Ian R. Gould
the exam cover sheets look kind of like this
PRINTED
FIRST NAME
PRINTED
LAST NAME
ASU ID or
Posting ID
THIS IS A CHM 233 PRACTICE EXAM
Person on your LEFT (or Aisle)
Person on your RIGHT (or Aisle)
1__________/14 ........
MIDTERM #2
3__________/6 ........
PRACTICE TEST #1
4__________/22 ........
• PRINT YOUR NAME ON EACH PAGE!
2__________/27 ........
• READ THE DIRECTIONS CAREFULLY!
• USE BLANK PAGES AS SCRATCH PAPER
work on blank pages will not be graded...
5__________/14 ........
•WRITE CLEARLY!
6__________/44 ........
• MOLECULAR MODELS ARE ALLOWED
7__________/24 ........
• DO NOT USE RED INK
8__________/24 ........
• DON'T CHEAT, USE COMMON SENSE!
Total (incl Extra)________/175+5
Extra Credit_____/5
H
He
Li Be
B
N
O
F
Ne
Na Mg
Al Si P
S
Cl
Ar
Ga Ge As Se Br
K
Ca
Sc Ti V
Cr Mn Fe Co Ni Cu Zn
Rb Sr
Y
Zr Nb Mo Tc Ru Rh Pd Ag Cd
Cs Ba
Lu Hf Ta W
small range
range of values
broad peak
Re Os Ir Pt Au Hg
O H
C N
N H
C O
C
~1.0
Kr
H/Me
In Sn Sb Te I
Xe
Me/Me
Tl Pb Bi Po At
Rn
Me/Et
H
C
N H
C
N
1600–1660
N
11
220 O
10
200
R C OH
1735
CH
H
~10
~8
H
1600
O
H
O
C CH3
–H2C NR2
7
140
6
120
5
100
R2C CR2
Aromatic
C CH
4
80
3
60
RC
CR
Alkyl
3Y > 2Y > 1Y
2
40
–OCH2–
R C N
H
~15
C C
1500
C CH2
8
160
~2
H
NR2
–OCH2–
NMR Correlation Charts
H
H
C
2000
~2
C C
O
Aromatic Ar H
mainly 8 - 6.5
O
C
~7
H
C C
1650
2500
9
180
H H
H
–H2C X
(δ, ppm)
Approximate Coupling
Constants, J (Hz), for
1H NMR Spectra
OR
1710
3000
O
C H
~2.7
1680
C
2200
amine R NH2 variable and condition
alcohol R OH dependent, ca. 2 - 6 δ
O
R C OH
t-Bu/Me
C C
C
O
C O H
3500
~2.9
O
broad ~3000
(cm-1)
~1.1
H
C
2850–2960
broad ~3300
~0.95
i-Pr/Me
C
C
H
broad with spikes ~3300
O H
Et/Me
~2.6
C
2200
C
~1.4
O
2720–2820
2 peaks
3000–
3100
~0.9
Infrared Correlation Chart
H
C
3300
Me/Me
usually
strong
H
Gauche
Eclipsing
H/H
O
C H
Interaction Energies, kcal/mol
1
20
0
0
Alkyl 3Y > 2Y > 1Y
C X
C NR2
CHM 233 Practice Exam : Mid #1 : Practice Exam #1
NAME
Question 1: Draw Newman projections and 3-D (sawhorse) structures for the 3 staggered
conformations for rotation around the central C-C bond of 2,3-dimethylbutane. Identify the
lowest and highest energy of these three conformations, and give a BRIEF explanation
for your choice.
H
CH3
CH3
H3C
H
gauche
CH3
gauche
lowest energy
C C
(2
gauche
interactions)
H
C
H3C
CH3
3
H
C
H
H
3
H
gauche
H3C
C
H3C
H3C
CH3
CH3
gauche
CH3
gauche
H
H
H
CH3
H3C
CH3
gauche
CH3
gauche
CH3
H
C
H
H
H3C
H
equal and higher in energy
(3 gauche interactions)
CH3
C C
H3C
CH3
H3C
gauche
there will always be different but still correct ways of drawing these Newmans and 3-d
sawhorse structures depending upon which direction you choose to "look" at the
molecule, I can't include all of them here, you need to decide if yours match mine, a
model always helps!
