100passage-basedOrganicQuestions

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Passage I (Questions 1-4)

Cow’s milk is a nutritionally complete foodsource which contains water, vitamins, minerals,

proteins, carbohydrates, and lipids.

An important protein in milk is casein. Thistypically exists in milk as its calcium salt,calcium caseinate . Calcium caseinate is soluble atthe normal pH of milk (6.6), but it becomes aninsoluble form of casein in solutions that have alower pH of 4.6 (the isoelectric point of calciumcaseinate).

Milk contains two other important types of proteins, which can be denatured and precipitated by heat, namely lactalbumins andlactoglobulins, .

Lactose (shown below), is the maincarbohydrate in milk. It is a disaccharide whichcan be hydrolyzed with acid to give twomonosaccharides, galactose and glucose. In the

body, the enzyme lactase, digests lactose togalactose and glucose.

OH

O

O

OHHO

HO

O

HO

OH

OH

OH

lactose

OH

OH

OH

HO

O

OH

galactose

OH

OH

OH

HO

O

OH

glucose

Lactase

Adding a dilute solution of acetic acid to nonfatmilk is the first step in isolating several of the

components of milk. The solid material that precipitates (Solid 1) is removed. Care must betaken to avoid adding an excess of acetic acid.

The remaining acidic solution is then treatedwith powdered CaCO 3 and heated to boiling,after which time another solid (Solid 2) forms.Solid 2 is removed by filtration, and hot ethanol isadded to the aqueous filtrate. The solution is

allowed to cool overnight, during whichtime lactose crystallizes in the flask.

1. The formation of curds in sour milk ismost likely a result of the precipitationof:

A) casein as the pH decreases.B) casein as the pH increasesC) lactose as the pH decreasesD) lactose as the pH increases

2. In the method described in the passage,the powdered calcium carbonate is

probably used to:

A) neutralize any acetic acid that may be present

B) dissolve any Solid 1 that remainsC) react with calcium caseinate to form

caseinD) increase the solubility of Solid 2 in

the aqueous solution

3. The conversion of lactose to glucose andgalactose involves the net addition tolactose of which of the following?

A) H 3O+

B) O 2 C) H 2OD) H 2

4. The major components of Solid 2 aremost likely:

A) only lactose and caseinB) casein, lactalbumins, and

lactoglobulinsC) lactalbumins and the lactoglobulinsD) lactose, lactalbumins, and

lactoglobulins




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Passage II (Questions 5-9)

Carvone (shown below) can exist as one of twoenantiomers. One of them, (-)-carvone isresponsible for the fragrance of spearmint oiland the other, (+)-carvone, provides thecharacteristic odor in caraway seed oil.

O

carvone

A chemist attempted to isolate (+)-carvone fromcaraway seed oil, which consists almost entirelyof (+)-carvone and limonene (shown below).

limonene

Because the two compounds have different boiling points, vacuum fractional distillation

was chosen as the method of separation . Theapparatus in Figure 1 was assembled, and asample of caraway seed oil was placed in thedistillation flask. A bubbler (or ebuliator) waslowered into the distillation flask to introducesmall air bubbles into the system. Thefractionating column and distillation head werewrapped with glass wool, and the apparatus wasconnected with thick tubing to a vacuum source.

The contents of the distillation flask wereheated, and two fractions were collected inthe receiving flask.

Figure 1 Vacuum distillation apparatus

5. When the caraway seed oil is heated,which of the two components will distillfirst?

A) Limonene, because it has the lower

boiling pointB) (+)-Carvone, because it has thelower boiling point

C) Limonene, because it has the higher boiling point

D) (+)-Carvone, because it has thehigher boiling point

6. The most likely function of the bubbler(ebuliator) is to:

A) provide an outlet when the system

pressure becomes too highB) promote the establishment of a highvacuum in the system

C) prevent superheating of the liquid to be distilled

D) keep the condensed vapors cool inthe receiving flask




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7. Which of the following experimentalmodifications will most likely improve thedegree of separation between limonene and(+)-carvone?

A) Heating the distillation flask at a slowerrate

B) Using a vacuum source that can achieve alower pressure inside the distillationapparatus

C) Cooling the condenser with ice waterD) Using a shorter fractionating column

8. Carvone is shown below with some carbonatoms labeled

O

carvone

12

3 45

67

(+)-Carvone and (–)-carvone differ in theorientations of the substituents around whichof the carbon atoms?

