practice questions (from old exams) for the final exam...
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1
Practice questions (from old exams) for the Final Exam, with answers
Spectral Data – Ranges are Approximate
1H NMR δ 13C NMR δ RCH3 .9-1.2 C-I 0-40 R2CH2 1.1-1.4 C-Br 25-65 R3CH 1.5 C-Cl 35-80 C=C-H 4.5-6.5 -CH3 8-30 C≡C-H 2-3.5 -CH2- 15-55 Ar-H 6-8.5 R3C-H 20-60 ArC-H 2.2-3 ≡C 65-85 C=C-C-H 1.5-1.9 =C 80-170 H-C-F 4-4.5 C-O 40-80 H-C-Cl 3-4 C=O 170-210 H-C-Br 2.5-4 C in Ar 110-165 H-C-I 2-4 C-N 30-65 H-C-OH 3.4-4 C-C=O 20-60 H-C-OR 3-4 O-C-O 90-110 RCOO-C-H 3.7-4.5 H-C-CO2R 2-2.4 H-C-CO2H 2-2.6 O-CH-O 4-5.5 H-C-C=O 2-3.5 RC(H)=O 9-10 RO-H 1-5.5 RCO2-H 10.5-12 RN-H 1-5 IR cm-1 C-H (alkanes) 1850-2900 C-H (alkenes) 3020-3080 C-H (aromatic) 3000-3100 C=C 1620-1680 ≡C-H 3100-3300 C≡C 2100-2260 C-O 1080-1300 C=O 1650-1800 O-H 3610-3640 (alcohol) 3200-3600 (acid) N-H 3300-3500 C≡Ν 2210−2260 ΝΟ2 1515−1560 1345−1385 C-Cl 750 - 850
2
Below are some useful pKa values for the underlined protons:
Acid pKa Acid pKa
RO
O
H
R2N
O
H
O
H
30
25
20
O O
H
O
OR
O
H
RO
O
OR
O
H
13
11
9
NH40
19
17
t-BuOH
EtOH
5O
O
H
N C H 9
R N
O
H
H
24
3
1. Which amino acid might play a role in proton transfer within an enzyme’s active site (in a protein)?
NN
H O
HH
N
NH
NN
O
HH
NN
H O
HH
NN
H O
HHH
(d)(c)(b)(a)
2. The mechanism for the DCC-mediated amino acid coupling of 1 with 2 is shown
below:
BOCHNOH
O
R
H2NOCH2Ph
O
R1
DCC
N C NCy
Cy
BOCHNO
–
O
R
H2NOCH2Ph
O
R1
BOCHNO
OH
R
N
NH
Cy
CyN
PhCH2O H
O
R1
N
C
NCy
CyH
BOCHNN
OCH2Ph
R
O
H
R1
O
BOCHNO
O
R
N
NH
Cy
Cy
BOCHNN
OCH2Ph
R
O
H
R1
O
N N
O
H H
+
1 2 3
Mechanism:
1 +
+
5 6 7
+
2 8 3
+
9
4
Which atom(s) in the starting materials would have to be labeled with 18O in order to prepare completely 18O-labeled 9?
4
BOCHNOH
O18
R
H2N OCH2Ph
O18
R1
BOCHNO18H
O
R
H2N O18CH2Ph
O
R1
BOCHNOH
O
R R1
H2N O18CH2Ph
O18
BOCHNO18H
O18
R
H2N OCH2Ph
O
R1
1 2
(b)
1 2
(d)
1 2
(a)
1 2
(c)
3. Amino acids 1 can be polymerized via their N-carboxyanhydrides 2 to furnish
polypeptides 3.
H2N
O
OH
R
+N
O
O
OH
R
1 2
H
NN
OH
O
R
H
O
R
Hn
n
3
Which atom indicated below in 1 or 2 (labeled ((a) – (d)) serves as the electrophilic center in this transformation?
