CHEM 40 University of California Chemistry Exam Practice

1. 1H NMR Spectroscopy (18 points).A. Label the equivalent sets of hydrogens in the molecules below and state clearly how many different
resonances you expect in the 1H NMR spectrum (4 pts each).
f
e
g
H
H
H
dH
CH3O
a
H
h
H
e
Br
Hd
OCH3
Br
H cH
a
a
H
HH
f
6 resonances
Ha
b
H
H
a
aH
cH
H
d
Br
a
c
H
b
OH
a
8 resonances
H
b
H H HH H H H
g
H H h
b
d
f
CH3
Hb
Ha
Hc
Hd
Br
aH
4 resonances
Hb
Ha
2 resonances
B. Predict the 1H NMR spectral appearance of the molecule below, including the number of resonances,
their splitting patterns (if any) and the approximate chemical shifts of the resonances (6 pts).
e
CH3 d
H
H
H3C Si O
O
Hf
CH3
H
O
b
Ha
a – doublet
c
6 resonances
b – doublet of doublets or quartet or 4 lines
c – singlet
d – doublet
e – doublet
f – doublet
2. 13C NMR Spectroscopy (18 points).
A. Label the equivalent sets of carbons in the molecules below and state clearly how many different
resonances you expect in the 13C NMR spectrum (4 pts each).
a
e
f
b
c
H3CO c
OCH3
d
e
Br
b
Br
e
e
5 resonances
a
a
b
b
c
c
d d
Br
OH
b
6 resonances
a
a
c
d
a
b
a
Br
a
4 resonances
b
a
2 resonances
A. Predict the 13C NMR spectral appearance of the molecule below, including the number of resonances,
and their splitting patterns in the off-resonance 1H decoupled spectrum (6 pts).
O
d
e
f
c
Cl
b
a
g
7 resonances
a – triplet in off resonance 1H decoupled spectrum
b – singlet
c – singlet
d – singlet
e – singlet
f – triplet
g – quartet
3. Alkenes (24 points). Show 8 transformation of the alkene shown below. Include stereochemistry as
appropriate. Where new stereochemistry is formed, indicate whether the reaction involves syn or anti
addition. If enantiomers are formed, only one enantiomer may be shown.
anti addition
Br
X
H
H
Br
or
OH
Br
Br
X2
HX
Br
H
H
Br
X2 / H2O
or
OH
H + / H 2O
H2 / metal catalyst
OH
anti addition
1) BH3
2) H2O2 / -OH
OsO4
RCO3H
H
OH
OH
or
HO
HO
O
H
H
H
H
syn addition
OH
syn addition
or
O
syn addition
OH
or
H
4. Structure Elucidation (20 points). From the spectral data on this and the next page, deduce the structure
of the compound. The molecular formula is C8H13NO2. Label each resonance in the 1H and 13C NMR
spectra.
This is an expansion of a part of the first spectrum.
Compound is:
c
O
b a
b a N
O
b
H
c
N H
a
b
O
O
13C NMR spectrum
1H NMR spectrum
a – δ 184 ppm
b – δ 48 ppm
c – δ 22 ppm
a – δ 7.5 ppm
b – δ 1.25 ppm
5. Chemical Reactions (20 points). Draw the organic products of the following reactions, being mindful of
stereochemistry. In reactions that form enantiomers, draw one of the two enantiomers.
HCl
A.
Cl
O
B.
K+
Br
major product only
C.
O
O
O
O
CH3CO3H
excess reagent
two diastereomeric products
D.
Br2
Br
OsO4
E.
Br
H 2S
HO
HO
major product only
HH
H2
F.
Pd
H
OH
1) BH3
G.
2) H2O2 /
OH
OH
Cl
H
Cl2 / H2O
H.
Br
Br2
H
I.
Br
H
H
H
Br2
J.
OH
H
or
O
H
O
Br
H
Br
6. Reaction Mechanisms (15 points). Provide reasonable mechanisms for the three reactions below. Each
part is worth the same number of points.
N3
Br2
A.
Br
NaN3
Br
Br
N3
Br
Br
N3
I
ICl
B.
Cl
I
I Cl
I
Cl
– Cl –
Cl –
I2
C.
HO
O
+
I
HI
I
I
I
HO
-I-
HO
O
H
I
-H+
O
I
7. Synthesis (15 points). Provide reasonable methods for the synthesis conversions below. More than one
step may be involved. All parts of this problem are worth the same number of points
1) BH3
A.