A) Carbons 2, 5, and 7 onlyB) Carbon 5 onlyC) Carbons 2 and 5 onlyD) Carbon 2 only

9. If a leak develops in the vacuum distillationapparatus, the boiling points of the twocomponents of caraway seed oil will:

A) both increaseB) both remain the sameC) both decreaseD) become more similar

Passage III (Questions 10-14)

When Compound 1 is heated with NaOEt,Compounds 2 and 3 are formed

(Reaction 1).

H

Br

NaOC 2H5

heat

Compound 1

Compound 2 (major)

H

OC2H5

Compound 3 (minor)

Two mechanisms were proposed forReaction 1.

Mechanism A

HBr is eliminated from Compound 1 toform a symmetrical vinyl carbene ,Intermediate A, which then rearranges toform Compound 2.

H

Br

OC2H5

Compound 1

Intermediate A

Mechanism B

Ethoxide abstracts a proton from Compound1 to produce a carbanion, Intermediate B.This then rearranges, with loss of bromide,to form Compound 2.




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H

Br

OC2H5

Intermediate B

Br

To distinguish between the 2 mechanisms, an

isotopic labeling experiment was designed. 2compounds (Compounds 4 and 5) were labeledwith carbon-14 ( 14C), and then each was treatedwith potassium t -butoxide (see Scheme 1).Because Compounds 4 and 5 formed varyingratios of Compounds 6 and 7, Mechanism A wasruled out.

*Br

*Br

*

H

Br

Br

+ t-BuO

*

H

Br

Br

+ t-BuO

88%

Compound 6

8%

12%

92%

Compound 4

Compound 5

Compound 7

Scheme 1 (* denotes C14 label)

10. Based on the results of Scheme 1, thechemists most likely ruled outMechanism A because they assumedthat a symmetrical intermediate shouldrearrange to form:

A) Compound 6 onlyB) neither Compound 6 nor

Compound 7C) equal amounts of Compounds 6

and 7D) Compound 7 only

11. Compound 3 most likely is formed as aresult of which of the following types ofreactions?

A) EliminationB) SubstitutionC) CyclizationD) Halogenation

12. Which of the following by-products areformed in Reaction 1

A) NaBr and EtOH

B) Br 2 and NaOEtC) HBr and NaOEtD) EtBr and NaOH

13. Compounds 2 and 6 can bedistinguished from each other by all ofthe following techniques EXCEPT

A) gas-liquid chromatographyB) mass spectrometryC) proton NMRD) specific rotation

14. The transformation of Compound 1 toCompound 2 involves which of thefollowing changes in hybrid orbitals?

A) sp2 to spB) sp2 to sp 3 C) sp3 to sp 2 D) sp to sp 3




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Passage IV (Questions 15-20)

As part of an experiment, a starting materialwas treated with NaOH in acetone solvent((CH 3)2C=O) however, the starting material wasrecovered unreacted. Instead a small amount ofProduct A (shown below) was isolated.

O OH

Product A

It was determined that Product A resulted fromthe aldol self-condensation of acetone.Product A was identified based on the followingobservations.

Observations about Product A

1. Product A had a molecular weight of 116.2. Elemental analysis of Product A showed

only carbon, hydrogen, and oxygen in themolecule.

3. Signals in the infrared spectrum of ProductA included a broad band at 3400 cm -1 and

an intense signal at 1720 cm-1

.4. Product A was a methyl ketone as it gave a positive iodoform test.

5. When Product A was treated with Br 2 inCCl 4, the red bromine colour persisted,

because no carbon-carbon double bondswere present to react with the bromine.

The structure of Product A was furtherconfirmed when treatment with hot sulfuric acidresulted in the corresponding dehydration

product, Product B.

15. What is the molecular weight of acompound that undergoes an aldol self-condensation reaction to result in a β-hydroxy ketone with a molecular weightof 144?

A) 70B) 72C) 74D) 76

16. The aldol self-condensation of acetoneis an equilibrium that favors acetoneover its condensation product. Which ofthe following experimentalmodifications is most likely to shift the

position of equilibrium toward ProductA?

A) Using only a catalytic amountof NaOH

B) Using only a catalytic amountof acetone

C) Removing Product A as it isformed

D) Increasing the reactiontemperature to the boiling pointof acetone




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17. Based ONLY on Observations 1 and 2 only,which of the following compounds could have

been Product A?