H2N
O
OH
R
+N
O
O
OH
R
1 2
n
(a) (b) (c) (d)
5
4. Which orientation would cholesterol most likely adopt within a cell membrane?
HOHO
HO
OHHO
cholesterol
HO
(a) (b) (c) (d) 5. Mixing the eight atomic p orbitals in the tetraene below generates ___ new
molecular orbitals?
a) 2 c) 8 b) 4 d) 16
6. The Diels Alder reaction shown below furnishes primarily
OCH3
Cl
CO2CH3H3CO2C
OCH3
CO2CH3
Cl
CO2CH3OCH3
CO2CH3
Cl
CO2CH3OCH3
CO2CH3
ClCO2CH3
OCH3
CO2CH3
ClCO2CH3
+
(a) (b) (c) (d)
heat
6
7. Like a Diels Alder [4π + 2π] cycloaddition, the unsaturated compounds tropone (1,
6π) and cyclopentadiene (2, 4π) undergo a concerted [6π + 4π] cycloaddition. Two [6π + 4π] cycloadducts are possible: the endo adduct 3 or the exo adduct 4. In this reaction, the major participating orbitals are the LUMO of tropone and the HOMO of cyclopentadiene shown below.
O
O
+
O
23 endo
heat
1
O
4 exo
or
LUMO of tropone HOMO of cyclopentadiene
Which statement is true? (Hint: Examine secondary orbital interactions in the transition states preceding 3 and 4.)
a) The endo adduct 3 is favored. b) The exo adduct 4 is favored. c) Both 3 and 4 will be formed with little preference. d) The preference between 3 and 4 cannot be predicted from this information.
7
8. Predict the product from the following reaction.
Ph
O(H3C)2CuLi
Ph
O
CH3
Ph
O
CH3
Br
Ph
OCH3
Ph
OCH3
(a) (b) (c) (d)
9. The competition between enolate alkylation and base-induced E2 elimination with
H3CCH2-I electrophile is finely balanced. Amide enolates give a better ratio of alkylation-to-elimination compared with ketone enolates because
a) ketone enolates are more nucleophilic, but both enolates are similarly basic. b) amide enolates are more nucleophilic, but both enolates are similarly basic. c) amide enolates are more basic, but both enolates are similarly nucleophilic. d) ketone enolates are more basic, but both enolates are similarly nucleophilic.
10. Which enolate is most stable?
O–
O2NO–
O2N
O–
H3COO–
H3CO
(a) (b) (c) (d)
11. Which structure is consistent with the following 1H NMR information?
δ 7.2 5H, broad singlet (broad because of overlapping signals) δ 3.5 3H, singlet δ 2.4 2H, triplet, J = 8 Hz δ 2.2 2H, triplet, J = 8 Hz
O
OCH3H3C
O
OCH3
O
OCH2CH3 H3CCH2CH2O
O
(a) (b) (c) (d)
8
12. Treatment of ammonia (1) with a large excess of bromoethane (2) in the presence of excess base (to sop up the HBr generated) will form
NH3 H3C Br+
base
H3C NH2 H3C N CH3N
H3C CH3
N
CH3H3C
H3C
++
(a) (b) (c) (d)
1 2
Br– Br–
13. Treatment of the aldehyde ester 1 with excess DIBAL (diisobutylaluminum
hydride, i-Bu2Al-H) at low temperature, followed by an aqueous acid quench, affords
O
HO
OCH3i-Bu2Al-H
OH
O
OCH3OH
OH
H3O+
OH
O
HO
HO
H
1
excess
low temp.
quench
(a) (b) (c) (d) 14. What would you expect for the isoelectric point of lysine?
OHH2N
O
NH2 a) 0, b) < 6, c) ~ 6, d) > 6
15. Which of the following hydrocarbon acids will be a constituent of the highest
melting fat?
(a)
(b)
(c)
(d)
HO
O
HO
O
HO
O
HO
O
9
16. Which of the following compounds would be appropriate for the synthesis of valine
by the Strecker amino acid synthesis?
(a) (b) (c) (d)
? H2NOH
O1) NH3, H
+, CN
-
2) H+, H2O heat
H O HO O
O
H
O
OH
17. Part of the mechanism of acetal formation is shown below:
H
H3CO OCH3
+ CH3OH+ H+
H
H3CO OH+
H
H
O
1 2 3 4
H
OH
+ steps
RR
R R
For which R group will the second step (2 to 3) be the fastest?
a) R = OCH3, b) R = H , c) R = CH3, d) R = NO2 18. Which is the best method to prepare compound 1?