OH
2) H2O2 / OH
OH
B.
OH
OH
OsO4 / H2S
H2SO4 / heat
C.
Br2
excess strong base
Br
Br
8. Challenge Question (20 points maximum). Do one of the two problems below. Clearly indicate which
part you want graded by circling the letter corresponding to the problem.
A. From the spectral data below, deduce the structure of the compound. The compounds formula is
C6H12O2. Label each resonance in the 1H and 13C NMR spectra. Note: the broad peak at d 3.8 in
the 1H NMR spectrum is due to an OH group. Part A is worth 20 points.
13C NMR:
1H NMR:
a – δ 31 ppm
b – δ 211 ppm
c – δ 43 ppm
d – δ 29 ppm
a – δ 2.2 ppm
c – δ 2.61 ppm
d – δ 1.2 ppm
f – δ 3.8 ppm
d
c
e
HO
f
d
b
O
a
B. Give a reasonable mechanism for the transformation below. Part B is worth 10 points.
H + / H 2O
H
O
O
H
H
H+
H
O
– H+
H
H
O
O
– H+
O
1. Alkene Chemistry (10 points) Using 1-methylcyclohexene as the starting material, draw 5 reactions
that give different products containing at least one bromine atom. Clearly indicate stereochemistry, if
any.
students choice – must follow reactivity rules
2. Structure Elucidation (20 points). From the spectral data on this page, deduce the structure of the
compound. The molecular formula of the compound is C8H7ClO. Label each resonance in the 1H and 13C
NMR spectra.
O
O
or
Cl
Cl
13C NMR:
δ 197 – carbonyl
δ 140 and 135 – aromatic substituted carbons
δ 130 and 129 – aromatic unsubstituted carbons
δ 27 – CH3
1H NMR:
δ 2.6 ppm – CH3
δ 7.8 – 2H ortho to carbonyl
δ 7.3 – 2H meta to carbonyl
3. Alkyne Chemistry (16 points). Draw 8 reactions of 1-butyne. Only two of them may result
in the same product. Clearly indicate stereochemistry, if any.
CH3CH2 C C H
1- butyne
CH3CH2 C C Na+
NaNH2
2 H2
metal catalyst
H2 Pd-BaSO4
quinoline
Na or Li
NH3
CH3CH2 C C H
1- butyne
2 X2
HX
X
X2
X
X
X
X
X
X
students choice must follow the rules of reactivity
4. Aromaticity (10 points). Label each of the compounds below as either aromatic, anti-aromatic or
neither. Assume all of these molecules are planar.
anti-aromatic
aromatic
neither
neither
aromatic
5. Chemical Reactions (30 points). Draw all of the organic products of the following reactions, being
mindful of stereochemistry. In reactions that form two enantiomers, draw one of the two enantiomers.
Cl
A.
Cl
excess HCl
Cl
1) NaNH2
B.
2)
Br
H
1) BH3
C.
2) H2O2 / OH
OH
O
E.
heat
+
D.
Cl
Cl
O
HNO3
H2SO4
Cl
Cl
NO2
O
F.
H
1) NBS / heat
H O
O
2)
K+ O
O
O
O
3)
heat
O
O
Cl
G.
AlCl3
1 equivalent
HBr
H
H.
Br
1) 1 equivalent Br2
I.
2) 2 equivalents of strong base
Br
Br
Br2
J.
FeBr3
two monobromo isomers
6. Reaction Mechanisms (20 points maximum). Provide reasonable mechanisms for two of the three
reactions below. Part A is worth 5 points, part B is worth 8 points and part C is worth 12 points. Clearly
indicate which two parts you want graded by circling the letter corresponding to the problem. To get the
maximum number of points on this problem, you must do parts B and C.
O
O
OH
H+
A.
+
O
O
O
H+
O H
O H
O
O
O
O
O
O
O
electrophile in an EAS process
O
OH
OH
O
B.
O
H O
OH
– H+
O
O
OH
H+
O
H
O
O
H+
H
O
H
OH
OH
– H+
C.
OH
O
Br2
Br
OH
H
O
OH
– Br –
Br
Br
Br
Br
OH
Br
H
O
Br
– H+
O
Br
7. Synthesis (20 points maximum). Synthesis (20 points maximum). Provide reasonable synthesis
pathways for the conversions below. You may use any organic and inorganic reagents. The carbon atoms of
the starting material must be incorporated into the target molecule. Part A is worth 5 points, part B is worth
8 points and part C is worth 12 points. Clearly indicate which two parts you want graded by circling the
letter corresponding to the problem. To get the maximum number of points on this problem, you must do
parts B and C.
