Section 001 = Lee Section 002 = Kerr The exam code is found on the first page of the exam
Chemistry 223b Midterm Test Saturday, March 8, 2008 Duration: 2.00 hours
• This exam contains 40 questions of equal weight, and there is no penalty for incorrect answers. Be sure you have a complete exam paper. Scrap paper is attached, and it may be detached for use.
• Place your student ID card on your desk.
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• Use of a molecular model set is permitted. However, the sharing of models or model pieces is strictly forbidden. Place the model set on your desk and open the box.
• Carefully transfer your answers to the Scantron sheet by filling in the appropriate bubbles with pencil. The answers on your Scantron sheet are considered to be your official answers, so please ensure that you have transferred them accurately.
• You are welcome to keep the exam booklet and any scrap sheets. • The exam is to be done individually. Proctors and instructors will not interpret,
translate, clarify, or explain exam questions, nor will they confirm, verify, or assist you with your answers or your thinking.
• There is no time allotted for filling in the Scantron. After exactly two hours, everyone must put their pencils down and close their booklets. The Scantron will be collected, whether completed or not.
• If you do not leave before the last 15 minutes, you must stay in your seat until
you are dismissed. NO TALKING IS ALLOWED AT ANY TIME.
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Chemistry 223b Midterm, March 2008 Page 1
Please ensure that you have entered code 111 on your answer sheet. 1. Suppose Schrodinger owned a big, fluffy cat that appeared white under sunlight.
If the cat was placed in a room that was illuminated with only green light, what colour would the cat appear?
A) Red B) Green C) White D) Black E) Violet
2. Which one of the following molecules has the smallest HOMO-LUMO gap?
A)
B)
C)
D)
E)
Chemistry 223b Midterm, March 2008 Page 2
3. The spectral data produced by a UV-visible spectrometer is typically a plot of…
A) Fluorescence as a function of time B) Fluorescence as a function of wavelength C) Absorbance as a function of wavelength D) Absorbance as a function of fluorescence E) Wavelength as a function of time
4. What is the non-radiative photophysical process indicated below?
S0
S1
T1
A) Phosphorescence B) Vibrational cooling C) Excitational cooling D) Internal conversion E) Fluorescence
Chemistry 223b Midterm, March 2008 Page 3
5. The coloured form of the acid-base indicator phenolphthalein has two negative charges. Which one of A – E is NOT a correct resonance structure of the rest?
A) OO
O
O
B) OO
O
O
C) OO
O
O
D) OO
O
O
E) OO
O
O
Chemistry 223b Midterm, March 2008 Page 4
6. Which part of the cell uses an adenine residue to catalyze a nucleophilic acyl substitution reaction between a mixed anhydride and an amino group?
A) Lysosome B) RNA polymerase C) Chymotrypsin D) ATP synthase E) None of the other answers are correct
7. Which two of the following are most likely to be found in the outer membrane of
Gram-(−) bacteria?
1. Peptides 2. Carbohydrates 3. Lipids 4. Nucleic Acids
A) 2 and 3 B) 2 and 4 C) 1 and 3 D) 1 and 2 E) 3 and 4
Chemistry 223b Midterm, March 2008 Page 5
8. What is the predominant form of lysine at pH 12?
A)
H2N CH C
CH2
OHO
CH2
CH2
CH2
NH2
B)
H3N CH CCH2
OH
O
CH2
CH2
CH2
NH3
C)
H2N CH C
CH2
OO
CH2
CH2
CH2
NH2
D)
H3N CH CCH2
O
O
CH2
CH2
CH2
NH3
E)
HN CH CCH2
OO
CH2
CH2
CH2
NH
Chemistry 223b Midterm, March 2008 Page 6
9. Which one of the following statements about α-amino acids is NOT correct?
A) Most natural amino acids have the L configuration and are S B) The pKa of the COOH group is higher than that of a normal carboxylic acid
due to stabilization of the conjugate base by the α-amino group C) Amino acids are very soluble in acidic and basic solutions D) At neutral pH, they are usually not very soluble in water E) They are amphoteric
10. The tertiary structure of a protein refers to…
A) The arrangement of the peptide into a β-sheet B) The presence of heme molecules bound to protein C) The interaction of protein subunits D) The way the protein folds over on itself
E) The arrangement of the peptide into a α-helix 11. Which one of A – E is least likely to be involved in the mechanism of the following
reaction?