A)

B)

O OH

C)

O

D)

OH

OH

18. If a drop of Br 2 in CCl 4 is added to ProductB, the resulting solution will be:

A) colourless, because Product B doesnot contain a carbon-carbon double

bondB) colourless, because Product B

contains a carbon-carbon double bondC) red, because Product B contains a

carbon-carbon double bondD) red, because Product B does not

contain a carbon-carbon double bond

19. A proton NMR spectrum of a sample ofthe isolated Product A was obtained. Ifthe sample were contaminated withacetone, how many extra signalscorresponding to the acetone would be

present in the spectrum?

A) 1B) 5C) 2D) 6

20. Which of the following compoundsfrom the passage will give a positiveiodoform test?

A) Product A only

B) Products A and B onlyC) Product A and acetone onlyD) Products A and B, and acetone




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Passage V (Questions 21-25)

A chemist wishes to make the products shown below by the following synthetic schemes.

A B

C

Lindlar's Catalyst

C5H11Br NaNH2, NH3

HBr, ether

Synthesis 1

Br

D EBr 2

FeBr 3

CH2CH2

H+

KMnO4

COOH

Br

Synthesis 2

21. In synthesis 1 compound A is:

A) EtheneB) EthaneC) But-1-eneD) Acetylide anion

22. In synthesis 1 compound B is:

A) 5-methyl-hept-1-eneB) 5-methyl-hept-1-yneC) 5-methyl-hept-2-eneD) 5-methyl-hept-2-yne

23. In synthesis 1 compound C is:

A) 2-methyl-heptaneB) 5-methyl-hept-1-eneC) 5-methyl-2-bromo-hept-1-eneD) 5-methyl-hept-2-ene

24. In synthesis 2 compound D is:

E) 1,2-dibromobenzeneF) 1,3-dibromobenzeneG) BromobenzeneH) Bromocyclohexane

25. In synthesis 2 compound E is:

A) p-ethylbromobenzeneB) p-methylbromobenzeneC) p-bromobenzaldehydeD) m-ethylbromobenzene

Passage VI (Questions 26 - 29)

Three different methods of preparingalcohols from alkenes are shown below:

H+ / H 2O

OH

Equation 1

Equation 1 shows the acid catalysedhydration of an alkene. The reaction is

regioselective and not stereoselective andrearragements may occur.




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Hg(OAc) 2

H2OOH

OH

HgOAc HgOAc

+

NaBH 4

OH

S ep I

Step II

Equation 2

Equation 2 shows theoxymercuration/demercuration reaction. This is atwo step reaction and the final alcohol is formedvia the oxymercurial alcohols shown after step I.The mercury is then removed in the second step by

NaBH 4 to give the alcohol product. Overall thereaction is regioselective and the first step is also

stereoselective and no molecular rearrangementsoccur.

StepI

THF.BH 3 or B2H6

+

BH2BH2 H2O2 / OH-

OH

OH+

Equation3

StepII

Equation 3 shows a hydroboration reactionfollowed by a second step to remove the boronspecies to give the final alcohol product. Theoverall reaction is regioselective and is alsostereoselective in both steps. Molecularrearrangements do not take place.

26. Why can rearrangements take place inreactions of the type shown in Equation 1?

A) Because the reaction takes place via theformation of a carbocation

B) Because the reaction takes place via theformation of a carbanion

C) Because the reaction takes place via anSN2 reaction

D) Because the reaction takes place via aradical reaction

27. Which of the following experimentalmethods could be used to form thealcohol from the alkene shown in thescheme below?

OH

I Hydroboration followed by a second stepas described in equation 3 aboveII Oxymercuration / demercuration asdescribed in equation 2 aboveIII Acid catalysed hydrolysis as described inequation 1 above

A) I and II onlyB) II and III onlyC) I onlyD) III only

28. Step II in equations 2 and 3 above arerespectively:

A) An oxidation, a reductionB) A reduction, an oxidation

C) A reduction, a reductionD) An oxidation, an oxidation

29. The IR spectra of the alcohols describedin equations 1-3 all display a broad bandat:

A) 1000 cm -1 B) 2500 cm -1 C) 1500 cm -1

D) 3500 cm-1




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Passage VII (Questions 30 - 33)

A chemist was attempting to synthesisecompound B from iodide A using MeOH as thenucleophile but the reaction was unsuccessful.Instead of obtaining the desired product B, anunknown molecule C was obtained. Molecule Cgave 4 signals in the 1H NMR spectrum, onesinglet integrating to 6H atoms, one singletintegrating to 3H atoms, a quartet integrating to2H atoms and a triplet integrating to 3H atoms.C is the product of a reaction mechanisminvolving a molecular rearrangement step.