Question 2: Give a IUPAC name for the following structure.
Br
Br
"up"
"down"
H
H
=
Br
"up"
cis-1,2-dibromocyclopentane
Br
"up"
Question 3: Give TWO MINOR resonance contributors (include curved arrow pushing and
resonance arrows/brackets) that explains why electrons A are lower in energy than
electrons B in the following structure, give a BRIEF explanation that relates electron energy
to resonance
A
X
H2N
O
B
NH2
NH2
H2N
O
NH2
H2N
O
the electrons A are resonance stabilized, the electrons B are not, resonance
delocalization lowers the energy of the electrons by allowing them to "see" more nuclei in
a partial bonding sense
NAME
CHM 233 Practice Exam : Mid #1 : Practice Exam #1
Question 4: For A, B and C, draw the lowest energy chair conformations (this will always be
the one that has the t-butyl group equitorial), and then rank the three lowest energy chairs
(one A, one B, one C) in order of INCREASING energy, give a BRIEF explanation for your
ranking.
Me
A
t-Bu
Me
t-Bu
B
Me Me
t-Bu
t-Bu
Me
C
B
Me
t-Bu
lowest
<
C
<
A
highest
t-Bu
All 3 must have the t-butyl equitorial. In B both methyls are also equitorial which is the lowest
energy conformation which avoids the gauche interactions associated with the axial position, C
has 1 methyl axial and A has both methyls axial, thus A is highest in energy
Question 5: For the infrared absorption bands that correspond to the stretching vibrations
of the double bonds indicated as A, B and C, rank in order of INCREASING intensity
(absorption strength, not absorption frequency), give a BRIEF explanation that inclides teh
term "electric field vector of the electromagnetic radiation".
A
O
lowest
CH2
B
B
<
C
<
A
C
S
highest
absorption intensity increases with increasing bond dipole moment, since it is the bond
dipole that interacts with the leectric field vector of the infrared electromagnetic radiation,
bond dipole moment increases with increasing electronegativity difference between the
atoms in the bond, thus O is more electronegative than S which is more electronegative
than C
CHM 233 Practice Exam : Mid #1 : Practice Exam #1
NAME
Question 6 Assign the BOTH IR spectra to ONE of the FOUR provided structures A - D. Two
of the structures do not have a provided spectra. On each spectrum, identify the peaks that
are associated with a specific functional group or type of C-H bond by drawing the
functional group or bond and drawing an arrow from the specific bond in the
functional group that vibrates to the absorption peak, as appropriate.
O
C
OCH3
O
O H3CH2C
H3CO
OCH3
NH2
H3C
B
A
D
C
1909
1063
NH2
1461
3401
N
3029 2894
H 3330
2929
CH2CH3
1127
C
H
1272
2963
H
C(sp2)
H
C
sp3
1619
827
1516
3008
29632902
2003
H
C
sp3
H
C(sp2)
O
1367
R
1510
1682
1035
1170
1604
1271
832
CHM 233 Practice Exam : Mid #1 : Practice Exam #1
NAME
Question 7: Provided are spectra for a compound with molecular formula C5H12O,
determine the structure by answering the questions below
a) Give the degrees of unsaturation
0 degrees of unsaturation
________________
b) On the infrared spectrum, indicate the peaks that identify the functional groups in the
molecule (including C(sp3)-H). Indicate BOTH the functional group, and where appropriate,
the specific BOND in the functional that corresponds to the peak.