O
R NHR'
H+ / H2ORCOOH + H3NR'
A) R NH2R'
HO OH
B)OH
R NHR' C)
O
R NH2R'
D) OH
R NHR'
E)
R NHR'
HO OH2
Chemistry 223b Midterm, March 2008 Page 7
12. Which one of the following statements is NOT correct regarding the use of HPLC for the determination of amino acid composition?
A) The identity of the amino acid can be determined by the retention time. B) Molecules that adhere strongly to the stationary phase of the chromatography
column will have a higher retention time. C) A sample of hydrolyzed protein is injected into the HPLC. D) The amino acids are combined with ninhydrin to form purple complexes,
which are then separated by the chromatography column. E) The relative quantities of the amino acids can be determined by comparing
the relative areas of the absorption peaks. 13. Which one of A – E is least likely to be involved in the mechanism of the following
reaction?
O
R R'R" NH2+
NR"
R R'
H+ / H2O
A)
R R'
H2O NHR''
B)
R R'
HO NH2R''
C)NHR''
R R'
D) OH
R R'
E)NH2R''
R R'
Chemistry 223b Midterm, March 2008 Page 8
14. Which of A – E is/are proper resonance structure(s) of Ruhemann’s Purple, which is formed when two equivalents of ninhydrin react with an amino acid?
O
O
O
2
amino acid?
N
O
O
O
O
N
O
O
O
O
N
OH
O
O
O
N
OH
O
O
O
N
O
O
O
O
2
5
1
43
A) 2 and 5 B) 5 only C) 1 and 4 only D) 2 and 3 only E) 3 and 5 only
Chemistry 223b Midterm, March 2008 Page 9
15. Sanger analysis of an unknown peptide gave one equivalent of the molecule on the left and two equivalents of the one on the right.
COOH
NH
O2N NO2
COOH
H2N
NH
NO2
O2N
What could the peptide be? 1. Lys-Phe-Lys-Ala-Val 2. Val-Gly-Ser-Lys-Lys 3. Gly-Pro-Lys-Lys-Phe-Val 4. Lys-Val-Ala-Tyr-Lys 5. Val-Glu-Lys-Lys-Ala
A) None of them B) 1 and 4 only C) 5 only D) 2 and 5 only E) 1 and 3 only
Chemistry 223b Midterm, March 2008 Page 10
16. The compound below was the first phenylthiohydantoin to be isolated from an Edman degradation. What could the peptide be?
HNN
S
O 1. Phe-Gly-Cys-Pro 2. Cys-Pro-Phe-Gly 3. Gly-Pro-Cys-Phe 4. Pro-Gly-Phe-Cys
A) 2 and 3 only B) 1 and 4 only C) 1 and 3 only D) 2 only E) 3 only
17. What does the term graduated acid lability best refer to?
A) The different sensitivities of acid derivatives towards destruction by acid. B) The presence of many different functional groups of varying pKa values in an
enzyme active site. C) The varying abilities of acids to protonate leaving groups. D) The volumes occupied by the same mass of different amino acids are large
enough to be measured using a graduated pipette. E) The relationship between acid strength and conjugate-base stability
Chemistry 223b Midterm, March 2008 Page 11
18. Which of A – E is/are least likely to be involved in the following reaction?
N
O
NH
O
R
N C N
N
O
NH
OR
HNR'
N C NHO
H
O
R O
O
R OHH2N R'
O
R NHR'
1 2 3
4 5
+
N C N
A) 1 and 5 only B) 3 only C) None (all of 1 – 5 are involved) D) 4 only E) 2 only
Chemistry 223b Midterm, March 2008 Page 12
19. Consider the following solid-phase peptide synthesis. Assume that each DCC coupling step proceeds in 90% yield. Assume that all of the other steps proceed in 100% yield. What will be the approximate distribution of products?
O
ONH2
HO
ONH
BOC
HO
ONH-BOC
O
ONH
O HN
ONH-BOC
HBr / HOAc
HO
ONH
O HN
ONH3
+ DCC, then rinseO
ONH
ONH-BOC
1. TFA, then rinse2. Et3N, then rinse
3.
