Chemistry 223b Midterm Test - Western Universityinstruct.uwo.ca/chemistry/2223/downloads/2008midterm-blank.pdf · Chemistry 223b Midterm Test Saturday, ... Please ensure that you

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)


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


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


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


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


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


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'


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


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


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


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


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%)


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.


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


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


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


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


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


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


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


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)


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)


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


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


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- 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

Scrap paper

Scrap paper

Scrap paper

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Chemistry 223b Midterm Test - Western Universityinstruct.uwo.ca/chemistry/2223/downloads/2008midterm-blank.pdf · Chemistry 223b Midterm Test Saturday, ... Please ensure that you