on a test the
individual peak
positions will be
provided
H C
R
sp3
O
H
IMPORTANT it is INSUFFICIENT to just label these peaks as "sp3" since this
implies that you do not understand that signals represent the vibrations of
bonds between HYDROGEN ATOMS and sp3 hybridized carbons
c) draw the structure and clearly indicate which hydrogens correspond to which signals in the
proton nmr spectrum ONLY
it would NOT be necessary for YOU to assign the 13C spectrum
3H b
doublet
e
f
b
d
1H a
singlet
c
protons d and e
overlap and can't be
distinguised in this
spectrum
d,e
4H
multiplet
OH a
H3C
f
CH2
CH
CH2 c CH3
e
b
d
"real" nmr spectra, for instance those you may
see in the lab, often have difficulties such as
overlapping peaks as in this case
1H c
sextet
3H f
triplet
NAME
CHM 233 Midterm #2 : Practice Exam #2
THIS IS THE START OF PRACTICE EXAM #2
Question 1:
a) Draw a Newman projection of the 3 staggered conformations of 2,3-dimethylbutane for
rotation around the C2-C3 bond, and give their relative energies (not absolute energies, you
do not need to do an energy calculation here).
2
4
3
1
Me
H
H
Me
H
Me
H
Me
Me
Me
Me
H
Me
Me
Me
H
Me
Me
lowest energy
(2 gauche interactions)
equal and higher in energy
(3 gauche interactions)
b) Using the Wedged/Dashed formalism, draw 3-D (sawhorse) structures for the 3
equivalent staggered conformations of 2,3-dimethylbutane, and give their relative (not
absolute) energies.
Me
Me
H
Me
H
H
CH3
CH3
H
H
C
C
C
C
= H C
H3C
3
CH3
Me
H3C
CH3 H3C
CH3
CH3
H3C C C
=
H
H3C
H
H
3 gauche
equal and higher in energy
(3 gauche interactions)
Me
Me
lowest energy
(2 gauche interactions)
H
H
Me
Me
2 gauche
Question 2: Determine the energy difference between the 2 chair conformations of trans-1,2dimethylcyclohexane.
Me
2 x Me/Me gauche
= 1.8 kcal/mol
AND
2 x Me/Me gauche
= 1.8 kcal/mol
Me
Me gauche
Me
H
H
H
H
H
H
Me
Me
gauche
1 x Me/Me gauche
= 0.9 kcal/mol
total = 3.6 kcal/mol
ΔE = 2.7 kcal/mol
EXTRA CREDIT: Which of these techniques forms the basis for the device that is used to detect
traces of explosives and/or narcotics at airport security checkpoints?
mass
spectrometry
infrared
spectroscopy
proton nmr
spectroscopy
carbon nmr
spectroscopy
CHM 233 Midterm #2 : Practice Exam #2
NAME
Question 3: Give IUPAC names for the following structures.
Me
3
Substituents numbered alphabetically
because (and ONLY because)
everything else is equal in this case.
2
1 Et
cis-1-ethyl-3-methylcyclohexane
1
2
3
45
6
8
7
9
10
5-butyl-4-isopropyl-2-methyldecane
Question 2: Rank the three indicated carbon-hydrogen bonds, C-Ha, C-Hb and C-Hc, in order of
INCREASING bond dissociation energy. Give a BRIEF explanation that includes drawings of
resonance contributors as appropriate.
Hc
Hb
Hc
Ha
<
<
Hb
Ha
1°
smallest BDE
homolytic cleavage gives a resonance
stabilized radical in EACH case
2°
Hc
H
H
largest BDE
for Hc these are formally 1° and 2° in the
resonance contributors
for Hb these are formally 2° and 2°
Hb
2°
H
H
3°
Hc
for Ha these are formally 3° and 3°
2°
3°
radical stability increases with increasing
substitution of the radical center lowers
electron energy), the radical from Ha cleavage
is the most stable, thus C-Ha has the smallest
BDE etc.