X
X
A.
AlX3
B.
H
H
H
H
H2
Pd BaSO4
quinoline
1) NaNH2
2) CH3CH2Br
1) NaNH2
2) CH3CH2CH2Br
H
Br
COOH
Br
COOH
C.
heat
2 Br2
COOH
COOH
Br
Br
Br
Br
2 K+ OtBu
Br
or other
strong base
Br
8. Challenge Question (24 points). Do one of the two problems below. Clearly indicate which part you
want graded by circling the letter corresponding to the problem. Each part is worth 24 points.
A. The 1H NMR spectrum of monosubstituted benzene rings exhibits 3 resonances in a typical pattern
consisting of a doublet (2H), a triplet (2H) and another triplet (1H). The 13C NMR spectrum of a
monosubstituted benzene ring shows 4 resonances. Explain both of these observations.
G
B. Cyclopentadiene is not stable on storage due to its propensity to react with itself to form a dimer
of molecular formula C10H12. This reaction occurs slowly at room temperature and is sped up by
heating. What is the structure of the product of this reaction? Clearly indicate stereochemistry, if
any.
heat
or
C10H12
Diels-Alder reaction to give a product of endo addition
H
H
Chem 40B SS2 2022
Midterm
Q1_________(8 points)
Q2_________(20 points)
Q3_________(24 points)
Q4_________(14 points)
Q5_________(30 points)
-Q6_________(15 points)
Q7_________(15 points)
Q8_________(24 points)
Total_________(150 points)
Printed Name_______________________
Signature__________________________
PID______________________________
1. NMR Spectroscopy (8 points).
A. Label the equivalent sets of hydrogens in the molecules below and state clearly how many different
resonances you expect in the 1H NMR spectrum (2 pts each).
O
Cl
O
Cl
B. Label the equivalent sets of carbons in the molecules below and state clearly how many different
resonances you expect in the 13C NMR spectrum (2 pts each).
O
OH
2. Structure Elucidation (20 points) From the spectral data on this page, deduce the structure of the
compound. Label each resonance in the 1H and 13C NMR spectra. The molecular formula of the
compound is C5H7NO2.
Solvent peaks
– ignore
TMS
standard
TMS
standard
3. Alkenes (24 points). Show 8 transformation of 1,2-dimethylcyclobutene. Include stereochemistry as
appropriate. Where new stereochemistry is formed, indicate whether the reaction involves syn or anti
addition or neither. If enantiomers are formed, only one enantiomer may be shown.
4. Alkyne Chemistry (14 points). Draw 7 reactions of 2-pentyne. Clearly indicate stereochemistry, if
any.
5. Chemical Reactions (30 points). Draw the organic products of the following reactions, being
mindful of stereochemistry. In reactions that form enantiomers, draw only one of the two
enantiomers.
Cl2
A.
excess H2
B.
Pd
two diastereomeric products
1) excess BH3
C.
2) excess H2O2
NaOH/H2O
two diastereomeric products
D.
OsO4
H 2S
Br2 / H2O
E.
O
heat
O
F.
O
heat
G.
CN
1) NaNH2
2) CH3CH2Br
H.
H 3C C C H
3) H2 / Lindlar catalyst
COOCH3
1)
heat
I.
2)
F3C
O
O
O
H
Na / NH3
J.
two diastereomeric products
6. Reaction Mechanisms (15 points). Provide reasonable mechanisms for the three reactions below. Each
part is worth 5 points.
HO
A.
H + / H 2O
OH
H + / H 2O
B.
OH
C.
Br2
O
Br
7. Synthesis (15 points). Provide reasonable methods for the synthesis conversions below. More than
one step may be involved. You may use any organic or inorganic reagent. Each part is worth 5
points.
Br
Br
A.
OH
CHO
B.
CHO
C.
H C C H
8. Challenge Question (24 points). Do one of the two problems below. Clearly indicate which part you
want graded by circling the letter corresponding to the problem.
A. Provide a reasonable method for the synthesis conversion below. You may use any organic or
inorganic reagent.
COOCH2CH3
H C C C C H
OH
OH
B. Provide a reasonable mechanism for the transformation below.
2 Br2
HO
O
Br
OH
Br
O