Quizzes and Results from an Organic Chemistry Molecular Modeling Study American Chemical Society New York City September 11, 2003 Jim Hermanson

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Quizzes and Results from an Organic Chemistry
Molecular Modeling StudyAmerican Chemical
SocietyNew York CitySeptember 11, 2003Jim
Hermanson Julie B. EalyPenn State
UniversityBerks-Lehigh Valley
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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.
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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
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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 electronsare 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).
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Quiz 2
A B
C D
Black-carbon Red-oxygen Green-hydrogen
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.
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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 ADBC ACBD ABDC DBCA ACDB
of students 14 1 1 2 1
73.7 5.26 5.26 10.5 5.26
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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 36.8 Incorrect
Answer CBDA DBCA ACBD CABC BDCA ACBA CDBA
of students 12 1 1 1 1 2 1
63.2 5.26 5.26 5.26 10.5 5.26 5.26
Its 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.
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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
statingelectronegativity 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)
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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

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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.
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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.
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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.
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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.
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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.
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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
Structure A B C D
of students 0 15 1 1
of students 0 88.2 5.88 5.88
Question 2. Explain how your choice was made.
(The percentages do not total 100. A students
responses were included in more than one
category.) 47.1 (8 students) IR carbonyl or
CO   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 - 64 -
one set of two hydrogens and one set of three
hydrogens - 46 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)
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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 CO.
Cant 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 CH3CH2CO
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
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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 wouldnt 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.