+ DCC, then rinse
A) Leu-Ala-Val (73%), Ala-Val (18%), Leu-Val (8%), Val (1%) B) Leu-Ala-Val (81%), Ala-Val (9%), Leu-Val (9%), Val (1%) C) Leu-Ala-Val (90%), Ala-Val (5%), Leu-Val (4%), Val (1%) D) Leu-Ala-Val (90%), Val (10%) E) Leu-Ala-Val (81%), Ala-Ala-Val (9%), Leu-Leu-Val (9%), Val (1%)
Chemistry 223b Midterm, March 2008 Page 13
20. What is the purpose of the BOC protecting group?
A) To decrease the nucleophilicity of the amino group B) To convert the amino group into a better leaving group C) To increase the electrophilicity of the amino group D) To increase the nucleophilicity of the amino group E) To decrease the electrophilicity of the amino group
21. Which statement does NOT correctly describe the current state of the
chymotrypsin-substrate complex below and the next mechanistic step that occurs?
Asp
OO
His
N N O
N
O
R1
Ser
R2
H
HH
NH
A) The function of Asp is to hold the imidazole ring of His in the proper orientation.
B) The product formed from the next step is known as an acyl enzyme. C) In the next step, the C-terminal fragment of the original substrate departs. D) In the next step, histidine protonates the serine oxygen. E) The aromatic ring interacts with the enzyme via hydrophobic interactions.
Chemistry 223b Midterm, March 2008 Page 14
22. Which statement(s) is/are CORRECT about this enzyme-catalyzed reaction?
O
OHOH
OPO
O
OPO
O
OPO
O
O
N
NN
N
NH2
H2NO
O
R1
O
OHOH
OPO
ON
NN
N
NH2
H2NO
O
R1OP
O
OOP
O
OO
1. Mg2+ coordinates to the carboxylate group to make it a better electrophile 2. An O− bonded to phosphorous is the nucleophile 3. A tetrahedral intermediate is formed during the reaciton
A) None of the statements are correct B) 3 only C) 2 only D) 2 and 3 only E) All the statements are correct
Chemistry 223b Midterm, March 2008 Page 15
23. Which of the following is/are NOT D-fructose?
HOH2C
OH
HO OH
CH2OHO O
OHOH
HO
OH
CH2OH
HOH2CO
OH
HO
OH
CH2OHHOH2C
O
OH
HO
OH
CH2OH
1 2
3 4
A) 4 B) 2 C) 3 D) 1 E) All are D-fructose
24. Consider any given D-aldohexose. If we invert only the configuration of the
penultimate carbon, which one of the following statements is NOT correct?
A) The new compound is an L-aldohexose B) The new compound will rotate plane-polarized light to the same magnitude
but in the opposite direction C) The new compound is an epimer of the original one D) The new compound is a diastereomer of the original one E) The new compound will have a different common name
Chemistry 223b Midterm, March 2008 Page 16
25. What is a correct name for the sugar below?
CHO
NHHOHH
HHHO H
CH2OH
C
O
CH3
A) 2,4-dideoxy-2-N-acetylamino-L-gulose B) Both 2,4-dideoxy-2-N-acetylamino-L-allose and
2,4-dideoxy-2-N-acetylamino-L-gulose are correct C) 2,4-dideoxy-2-N-acetylamino-L-allose D) 4-deoxy-2-N-acetylamino-L-talose E) 2,4-dideoxy-2-N-acetylamino-L-mannose
26. A 1.0 M solution of the pure α-anomer of a certain sugar has an optical rotation
of +120°. A 1.0 M solution of the pure β-anomer of the same sugar has a rotation of +50. If a solution contains 0.5 M of the α anomer and 0.5 M of the β anomer, what is the optical rotation of the mixture?
A) +35° B) +85° C) +70° D) +170° E) The mixture would be optically inactive, because it is a racemic mixture
Chemistry 223b Midterm, March 2008 Page 17
27. Which mechanistic step in the formation of methyl D-glucopyranoside is NOT correct?
OHO
HOOH
OH
OH
H
CH3OH
OHO
HOOH
OH
OCH3
H
OHO
HOOH
OH
OCH3
OHHO
HOOH
OH
H
OH
1
OHO
HOOH
OH
OH
2
H
OHO
HOOH
OH
OH24
35
A) 3 B) 1 C) 5 D) 4 E) 2
Chemistry 223b Midterm, March 2008 Page 18
28. Which of the following are α-glycosides?
O
OH
OHHO
HOH2C
HO
OCH3O
OH OH
HOH2CO
OH OOH
OH
OHO
OHOH
HOH2C
N
OH
1 2 3
5
OHOH
OHO
H
HOHO
4
A) 3 and 4 only B) 3, 4, and 5 only C) 2, 3, and 5 only D) 2 and 3 only E) 1 and 4 only
29. The reactions of aldehydes and ketones with alcohols, hydride reducing agents,
amines, enolates, and cyanide are classified as which type of chemical reaction?