CHM 233 Midterm #2 : Practice Exam #2
NAME
Question 6 Assign the BOTH IR spectra to ONE of the FOUR provided structures A - D. Two
of the structures do not have a provided spectra. On each spectrum, identify the peaks that
are associated with a specific functional group or type of C-H bond by drawing the
functional group or bond and drawing an arrow from the specific bond in the
functional group that vibrates to the absorption peak, as appropriate.
O
O
O
O
H
A
H
B
3309
O
C
D
O
675
H
B
1127
2705
903
952
O
H
2932
2809
H
sp3
C
1461
1708
2608
O
829
D
1299
1078
1195
1407
2867
H sp3
C
O
R
2942
1707
CHM 233 Midterm #2 : Practice Exam #2
NAME
Question 7: Provided are spectra for a compound with molecular formula C9H12,
determine the structure by answering the questions below
a) Give the degrees of unsaturation
4 degrees of unsaturation
________________
b) On the infrared spectrum, indicate the peaks that identify the functional groups in the molecule
(including C(sp3)-H). Indicate BOTH the functional group, and where appropriate, the specific
BOND in the functional that corresponds to the peak.
C H
H C
sp2
on a test the
individual peak
positions will be
provided
sp3
IMPORTANT it is INSUFFICIENT to just label these peaks, for example, as
"sp3" since this implies that you do not understand that signals represent the
vibrations of bonds between HYDROGEN ATOMS and sp3 hybridized carbons
c) draw the structure and clearly indicate which hydrogens correspond to which signals in the proton
nmr spectrum ONLY
a
6H
3 peaks here
solvent
X
H
H
c
H
H
H
a
CH3
CHb
CH3
a
the i-Pr group is only weakly donating,
and so in this case the 5 hydrogens on
the benzene ring have similar chemical
shifts (they are often more spread out
with strong -D or -W groups), they
overlap extensively and simply
contribute to one large 5H signal
c
5H
b
1H
CHM 233 Practice Exam : Mid #2 : Practice Exam #3
NAME
THIS IS THE START OF PRACTICE EXAM #3
Question 1: Give the IUPAC name for the following structure.
7 6
8
1
2 3 45
5-ethyl-2,6-dimethyloctane
Question 2: Draw Newman projections of BOTH the most and the least stable conformations of
2-methylbutane, along the C2-C3 bond, AND calculate the energy difference between them.
Give a 3-D (sawhorse) structures for each structure.
H
H
Me
Me
C C Me
Me
H
CH3
H
H
H
CH3
Me
C
H H
C
H
Me
ΔE = 5.0 - 0.9 = 4.1 kcal/mol
CH3
CH3
CH3
most stable
1 Me/Me gauche = 0.9
H
H
H
CH3
least stable
1 Me/Me eclipse interactions +
1 Me/H eclipse interaction +
1 H/H eclipse intraction =
(1 x 2.6) + 1.4 + 1.0 = 5.0 kcal/mol
Question 3: Which nuclei "see" the larger effective magnetic field, those with large chemical shift or
those with small chemical shift, and give a brief explanation.
The effective field is determined by the magnitude of the applied external field, and the
internal field that OPPOSES the external field that is generated by the electrons around the
nuclei. The opposing field induced by the electrons SHIELDS the nuclei, reducing the effective
field. Reduced shielding due to electronegativity or unsaturation, i.e. DESHIELDING,
increases the effective magnetic field, which corresponds to a larger chemical shift BY
DEFINITION.
CHM 233 Practice Exam : Mid #1 : Practice Exam #3
NAME
Question 4: Match the IR spectra to the 4 provided structures. Om each spectrum indicate
BOTH the identifiable functional group absorptions, and where appropriate, the specific
BOND in the functional group that corresponds to the absorption peak(s).