30. The structure of unknown C is:

OMeA)

B)

OMe

C) OMe

OMe

D)

31. Which of the following alternativereagents (instead of MeOH) wouldmore likely convert iodide A to thedesired product B.

A) Me-O-MeB) MeONaC) MeCOOHD) MeMgBr

32. Given the reaction conditions, andthat you are told that a molecularrearrangement takes place in theabove equation to give unwanted

product C, the most likelymechanism characteristics of thisreaction are:

A) An S N1 reaction involving acarbocation intermediate

B) An S N2 reaction involvinginversion at a carbon centre

C) A carbene intermediateinvolving a methyl shift

D) A radical mechanisminvolving a methyl shift

33. Which of the following statements

are true?

I. An S N2 reaction at a chiralcarbon inverts thestereochemistry of that chiralcentre

II. An S N1 reaction at a chiralcarbon racemises the chiralityof that centre

III. An S N1 reaction at a chiralcarbon does not change thestereochemistry of the centre

A) I aloneB) II and III aloneC) I and II aloneD) III alone




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Passage VIII (Questions 34 - 37)

The rate of the base-induceddehydrohalogenation reaction ofcis -1-bromo-4- tert -butylcyclohexane is

proportional to the concentration of both the bromide and the base, however that of the trans isomer is proportional only to the concentrationof the bromide.

34. What is the structure of cis -1-bromo-4- tert - butylcyclohexane.

C(CH 3)3

Br

Br

C(CH 3)3

C(CH 3)3

Br

Br

C(CH 3)3

A B C D

35. Which of the following mechanisms bestaccounts for the dehydrohalogenationreaction of cis -1-bromo-4- tert -

butylcyclohexane.

A) E2B) E1C) SN1D) SN2

36. Which of the following statements about

eliminations is true?

A) E1 mechanisms are unimolecular innature and E2 mechanisms require a cisconfiguration of the abstracted proton andleaving group.

B) E1 mechanisms involve carbocationintermediates and E2 mechanismsrequire an anti-periplanar arrangementof abstracted proton and leaving group.

C) E1 mechanisms involve carbocationintermediates and E2 reaction rates are

dependent on the concentration of baseonlyD) E1 reaction rates are dependent on the

concentration of base only and E2mechanisms involve radical intermediates

37. Which of the following mechanisms best accounts for thedehydrohalogenation reaction of trans -1-bromo-4- tert -butylcyclohexane.

A) E1B) E2C) S N2D) Radical




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Passage IX (Questions 38 - 42)

Chemists investigating the antibiotic agent, penicillin G, wished to prepare a number ofanalogues which might solve the problem of

bacterial resistance to this class of drugs. Amethod of production was required which wasefficient and cheap. Chemists decided to startfrom 6-APA and following the scheme outlinedin Reaction 1, they synthesized a number ofanalogues with a variety of groups at R.

N

SMe

Me

HH

H2N

O

CO2H

6-aminopenicillanicacid(6-APA)

R Cl

O

N

SMe

Me

HH

N

O

CO2H

H

O

R

Penicillinanalogues

Reaction1

In order to obtain large enough amounts of6-APA for this synthetic scheme, chemists usedPenicillin G in an enzymatic cleavage reaction toform 6-APA (reaction 2).

N

SMe

Me

HH

N

O

CO2H

H

O

Penicillin G

Penicillin acylase

Hydrolysis

6-APA

Reaction 2

38. In reaction 1, the compound above thereaction arrow is called an acyl chlorideor an acid chloride. From thefollowing list of syntheses of acidchlorides, select from A,B,C or D theanswer which is true.