MeO2C CO2Me
1)
2) H+, H2O, heat
BrBr
MeO2C CO2Me
CO2Me
CH3-CO2Me1) NaOMe
2)
MeO2C CO2Me CO2MeMeO2C CO2Me CH3-CO2Me
BrBr
(a)
(b)
(c)
(d)
+
1
+
cat.NaOMe
cat.NaOMe
-
10
19. Which of the following species corresponds to the open chain form of the following sugar?
O
OH
OH
OH
HO
(a) (b) (c) (d)
OH
O
OHH
HH
OH
OH
H
O
OHH
HH
OH
OH
H
H
H
OH
O
OHH
HHO
H
OH
H
O
HHO
HH
H
OH
HO
H
20. Which of the following compounds is NOT a possible product of the reaction of
compound 1 with base (followed by acid quench)?
O
O
EtO
O
O
O
EtO
O
O
O
O
O
EtO
O
O
O
EtO
(a) (b) (c) (d)
1) NaOEt
2) H3O+
1
11
21. Treating compound 1 with a weak base produces a change in stereochemistry at the alcohol (from cis-to-the-methyl to trans-to-the-methyl). This transformation is probably due to
MeOHO
H
MeOHO
H
cat.
NaOEt
EtOH
1 2
cis trans
a) a reverse aldol reaction, followed by a normal aldol reaction from the opposite
side of the intermediate aldehyde. b) dehydration of water followed by conjugate addition of water from the opposite
side of the intermediate enone. c) enolization of the ketone and reprotonation by the solvent (EtOH) from the
opposite side of the intermediate enolate. d) backside displacement of the alcohol by the EtO – followed by hydrolysis of
the ethyl group.
22. The following sequence affords
CH3
OH
O 1) Br2, PBr3
2) H2O3) CH3NH2
a) a mixture of chiral, diastereomeric amino acids. b) a mixture of racemic, diastereomeric amino acids. c) a chiral amino acid product. d) a racemic amino acid product.
23. How many peaks would you expect to see in the 13C NMR spectrum of the following compound?
H3C
OH
a) 3, c) 6, b) 5, d) 8
12
24. What is the product of the addition of ethanol (1) to cyclohexanone (2) under acidic conditions?
CH3CH2OH
OH
+
HO OCH2CH3 H3CH2CO OCH2CH3 H3CH2C CH2CH3
(a) (b) (c) (d)
1 2
+
A solution of cyclohexanonein ethanol
25. Which of the indicated protons is the most acidic?
O
N
O
H
HHO
O
H
H
(a)
(b)
(c)
(d)
26. Initiation, propagation and termination are all characteristics of which of the
following processes?
a) Reductive amination. b) Step growth polymerization. c) Chain growth polymerization. d) Glycosylation.
27. Which amino acid has a basic side chain functionality?
H3NO–
O+
O NH2
(a)H2N
O–
O
+(b) H3NO–
O+
O OH
(c) H3NO–
O+
NH
(d)
NH
NH2
13
28. The preparation of a chiral amino acid 1 is shown below:
OH
R
O 1) Br2;PBr3
2) H2OOH
R
O
Br NH3OH
R
O
H2N
O
O O
pyridineOH
R
OHN
O
1) lipase-mediated hydrolysis
2) separate amine from amide
OH
R
O
H2N1
A B
C Dchiral
At which stage of the sequence is a single enantiomer produced?
a) A b) B c) C d) D 29. The amino acid valine (1) is most likely to
HN
NH
O
1
remainderof proteinremainder
of protein
a) participate in a chemical transformation in an enzyme's active site. b) assist in proton transfer reactions during catalysis. c) occupy a position in the interior of a protein. d) occupy a position on the surface of a protein.
30. Which molecular orbital picture corresponds to π* (a pi antibond)?
(a) (b) (c) (d)
31. Which diene will not participate in a Diels Alder reaction?
a) b) c) d)
14
32. The regiochemical orientation of the substituents X and E in the cyclohexene formed upon Diels Alder reaction is
E
E = electron withdrawing group
+
X
X = electron donating group
a)
E
X
b)
E
c)
E
d)
EX
X
X
33. The stereochemical outcome of the Diels Alder reaction shown below is controlled
by secondary orbital interactions between atoms
CH3
+
O
H
21 3
4
a) 1 and 4. b) 1 and 3. c) 2 and 4. d) 2 and 3.
