Princeton WB OChem

Which of the following radical reactions is an example of a free-radical chain propagation step.. Which of the following radical reactions is an example of a free-radical chain terminati

MCAT SciENCE WoRKBOOK

MCAT Biological Sciences Review

MCAT Biology Chapter Title

Molecular Biology

Microbiology

Generalized Eukaryotic Cells

Genetics and Evolution

Nervous and Endocrine Systems

Circulatory, Lymphatic, and Immune Systems

Digestive and Excretory Systems

Muscle and Skeletal Systems

Respiratory and Skin Systems

Reproductive Systems and Development

MCAT Physical Sciences Review

MCAT Physics Chapter Title

Electricity and Magnetism

Oscillations and Waves

MCAT Physical Sciences Review

MCAT General Chemistry Chapter Title

33,56,62, 63,64, 65,66 8,9, 15,22,38,39,58,59,67-74 40,42,43,44,45, 46,47,61, 75 14,57, 76, 77,78

41,48,49,50,51,60, 79 52,53,54, 80

1 Q-13, 19-24 31,32 25-30,33-39 14,40,45,46,48-55 42,43,56,57 41,44,47,58-60

Corresponding MCAT Sqience Workbook Passage Numbers

1-4,6,9-18,70

5, 7,19-28,43,72 35,57,59, 60,62, 63,65,66 40,61,64, 67

31,41, 42, 45,68, 69 33,44, 71

29,37,39,46

PERIODIC TABLE OF THE ELEMENTS

MCAT

ORGANIC CHEMISTRY

PRACTICE QUESTIONS AND pASSAGES

Questions 1 through 33 are NOT based on a

descriptive passage

1 Identify the hybriziations of the two indicated carbon

atoms in the following molecule

4 What is the degree of unsaturation for a molecule with

the molecular formula C 14H12?

A 6

B 9

c 12

D 18

5 Rank the average C-0 bond length from shortest to

longest for CO, C02 and C03-

9 Optically-active compounds that rotate plane-polarized

light in the clockwise direction are designated:

A (R)

B (S)

c dextrorotatory

D levorotatory

10 (R)-Glyceraldehyde has an optical rotation of [a]~=

+13.5° The optical rotation of a 50:50 mixture of

(H)-glyceraldehyde and (S)-glyceraldehyde:

13 Which of the following molecules contains an (R)

15 Which of the following molecules does NOT contain an

internal plane of symmetry?

18 Each of the following statements about diastereomers

is true EXCEPT:

A they may have different melting points

B they may have different retention times on a gas

chromatogram

C they may have different molecular formulas

D they may have different optical rotations

19 Which of the following is a meso compound?

20 The tosylate group,

D its higher nucleophilicity

21 Which of the following represent possible resonance contributors to the structure of the conjugate base of trifluoromethanesulfonic acid?

22 Of the following, which is the strongest acid?

27 Which of the following is a valid resonance form of the

28 Which of the following orbitals is NOT found in the

carbon-carbon bonds of propene?

Passage 1 (Questions 1·5)

Recent research has demonstrated that there is a class of

DNA-cleaving molecules that are referred to as enediynes

These compounds are known as enediynes because they

contain a continuous six-carbon unit in which there is one

double bond and two triple bonds These DNA-cleaving

molecules appear to be quite potent and, most importantly,

selective in regards to anticancer activity The following

molecule has proven to be one of the more potent of these

enediyne molecules:

1 Give the hybridization of the carbon atom and the

oxygen atom indicated by the arrows

A The carbon is not chiral

B The carbon has an R absolute configuration

C The carbon has an S absolute configuration

D The absolute configuration at this carbon cannot

Passage 2 (Questions 1·6)

A research chemist synthesized Compound A, which was

shown to be a powerful analgesic upon clinical testing

Further evidence indicated only one stereoisomer of A was

the active agent The researcher was instructed to separate

Compound A into its different stereo isomers to help determine

which one was the analgesic

Compound A, which showed an optical rotation of 0°,

was treated with the R stereoisomer of Compound B (melting

point 55°C) Two easily separated solids, C and D, whose

melting points were 101 °C and 90°C, respectively, were

isolated from the reaction mixture Compounds C and D

were then independently treated with warm aqueous acid

After workup, Compound C gave Compounds E and B, while

Compound D yielded F and B Testing of Compounds E and

F determined that E was the active analgesic, while F was

biologically inactive

1 Compound A could be described as:

A a meso compound

B a racemic mixture

C an equal mixture of two diastereomers

D an optically pure compound

2 If the melting point of Compound E is 80°C, what

should be the melting point of Compound F?