I A carboxylic acid plus sodiumchloride gives an acid chloride

II A carboxylic acid plus thionylchloride gives an acid chloride

III A ketone plus lithium aluminiumhydride gives an acid chloride

IV An aldehyde plus carbontetrachloride gives an acid chloride

A) I and IIB) I, II and IV

C) II aloneD) IV alone

39. Acid chlorides are useful compounds inchemical syntheses. Which of thefollowing reactions can use acidchlorides as an integral step

I Friedel Crafts acylationII Friedel Crafts alkylationIII Synthesis of esters from alcohols

IV Synthesis of amides from amines

E) I and IIF) I, III and IVG) I and IIIH) IV alone




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40. In reaction 2, the enzymatic hydrolysis ofPenicillin G most likely gives 6-APA andwhat other compound as products?

N

H

O

H

N

O

H

OH

OH

O

H

O

A B

C D

41. Amide bonds are biologically important insuch structures as peptides where they are alsotermed peptide bonds. When chemists wantto synthesise peptides in the laboratory fromtwo different amino acids one of the methodsthat can be used for small peptides utilizesvarious protecting groups and couplingreagents. Which of the following would be anacceptable route for the synthesis of adipeptide by this method.

A) Protect the free amino group of one

amino acid, protect the free carboxylicacid group of the other amino acid, formthe peptide bond with DCC and thendeprotect the amino group and thecarboxylic acid group.

B) Protect the free amino group of oneamino acid, form the peptide bond withDCC, deprotect the amino group

C) Protect the free amino group of oneamino acid, protect the free carboxylicgroup of the other amino acid, form the

peptide bond with DCC.

D) Protect the amino group which will formthe peptide bond of one of the aminoacids, protect the carboxylic acid groupwhich will form the other part of the

peptide bond of the other amino acid, formthe peptide bond with DCC, deprotect theamino group and the carboxylic acidgroup

42. If we did not use protecting groups inthe synthesis of a dipeptide starting fromtwo different amino acids, and insteadused an acid chloride reaction with anamine to form the amide bonds of thedipeptide, how many different productswould we obtain?

A) 1B) 2C) 3D) 4

Passage X (Questions 43 - 47)

Salbutamol is an important molecule usedfor the treatment of asthma. It is a β2agonist and relaxes bronchial smooth muscleresulting in dilation of the airways. In thelaboratory Salbutamol can be synthesizedaccording to the reactions shown inScheme 1.

O

OH

HO

CH3

O

MeOH, HClO

OMe

HO

CH3

O

Br 2

Bromination

O

OMe

HO

CH2

O

Br

PhCH2 NHtBu

O

OMe

HO

CH2

O

NPhH2C

tBu

HO

HO

CH2

OH

NPhH2C

tBu

HO

HO

CH2

OH

HNtBu

H2 Pd/C

LiAlH4THF

Sal uta ol

I

II

III

IV

VVI

Scheme 1




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43. The reaction from molecule I to molecule II inScheme 1 is:

A) An acid catalyzed hydrolysisB) A base catalyzed dehydrationC) An acid catalyzed formation of an etherD) An acid catalyzed esterification

44. The transformation of molecule III tomolecule IV in Scheme 1 is an example of:

A) An E1 reactionB) An S N1 reactionC) An E2 reactionD) An S N2 reaction

45. The transformation from molecule IV tomolecule V in Scheme 1 is what kind ofreaction?

A) A hydrolysisB) A reductionC) A rearrangementD) A de-esterification

46. If the chemist had used LiAlD 4 as thereagent in the transformation of molecule IV

to molecule V instead of LiAlH 4 what wouldhave been the product?

DO

HO

CH2

OD

NPhH2C

tBu

HO

HO

CH2

OH

NPhH2C

tBu

HO

HO

CH2

OH

NPhH2C

tBu

DO

HO

CH2

OD

NPhH2C

tBu

H D

DHD D DD

H H D D

A B

C D

47. In the last step of the synthesis ofSalbutamol shown in Scheme 1, thePd/C is acting as a:

A) ReagentB) CatalystC) Radical initiatorD) Drying agent

Passage XI (Questions 48 - 52)

Non steroidal anti-inflammatory agents(NSAIDs) are a successful class ofcompounds used for the treatment of painand inflammation in a range of disorders andare especially useful in the treatment ofarthritis. One such drug is Ibuprofen. In the

laboratory chemists can prepare the racemicibuprofen compound by many differentroutes. One such synthetic route is shown inScheme 1 below.

Cl

O

AlCl 3 O

NaBH4

OHH

PBr 3

Br H

NaCN

CNH

H+ / H2Oheat

CO2HH

I II

IIIIV

V VI Ibuprofen

Sche e 1

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