A) Hydrolysis B) Electrophilic addition C) Electrophilic substitution D) Nucleophilic acyl substitution E) Nucleophilic addition
Chemistry 223b Midterm, March 2008 Page 19
30. Which one of the following is D-galactonic acid?
A)
COOHOHH
HHOHHOOHH
COOH
B)
COOH
OHHHHO
HHOOHH
CH2OH
C)
COOH
HO HH OH
H OHHO H
CH2OH
D)
COOH
OHHHHO
OHHOHH
CH2OH
E)
CHOOHH
HHOHHOOHH
COOH
31. When D-fructose is reduced with NaBH4 or LiAlH4, what is the relationship
between the two products that are formed?
A) Constitutional isomers B) Enantiomers C) Diastereomers D) Anomers E) Tautomers
Chemistry 223b Midterm, March 2008 Page 20
32. The two compounds below can be described as….
1. Tautomers 2. Epimers 3. Constitutional isomers
A) 1 and 3 only B) 2 only C) 1 only D) 3 only E) 2 and 3 only
33. Which one of A – E least likely to be formed from the aldol reaction of
glyceraldehyde with itself?
A)
CHOOH
HHOH OH
CH2OH
HOH2C
B)
CHOHO
HHOH OH
CH2OH
CH2OH
C)
CHOHO
H OHH OH
CH2OH
CH2OH
D)
CHOOH
H OHHHO
CH2OH
HOH2C
E)
CHOOH
H OHH OH
CH2OH
HOH2C
NH NH2
Chemistry 223b Midterm, March 2008 Page 21
34. A mechanism for the acid-catalyzed acetylation of a modified sugar is shown below. Which step(s) of the mechanism is/are NOT correct?
OOH
H3COOCH3
OCH3O
O
H3COOCH3
OCH3
O
O
O
O OH
O
O
O
OH
H3COOCH3
OCH3
H+
1
O
O
O
H+
OH
O
O
2
O
HO
H3COOCH3
OCH3
O
OH
O
3
O
O
H3COOCH3
OCH3
O
O
O
H3COOCH3
OCH3
OH
A) 3 only B) 2 and 3 only C) 1 and 2 only D) 1 only E) None are incorrect (all are correct)
Chemistry 223b Midterm, March 2008 Page 22
35. The Kiliani-Fischer synthesis of a monosaccharide from a D-aldopentose gave D-galactose and D-talose as the products. What was the D-aldopentose used?
A) Ribulose B) Arabinose C) Xylose D) Ribose E) Lyxose
36. What are the two glycosidic linkages in the compound below?
OH
OH
OH
O
HO
O
OH
OH
HO
HOO
1
2
1 2
A) α(2,1) β(1,5)
B) α(2,1) β(1,2)
C) β(2,1) α(2,1)
D) β(1,2) α(1,2)
E) α(1,4) β(1,5)
Chemistry 223b Midterm, March 2008 Page 23
37. Which one of the following compounds is expected to be more soluble in aqueous Na2CO3 than in pure water or in dichloromethane?
A)
O N
N
N
HN
O
B)
O N
N
N
N
O
C) HO
OH
O
O
D) O
OH
OH
OH
E)
O
OHOH
38. Caffeine has no visible colour, but when it is spotted on a TLC plate, a spot is
observed when the plate is placed under a UV lamp. Which one of A – E correctly explains this phenomenon?
A) Caffeine absorbs UV light, preventing it from reaching the dye on the plate B) Caffeine transmits UV light, which illuminates the spot on the plate C) Caffeine reacts with the TLC plate in the presence of UV light D) Caffeine absorbs UV light and fluoresces E) Caffeine reflects UV light
Chemistry 223b Midterm, March 2008 Page 24
39. Which of the following statements is/are correct?
1. The acetyl group of N-acetylphenylalanine is bonded to the original carboxyl group of the amino acid.
2. The D,L notation in D,L-phenylalanine indicates the compound is a 1:1 mixture of D and L enantiomers.
3. Amphoteric compounds can behave as both acids and bases. 4. At pH 7, the side chain of arginine is uncharged.
A) 1 and 2 only B) 3 only C) 2 and 3 only D) 3 and 4 only E) All statements are correct
40. What is the approximate volume of liquid delivered by a full squirt of a standard,
disposable Pasteur pipette?