O
CH3CH2 C CH2CH3
A
CH3 O
H3C C C
CH3 H
B
B
H2C CH-CH2CH2CH2-OH
C
R
H
C
C
D
O
H
O
sp3
H
R (aldehyde)
R O
H
H
C
sp3
H
C(sp2)
C C
D
H
C C H
sp
sp3
C C H
C
A
H
sp3
C
O
R
HC C-CH2CH2CH2CH3
R (ketone)
NAME
CHM 233 Practice Exam : Mid #1 : Practice Exam #3
Question 5: For each of the alkenes A and B, draw one MINOR resonance contributor
(include curved arrows and resonance arrows/brackets) and on that basis decide which
would you expect to have the lower frequency for the C=C vibration in infrared spectroscopy
and give a brief explanation.
OH
NH2
OH
A
NH2
B
The more the minor resonance contributor contributes the more single bond character the C=C
bond has, the weaker the C=C bond, the lower the vibration frequency
in A the formal positive charge is on the more electronegative oxygen, in B it is on the less
electronegative nitrogen, a positive charge is more stable on the less electronegative element,
the minor contributor is more important in B, B would have the LOWER vibration frequency
Question 5. For the following cations, draw as many additional resonance contributors as
are reasonable (include curved arrows and resonance arrows/brackets), indicate the
hybridization of ALL of the non-hydrogen atoms, indicate the major contributor as appropriate
and briefly justify your choice and draw an "actual" or resonance hybrid structure
for A: indicate partial charges using exact fractional charges, i.e. 1/2+, 1/3+, 1/4+ etc,
do not simply use the δ notation
for B: you can use the δ notation to indicate the partial charges
δ
A
δ
EQUAL
"actual"
ALL carbons are sp2 hybridized
the 2 contribute equally to the resonance mixture, they have the same number of bonds, same
charges on same atoms etc.
••
••
HO
HO
HO
••
••
••
••
B HO
••
major
ALL carbons and the oxygen are sp2 hybridized, except the 2 that are circled, they are sp3
δ
••
this major contributor has the lowest formal
electron energy because it has the most formal
bonds
HO
δ
δ
δ
"actual"
CHM 233 Practice Exam : Mid #1 : Practice Exam #3
NAME
Question 8: Identify the compound with the following spectra and molecular formula C4H8O2.
On the infrared spectrum, indicate the peaks that identify the functional groups in the molecule
(including C(sp3)-H). Indicate BOTH the functional group, and where appropriate, the
specific BOND in the functional group that corresponds to the peak. Give the degrees of
unsaturation.
C4H8O2: (4 * 2) + 2 = 10 H atoms max
8 H atoms actually, thus degees = (10 - 8)/2 = 1 degree of unsaturation
in an exam
question the exact
frequencies of the
peaks would be
provided form you
O
CO H
H-C(sp3)
O
broad
CO H
Determine the structure of the molecule and assign each of the signals in the proton nmr
spectrum (only) to the hydrogen atoms in your structure
O
CO H
D
A
1H
3H
singlet
all other carbons are NOT
magnetically equivalent
you would not need to
assign these signals
triplet
B
2H
sextet
O
H3C
A
CH2
B
CH2
C
only possible structure AND
the proton nmr spectrum
predicted for this matches
the provided spectrum
C
C
OH
D
2H
triplet
NAME
CHM 233 Practice Exam : Midterm #2 : Practice Exam #4
Start of Practice Exam #4
Question 2: Give the IUPAC name for the following structures.
trans-1-ethyl-3-isopropylcyclobutane
1' 2' 3'
2
1
3
4
5
6
7
8
9
4-(1,2-dimethylpropyl)-2,2,3-trimethylnonane
Question 3: Draw Newman projections of BOTH the most and the least stable conformations of
2,2-dimethylbutane, along the C2-C3 bond AND calculate the energy difference between them
and give 3-D (sawhorse) structures for each.