4 The absolute configuration of E was determined to be

R Compound E also showed a positive optical rotation

The configuration and optical rotation of Compound F

S Reaction of Compound A with Racemic B would give how many stereoisomers?

Passage 3 (Questions 1 -7)

Disparlure, cis-1 ,8-epoxy-2-methyloctadecane, is a

pheromone of the gypsy moth Porthetria dispar Synthetic

disparlure has proven to be a potent agent for attracting and

trapping this harmful pest [t is important to note that the

presence of the enantiomer in a sample of natural pheromone

dramatically reduces the compound's activity For this

reason, the synthetic preparation of enantiomerically pure

disparlure is essential

Dis par lure

1 In disparlure, what are the absolute configurations of

D Cannot be determined from the information given

4 Disparlure and the molecule shown below can best be

S In the molecule below, both side chains of disparlure

have been replaced with hexyl groups Which of the following is true about this molecule?

A It is meso

B Its absolute configuration is 1R, SR

C Its absolute configuration is 7 S, 8R

D Its absolute configuration is 7S, 8S

6 If disparlure is treated with H• and H20 to open the

epoxide ring, what product(s) will be formed?

7 In which of the following solvents should disparlure be

Questions 1 through 28 are NOT based on a

2 The most stable conformational isomer of

methyl-cyclohexane is a chair form with the methyl group:

A gauche

B equatorial

C axial

D planar

3 For which of the following compounds will hydrogen

bonding among its molecules be important?

I

A II only

B III only

C I and II only

D II and III only

4 Which one of the following molecules would correctly

be called a cis-disubstituted cycloheptane?

A

0

D

S Which of the following intermediates is most likely

involved in this reaction?

9 Which one of the following molecules will most easily

10 Which of the following best represents the highest

energy species on an SN2 reaction coordinate diagram?

14 Rank these three carbocations in order of increasing

15 In an E2 reaction, all of the following occur in the

rate-determining step EXCEPT:

)l departure of the leaving group

B rehybridization of the two reacting carbon centers

17 2-Cbloro-2-methylbutane more readily undergoes SNl

type reactions than SN2 reactions when in the presence

of sodium alkoxide If the concentration of the

nucleophile is increased, then the:

A rate of reaction increases

B rate of reaction decreases

C rate of reaction does not change

D SN2 reaction predominates

MCAT SCIENCE WORKBOOK

18 Which of the following radicals is the most stable?

19 Which of the following radical reactions is an example

of a free-radical chain propagation step?

20 Which of the following radical reactions is an example

of a free-radical chain termination step?

22 Which of the following intermediates is most likely

involved in this reaction?

MCAT SciENCE WoRKBOOK

23 What is the major product of this reaction?

24 What is the major product of this reaction?

A destabilizes the nucleophile

Passage 4 (Questions 1-6)

Table 1 lists many of the substitution reactions that alkyl

halides undergo in the presence of nucleophilic reagents

1 Ethers can be formed from methyl chloride in Reaction

Type V In this reaction, the incoming OR'- group

2 A certain alkyl halide forms a carbocation that is more

stable than the carbocation formed from isopropyl

bromide What is the most likely formula name of the

B an SNI reaction to produce a secondary alkyl halide

C an oxidation reaction to form a carboxylic acid

D an elimination reaction to form an alkene

4 A substitution reaction involving methyl iodide would most likely demonstrate which of the following?

A Carbocation formation and optical activity

B A unimolecular rate-determining step

C Racemization and first-order kinetics

D Second-order kinetics

S A quaternary ammonium salt does NOT carry out substitution reactions with alkyl halides because the nitrogen atom is:

A acetate

B carbocation intermediate

C configu·ration inversion

D intermediate racemates

Passage 5 (Questions 1-6}

When an organic compound is burned completely in

oxygen, the energy released is known as the heat of

combustion For simple hydrocarbons, the general formula

is given by the following equation:

The heat of combustion of a particular compound depends

on several factors, including molecular weight, angle strain,

and degree of branching In most cases, the compound with

the higher molecular weight will have the larger heat of

combustion For simple alkanes and cycloalkanes, each

additional -CH2- adds approximately -156 kcal/mol to the

heat of combustion For cycloalkanes, this value increases

with increasing angle strain

More meaningful information can be obtained by

comparing the !J Heomb of several isomeric compounds This

allows chemists to determine which structural features are

the most thermodynamically stable Research has shown

that straight-chain hydrocarbons have heats of combustion

of greater magnitude than those of more branched isomers

In addition, molecules that have little or no angle strain tend

to have lower heats of combustion than compounds with

bond angles that substantially deviate from the normal value

for that bond type, for example approximately 109° for an

sp 3 hybridized carbon atom

1 The heat of combustion of propane is reported to be

-530 kcal/mol A reasonable approximation for the

heat of combustion for n-heptane would be:

A -685 kcallmol

B -840 kcal/mol

C -995 kcal/mol

D -1150 kcal/mol

2 The complete combustion of one mole of neopentane in

3 Which one of the following molecules would have the heat of combustion of highest magnitude (i.e., most negative)?

A.~ c

4 The heat of combustion of n-hexane is -995 kcal/mol, while the heat of combustion of 2-methylpentane is

-994 kcallmol One can therefore conclude that:

A n-hexane has greater angle strain than pentane

2-methyl-B 2-methylpentane is more branched than n-hexane

C 2-methylpentane is thermodynamically less stable than n-hexane

D n-hexane has a lower molecular weight

S A planar ten-membered ring would have bond angles of

144° Cyclodecane has a heat of combustion of

-1574 kcal/mol, suggesting very little angle strain One might conclude from this information that:

A cyclodecane is not a planar molecule

B bond angles larger than 109° do not increase angle strain

C the carbon atoms in cyclodecane are sp 2

hybridized

D n-decane would have the same heat of combustion

6 The difference in the heats of combustion of cyclohexane and cycloheptane is due mainly to the difference in:

A angle strain

Passage 6 (Questions 1·5)

Free radical bromination of alkanes proceeds by the

following chain reaction mechanism:

Br· + R-H ~ HBr + R· (2)

Since the order of radical stability is 3° > 2° > 1°,

bromination occurs preferentially at the most substituted

position, although all possible regioisomers are usually

formed A typical reaction is shown below:

When reacting with alkenes, bromine radicals tend to add

to the least substituted carbon of the double bond, the reverse

of the ease with alkanes

1 How many different monobrominated compounds would

be produced by the free radical bromination of

2 Step 1 of the radical chain reaction mechanism for the bromination of alkanes would be described as:

A fractional distillation

B crystallization

C extraction

D thin-layer chromatography

4 The major product from the radical addition of bromine

to 1-butene would be:

A 2, 2

B 2, 3

c 3, 2

D 3,3

passage 7 (Questions 1-7)

Alkyl halides are of great importance in laboratory

synthesis They undergo displacement reactions with

nucleophilic reagents to yield products such as ethers,

alcohols, and amines In reactions, alkyl halides may follow

second-order kinetics The general reaction involving

nucleophilic substitution is shown below:

R-X + :Y- solvent R-Y +

:x-substrate nucleophile leaving

group

SN2 reactions are influenced by the structure of the alkyl

substrate, the type of solvent and the nature of the nucleophilic

reagent The rate of nucleophilic substitution reactions is

dependent upon the concentration of the substrate and of the

nucleophile as expressed below:

Rate = k[R-X][Y]

where k is the reaction rate constant Thus, both reactants are

involved in the rate-determining step of the reaction

3CCH2 3.3 x ro-7

H2C=CHCH2 1.3

C6H5CH2 4.0

I

Table 1 Average Relative SN2 Rates of Alkyl Groups

2 The n-pentyl group has the structure shown below:

It will have a reaction rate that is closest to which of the following alkyl groups from Table 1?