A) 0.10 – 0.15 mL B) 8 – 10 mL C) 1 – 2 mL D) 18 – 20 mL E) 50 – 70 mL
Appendix 1: D-Aldoses
CHO
CH2OHOHH
CHO
H OHCH2OH
OHHCHO
H OHCH2OH
HHO
CHOOHH
H OH
CH2OHOHH
CHOHHO
H OH
CH2OHOHH
CHOOHH
HO H
CH2OHOHH
CHOHHO
HO H
CH2OHOHH
CHOOHH
H OHCH2OH
OHHH OH
CHOOHH
H OHCH2OH
OHHHO H
CHOOHH
H OHCH2OH
HHOH OH
CHOOHH
H OHCH2OH
HHOHO H
CHOHHO
H OHCH2OH
OHHH OH
CHOHHO
H OHCH2OH
OHHHO H
CHOHHO
H OHCH2OH
HHOH OH
CHOHHO
H OHCH2OH
HHOHO H
Glyceraldehyde
Erythrose Threose
Ribose Arabinose Xylose Lyxose
Allose Altrose Glucose Mannose Gulose Idose Galactose Talose
Appendix 2: D-Ketoses
CH2OH
CH2OH
O
CH2OH
O
CH2OH
OH
CH2OH
O
OH
OH
CH2OH
CH2OH
O
HO
OH
CH2OH
CH2OH
O
OH
OH
CH2OH
OH
H
H
H H
H
H
H
H
CH2OH
O
HO
OH
CH2OH
OH
H
H
H
CH2OH
O
HO
HO
CH2OH
OH
H
H
H
CH2OH
O
OH
HO
CH2OH
OH
H
H
H
dihydroxyacetone
D-erythrulose
D-ribulose D-xylulose
D- psicose D-fructose D-sorbose D-tagulose
CH2OH
CH2OH
O
CH2OH
O
CH2OH
OH
CH2OH
O
OH
OH
CH2OH
CH2OH
O
HO
OH
CH2OH
CH2OH
O
OH
OH
CH2OH
OH
H
H
H H
H
H
H
H
CH2OH
O
HO
OH
CH2OH
OH
H
H
H
CH2OH
O
HO
HO
CH2OH
OH
H
H
H
CH2OH
O
OH
HO
CH2OH
OH
H
H
H
dihydroxyacetone
D-erythrulose
D-ribulose D-xylulose
CH2OH
CH2OH
O
CH2OH
O
CH2OH
OH
CH2OH
O
OH
OH
CH2OH
CH2OH
O
HO
OH
CH2OH
CH2OH
O
OH
OH
CH2OH
OH
H
H
H H
H
H
H
H
CH2OH
O
HO
OH
CH2OH
OH
H
H
H
CH2OH
O
HO
HO
CH2OH
OH
H
H
H
CH2OH
O
OH
HO
CH2OH
OH
H
H
H
dihydroxyacetone
D-erythrulose
D-ribulose D-xylulose
D- psicose D-fructose D-sorbose D-tagulose
Appendix 3: Amino-acid side chains
CH3H CH CH3
CH3
CH CH3
CH2
CH3
CH2
CH CH3
CH3
CH2 CH2
OH
CH2
HN
CH2
CH2
S
CH3
CH2
N
NH
CH2
OH
CH OH
CH3
Glycine (Gly) Alanine (Ala) Valine (Val) Isoleucine (Ile) Leucine (Leu)
Phenylalanine (Phe) Tyrosine (Tyr) Tryptophan (Trp) Methionine (Met) Histidine (His)
Serine (Ser) Threonine (Thr)
CH2
C
NH2
O
CH2
CH2
C
NH2
O
CH2
SH
Cysteine (Cys) Asparagine (Asn) Glutamine (Gln)
HN CH2
C
OH
O
CH2
CH2
C
OH
O
CH2
CH2
CH2
CH2
NH2
CH2
CH2
CH2
NH
C
Proline (Pro) Aspartic Acid (Asp) Glutamic Acid (Glu) Lysine (Lys) Arginine (Arg)
HN NH2
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