H
H
C
C
Me
H
H3C
Me
Me
Me
Me
CH3
H
Me
C
most stable
C
Me
H H Me
least stable
CH3
CH3
ΔE = 5.4 - 1.8 = 3.6 kcal/mol
CH3
CH3
2 Me/Me gauche interactions =
2 x 0.9 = 1.8 kcal/mol
H3C
H
H
CH3
1 Me/Me eclipse interactions +
2 Me/H eclipse interaction =
(1 x 2.6) + (2 x 1.4) = 5.4 kcal/mol
CHM 233 Practice Exam : Midterm #2 : Practice Exam #4
NAME
Question 4: Assign EACH IR spectra to ONE of the FOUR provided structures A - D. One of
the structures does not have a provided spectrum. On each spectrum, identify the peaks
that are associated with a specific functional group or type of C-H bond by drawing the
functional group or bond and drawing an arrow from the specific bond in the
functional group that vibrates to the absorption peak, as appropriate.
O
O
CH3CH2 C OCH3
O
OH
A
H
B
3321
D
C
3198
3065
C
3031
C H
C
2799
sp2
2702
O
H
O
R
1231
1421
1398
1598
H
1201
1699
conjugated
814
1981
2921
3023
C
3019
C
2948
C H
H
sp3
1599
1469
D
1091
3010
sp2
1498
731
698
3205
2940
A
H
1411
C
sp3
2983
O
R
OR
1735
1391
1051
1229
CHM 233 Practice Exam : Midterm #2 : Practice Exam #4
NAME
Question 5: Why is the energy associated with having one substituent axial approximated as
twice the energy of a substituent/methyl gauche interaction?
The substituent has a 60 degree dihedral angle, and thus a gauche interaction, with two of the
other carbons in the rest of the cyclohexane right. Although these two carbons in the ring are not
methyl groups, it is assumed that the gauche itneraction is similar to a methyl group.
Question 6: For each of the following structures, draw the 2 chair conformations and determine
the energy difference between them, clearly indicate ALL of the energy contributions that you take
into account when determining the energy difference
a) cis-1-ethyl-4-methylcyclohexane
Et
Me
Me
Et
2 x Et/Me gauche
= 1.9 kcal/mol
2 x Me/Me gauche
= 1.8 kcal/mol
Et
Et
Me
Me
b)
Me
i-Pr
gauche
i-Pr
i-Pr
ΔE = 0.1 kcal/mol
Et
2 x Me/Me gauche = 1.8
kcal/mol
2 x Et/Me gauche = 1.9
kcal/mol
TOTAL = 3.7 kcal/mol
2 x i-Pr/Me gauche = 2.2
kcal/mol
1 x Me/Et gauche = 0.95
TOTAL = 3.15 kcal/mol
ΔE = 3.7 - 3.15 = 0.55 kcal/mol
H
H
H
i-Pr
H
Me
Me
Et
gauche
CHM 233 Practice Exam : Midterm #2 : Practice Exam #4
NAME
Question 7: Provided are spectra for a compound with molecular formula C6H12O2,
determine the structure by answering the questions below
degree of unsaturation
a) Give the degrees of unsaturation 1________________
b) On the infrared spectrum, indicate the peaks that identify the functional groups in the
molecule (including C(sp3)-H). Indicate BOTH the functional group, and where
appropriate, the specific BOND in the functional that corresponds to the peak.
C(sp3)-H
O
C=O
6H
d
a
3H
CH3
O
H3C
a
CH2
b
O
CH
c
b
d
2H
c
CH3
1H
multiplet
NAME
CHM 233 Practice Exam : Midterm #2 : Practice Exam #5
Start of Practice Exam #5
Question 1: Give a line-angle structure and the IUPAC name for the condensed formula
CH3CH2C(CH3)2CH(CH2CH3)CH2C(CH3)2CH2CH3
1
4
2
5
3
7
6
8
4-ethyl-3,3,6,6-tetramethyloctane
Question 2: Rank in order of increasing bond dissociation energy of the indicated C-H bond.
Give a BRIEF explanation, include drawings oif resonance contributors as appropriate.
