen and carbon
are roughly the same, therefore, no--or very little-- deshielding of vicinal
protons occurs.
II. 21.1% (4 students) Correct multiple choice order – Unsatisfactory
explanations:
Explanations included:
1) Simply stating“electronegativity”
2) Stating that the more polar the molecule, the greater the deshielding
3) Stating that it depended on how much the surrounding molecules tended to
deshield hydrogens around them (wrong use of chemistry language)
4) Unpaired electrons from the oxygen, nitrogen and fluorine cause the
surrounding protons to be more deshielded. The more unshared pairs, the more
deshielded (also drew lone pairs on O, N, and F)
8
Results from Quiz #2 – Shield/Deshield (3)
III. 26.3% (5 students) Incorrect multiple choice order – Unsatisfactory explanation.
Example explanations:
1) In molecule A electrons are being pulled towards hydrogen, making it the most shielded
whereas in the other molecules they are being pulled towards the heteroatoms.
2) Because the oxygen will absorb or withdraw the electrons from methyl groups.
3) The more protons are pulled from hydrogens, the higher the shielding
9
Results from Quiz #2 – Shield/Deshield (4)
Question 4: Explain rankings in Question 2 – farthest downfield to
farthest upfield
57.9% (11 students) Question #2 ranking correct; satisfactory explanation:
Explanations:
1) Deshielding gives a downfield shift; shieldeding gives an upfield shift
2) Least shielded or deshielded/downfield
3) C-H molecule A farthest upfield, then N, O, and F
5.26% (1) Question #2 ranking correct; incomplete explanation:
Explanation:
Electronegativity/backwards
10.5% (2) Question #2 ranking incorrect; unsatisfactory explanation:
Explanation:
1) The more downfield, the more deshielded – bulkier groups are more
shielded, which should also be taken into consideration.
2) O and N will appear about the same region on a spectro plate
21.1% (4) Question #2 ranking incorrect, though, reverse of Question 1;
satisfactory explanation:
Explanation:
Deshield/downfield
5.26% (1) Question #2 ranking incorrect, though, reverse of Question 1;
unsatisfactory explanation:
Explanation:
Question 2 is just asking the opposition of Question 1.
10
Quiz #3
Structure A
Structure B
1. On Structure B there are how many unique carbons?
A. 2
B. 4
C. 6
D. 8
2. On Structure A there are how many equivalent sets of hydrogens?
A. 1
B. 2
C. 3
D. 4
3. Describe the equivalent sets of hydrogens on Structure A. Also identify the
equivalent sets of hydrogens by number.
11
Results from Quiz #3 – Unique C/H (1 & 2)
Question 1. On Structure B there are how many unique carbons?
Correct answer was choice D (8)
26.3% Correct
73.7% Incorrect
Though only 26.3% of the students answered the question correctly it is
recommended changing the choices to 4, 5, 6, and 8 carbons instead of 2, 4, 6,
and 8 carbons
# of unique carbons
2
4
6
8
# of students
1
8
5
5
% of students
5.26
42.1
26.3
26.3
Question 2. On Structure A there are how many equivalent sets of hydrogens?
Correct answer was choice C (3)
73.7% Correct
26.3% Incorrect
# of equivalent sets
1
2
3
4
# of students
0
4
14
1
% of students
0
21.1
73.7
5.26
We recommend changing the choices to 2, 3, and 4, not 1, 2, 3, and 4.
12
Results from Quiz #3 – Unique C/H (3)
Question 3. Describe the equivalent sets of hydrogens on Structure A. Also
identify the equivalent sets of hydrogens by number.
68.4% Correct
26.3% Incorrect
5.26% No response
Correct responses:
A. Students either drew an axis of symmetry or there was a statement about an
axis.
Example responses:
1) Axis of rotation and 3 sets of hydrogens
2) Hydrogens on each side of the double bond can be rotated into each
other
3) The equivalent hydrogens fall on equivalent carbons. By symmetry
across the axis, those are equivalent.
B. Students either listed the equivalent sets of hydrogens by number or circled
them.
Incorrect responses:
21.1% (4) of the students had a similar incorrect response.
Example response:
Equivalence set one is composed of hydrogen attached to carbons 4, 3, 2,
and 1 and set two is the two hydrogens attached to carbons 5 and 6.
5.26% (1) of the students had the response.
2 of the 3 sets were correct - 1, 4 and 2, 3
Instead of 5, 6 as one equivalent set, they were separated into two different
sets.
13
Quiz #4
A
B
C
D
1. The structure that fits with the attached spectroscopic information is (circle
your choice)
A
B
C
D
2. Explain how your choice was made.
14
Results from Quiz #4 - Spectroscopy
Question 1. The structure that fits with the attached spectroscopic
information is (circle your choice)
A
B
C
D
Correct answer was choice B (15)
88.2% correct
11.8% incorrect
A
B
C
D
# of students
0
15
1
1
% of students
0
88.2
5.88
5.88
Structure
Question 2. Explain how your choice was made.
(The percentages do not total 100%. A student’s responses were included in more
than one category.)
47.1% (8 students)
IR – carbonyl or C=O
41.4% (7 students) 2 equivalent or 2 unique or 2 identical or proper # of equivalent
sets of hydrogens
35.3% (6 students) H-NMR
29.4% (5 students) Ratio of:
- 6:4
- one set of two hydrogens and one set of three hydrogens
- 4:6 ratio
Group of 6 with 4 vicinals and group of 4 with 6 vicinals
2 sets of hydrogen – one with 3 hydrogens (4 vicinal) and one with
2 hydrogens (6 vicinal)
15
Results from Quiz #4 – Spectroscopy (2)
29.4% (5 students) Process of elimination
- C-13 NMR – one set of carbons with no hydrogens – eliminate C
- eliminate D and A – no carbonyl
- IR – no evidence of OH – eliminate A
- IR shows C=O. Can’t be D.
- Peak of alcohol not there – cannot be A
- C has more than 3 unique sets of hydrogens and would have CH3, CH2,
and CH peak – not equivalent to C-13 NMR
23.5% (4 students) IR – no evidence of OH
23.5% (4 students) 1 CH3, 1 CH2, and possibly mentioned 1 C (no protons
attached)
11.8% (2 students) Mass spec
- parent peak of 57 – corresponds to CH3CH2C=O – student was correct
- molecular weight of molecule is 86 g/mole which can be seen on the
mass spec – student did NOT choose the correct structure
Miscellaneous
- C 13 – 195-220 peak is for ketones
- 3 peaks on C-NMR – 3 sets of equivalent carbons
- C-NMR backs up H-NMR
16
Results from Quiz #4 - Spectroscopy
11.8% (2 students) Incorrect responses
- It cannot be A because the peak for an alcohol is not there. The
compound cannot be B because the hydrogen sets are symmetric
and therefore there wouldn’t be two sets of 2 and 4 peaks showing
up. The compound D cannot be chosen because of the same reason
for B. Even if it were to have two sets it would create 2 triplets.
The answer has to be C because the hydrogen on the #1 carbon
creates the doublet and the set of the hydrogens on carbons 2-5
create the triplet.
- I looked at the NMR and saw the peak at 4, meaning a benzene ring.
Also, one C-O bond can be seen on the IR spectra. Also, the
molecular weight of the molecule is 86g/mol, which can be
seen on the mass spec.
17