34. Heating triene 1 promotes an intramolecular Diels Alder reaction to furnish
CH3
O
1
OH CH3
a)
OH CH3
b)
H3CH O
c)
H3CH O
d)
15
35. Robinson annelation of the 13C-labeled ketoester 1 and methyl vinyl ketone 2
furnishes
O
CO2CH3
O
CO2CH3
O
CO2CH3
O
CO2CH3
OO
CO2CH3
+
1 2
13C label
13C label
a)
13C label
b) c)
13C label
d)
13C label
36. Treatment of ketoester 1 with excess diisobutylaluminum hydride (DIBAL) at low
temperature, followed by an aqueous acid quench, produces
O
CO2CH3
OH
CO2CH3
O
CHO
H3O+
OH
CHO
OH
OH
DIBAL
low temp. quench
1
a) b) c) d)
37. Reductive amination of cyclohexanone 1 with the valine derivative 2 affords
O
H2NOCH3
O
NaBH3CN
AcOH
HN
OCH3
O
NOCH3
O
H2N
O O HN
OCH3
O
O
1
+
2
a) b) c) d)
16
38. Which structure best matches the following 1H NMR spectrum (integration given above signals)?
TMS
H3C
CH2OH
H3C
OCH3
H3C
OCH3
H3C
CH2OH
012345678
!
2
3 3
2
a) b) c) d)
39. Treatment of ketone 1 with 1 equivalent of LDA, and then 100 equivalents of
methyl acrylate (2), will generate
O
CO2CH3
CO2CH3
O
O O
O CO2CH3
O
CO2CH3
1
1 equiv.
LDA
100 equiv.
2
a)
b)
c)n
d) n
17
40. The equilibrium constant Keq for the following transformation is
HO CNO
CN
Keq
a) 1 b) 0 c) < 1 d) > 1
41. Rank (fastest-to-slowest) the following carboxylic acid derivatives in terms of their
rate of nucleophilic addition.
R NH2
O
I
R Cl
O
II
R OCH3
O
III
R O
O O
R
IV
a) II > IV > III > I c) I > III > IV > II
b) II > III > IV > I d) I > IV > III > II
42. Which carboxylic acid will have the lowest pKa?
CO2H
OCH3
CO2H
NO2
CO2H
NO2
CO2H
OCH3a) b) c) d)
18
43. Which pyranose corresponds to the Haworth projection shown below?
44. Treatment of lipid 1 with excess LiAlH4, followed by an aqueous acid quench, provides
O
O
O
OO
OLiAlH4
OH
HO OH
HO
OH
HO OH
HO
H3O+
OH
OH
HO
HO
OH
HO
HO
OH
quench
a)
+
b)
+
c)
+
d)
+
O
HO
H
HO
OH
H
H
OH
H
OH
OOH
HOHO
HO
OH
H
a)O
OH
HOHO
HO
H
OH
b)O
OHHO
HO
HO
H
OH
c)O
OHHO
HO
HO
OH
H
d)
19
45. Many glycoproteins are joined between the polypeptide portion and the polysaccharide portion with an asparagine connection:
othersugars remainder
of proteinO H
N
OHHOO
O-H
asparagine
remainderof protein
O HN
O
Formation of the indicated connection (arrow) proceeds through a process that is mechanistically similar to a) mutarotation, c) nucleophilic acyl substitution, b) glycosylation, d) reductive amination.
46. Which polymer is a good model for understanding the physical properties (e.g., melting point) of fats (= triacyl glycerols)?
a) nylon NH
HN
O
O n
b) polyethylenen
c) teflon
n
F
FF
F
d) polyurethane
NH
HN
O
OO
O n
H
H
H
H
47. Which of the following lipids might be effective at membrane formation?
O
O
O
O
O
PO
O
– O
N+
O
O
O
O
O
PO
O
H3CO
N
O
O
O
O
O
PO
O
– O
N+
O
O
O
O
O
PO
O
H3CO
N
a)
b)
c)
d)
20
48. Where is water most likely to be found when in the vicinity of a bilayer membrane?
a)
H2O
b)
H2O
c)
H2O
d)
H2O