H
H
H
A
B
<
B
C
C
<
A
In A, the bond is "made" from 1s A.O. on hydrogen and sp2 A.O. on carbon,
thus strongest
In C the bond is "made" from 1s A.O. on hydrogen and sp3 A.O. on carbon,
thus weaker
In B, the bond is "made" from 1s A.O. on hydrogen and sp3 A.O. on carbon,
and the radical is resonance stabilized, thus weakest
H
Question 3: Why do atoms in molecules have hybridized atomic orbitals?
The atoms respond to the fact that they are surrounded by other atoms in a molecule (really,
the positive and negative charges) and their orbitals correspondingly respond in order to, for
example, make bonds that are either similar to or different from other bonds, with specific
angles, i.e. bonds that the atoms could not make using its unhybridized atomic orbitals.
CHM 233 Practice Exam : Midterm #2 : Practice Exam #5
NAME
Question 4: Which cation A or B has the more reactive non-bonding electrons? Give a BRIEF
explanation using resonance arguments, draw all relevant resonance contributors, your
explanation must mention electron energy.
NH2
NH2
NH2
NH2
NH2
NH2
A
no resonance
contributors can be
drawn that involve
these non-bonding
electrons
NH2
B
delocalization means stability, the electrons "see" more nuclei, no resonance contributors
can be drawn for cation B that involve the non-bonding electrons on the nitrogen, these
electrons are not delocalized, they are not stabilized by resonance, they are higher energy,
they are more reactive
Question 5. For the following structure, draw MINOR resonance contributors (include curved
arrows and resonance arrows/brackets) and rank the indicated carbon atoms A, B and C in
order of INCREASING chemcial shift in a carbon nmr spectrum. Give a brief explanation that
includes discussion of the factors that control deshielding, as appropriate
O
O
O
A
B
C
B
smallest δ
<
C
<
A
largest δ
the minor resonance contributor reveals a partial negative charge on
carbon B, which will increase electron density at B which will reduce the
strong deshielding caused by the benzene ring, B is least deshielded
and will have the smallest chemical shift
Carbon A is directly attached to the electronegative oxygen, which has a
partial positive charge in the minor resonance contributor, the oxygen
decrease electron density at A, further deshielding, A has teh largest
chemical shift
C is intermediate
CHM 233 Practice Exam : Midterm #2 : Practice Exam #5
NAME
Question 6. Convert the following Newman projection into a line-angle structure, draw both
chaior conformations and indicate the lowset energy chair, give a BRIEF explanation
H
H
Et
H
H
H
H
Et
=
1
Et
2
3
Me
Me
Me
lower energy
Et
Me
the lower energy chair has the smaller -Me substituent axial, avoiding the higher energy
gauche interactions of the larger Et group axial in the other chair
Question 7. For the following anion, draw as many additional resonance contributors as are
reasonable (include curved arrows and resonance arrows/brackets), indicate the
hybridization of ALL of the non-hydrogen atoms, indicate the major contributor as
appropriate and briefly justify your choice and draw an "actual" or resonance hybrid
structure, you can use the δ notation to indicate the partial charges
••
••
••
O
Oδ
O
••
••
••
••
O
••
δ
major
δ
actual
••
the major contributor has the formal negative charge on most electronegative atom
oxygen, the major has the lowest formal energy for the electrons
CHM 233 Practice Exam : Midterm #2 : Practice Exam #5
NAME
Question 7: Provided are spectra for a compound with molecular formulaC5H10O2,
determine the structure by answering the questions below
degree of unsaturation
a) Give the degrees of unsaturation 1________________
b) On the infrared spectrum, indicate the peaks that identify the functional groups in the
molecule (including C(sp3)-H). Indicate BOTH the functional group, and where
appropriate, the specific BOND in the functional that corresponds to the peak.
2096
3402
813
1439
2989
1306
H
H
2996
C
1352
sp3
1719
O
C
O
1009
1094
1186
cm-1
c) draw the structure and clearly indicate which hydrogens correspond to which
signals in the proton nmr spectrum
3H
O
CH3
2H
C
CH2
O
CH2
CH3
2H
3H