A first-order rate of reaction

B complete inversion of stereochemistry

C reactivity sequence of 1° > 2° > 3°

D absence of rearrangement

4 If the concentrations of both CH3Br and OH-are doubled

in a substitution reaction resulting in the formation of

CH30H and Br- then the rate of the reaction will:

A only the SNl rate depends upon the solvent

B only the SNl rate depends upon the temperature

C the SNl rate depends only upon the concentration

Passage 8 (Questions 1-6)

When most alcohols are heated with H2SO4 they dehydrate

and form an alkene; the more substituted the alcohol, the

faster the elimination This dehydration usua.lly proceeds

through a carbocation which may rearrange before losing a

proton to form the alkene Typically, the more substituted

alkene is formed due to its greater stability In most cases,

mixtures of alkenes will result if more than one product is

possible An energy diagram for the dehydration of tertiary

Alcohol A is shown below

-l Alcohol Y was dehydrated and gave three isomeric

products Which of the following methods would be

the best to use in determining the structures of the three

C T.he less stable alkene product

D The protonated starting alcohol

3 For the conversion of A to C, the energy of activation

would be represented by:

A position of A to 2

B position of A to C

C position of B to C

D position of A to 1

4 Which of the following statements about the energy diagram is true?

A Conversion of B to C would have a higher rate constant than C to D

B Conversion of E to C would have a higher rate constant than D to C

C Conversion of A to B would have a higher rate constant than D to E

D Position C is more thermodynamically stable than position B

Passage 9 {Questions 1-5)

Camphor is a naturally-occurring, chira!, bicyclic ketone

It has a distinctive pine odor and is used in many medicines

and health aids

Camphor

1

When camphor is treated with MeMgBr, two isomeric

compounds are formed: E and F Compounds E and F were

individually reacted with concentrated HBr and both produced

isomeric bromides S and T

1 What is the maximum possible number of stereoisomers

A They are diastereomers

B They are enantiomers

C They are identical stereoisomers

D They are meso isomers

3 What are the absolute configurations of carbons 1 and

2 (see figure), respectively, in the camphor molecule?

4 The specific optical rotation of Bromide S was measured

to be +52° What would be the specific optical rotation

of Bromide Tl

A -52°

B 0°

c +52°

D Cannot be determined from the information given

S Treatment of Compound T with Nai in ethanol would

proceed by:

A SNl and give one product

B SNl and give two products

C SN2 and give one product

D SN2 and give two products

Passage 1 0 (Questions 1·6)

A student ran a series of experiments to study the SNl and

SN2 reaction mechanisms The results are shown below:

1 In Reaction 4, the (R)-2-bromopentane had an optical

rotation of -82.6° The rotation of the product would

be which of the following?

A -82.6°

c +82.6°

D Cannot be determined

2 If the volume of acetone in Reaction 1 were doubled,

then the reaction rate would:

A decrease to one-fourth the original rate

B decrease to one-half the original rate

C remain the same

D increase to twice the original rate

3 Which of the reactions proceeded predominantly by the SNl substitution mechanism?

B It proceeds with retention of stereochemistry

C It proceeds best with primary alkyl halides and is

A 2-Methyl-2-hexene

B 3-Methyl-2-hexene

C (R)-3-Methoxy-3-methylhexane

D Racemic 3-methoxy-3-methylhexane

2 The acid-catalyzed addition of water across the C=C

double bond of propene is characterized by all of the

following EXCEPT:

A carbocation formation

B the first step in the mechanism involves protonation

of the C=C double bond

C alcohol product formation

D anti-Markovnikov regiochemistry

3 The mechanism for addition of H-Cl across a C =C

double bond involves:

A proceeds by a concerted pathway

6 In electrophilic aromatic substitution reactions, typically an extremely reactive electrophile is used because the aromatic ring is:

A very reactive

B a very poor nucleophile

C a very poor electrophile

B I< II< III

c II< I< III

9 What is the major product of thls reaction?

10 What is the major product of this reaction?

11 What is the major product of this reaction? 13 What is the major product of this reaction?

14 What is the major product of this reaction?

16 What is the major product of this reaction?

17 What is the major product of this reaction? 18 What is the major product of this reaction?

19 What is the major product of this reaction? 20 What is the major product of this reaction?

21 What is the major product of this reaction?

23 Which of the following substituents increases the acidity

of a substituted phenol as compared to the unsubstituted form?

Passage 11 (Questions 1·9)

Dienes, a special group of alkenes, can be classified as

conjugated or isolated Conjugated dienes are alkenes with

alternating double and single bonds Isolated dienes have

double bonds separated by more than one single bond

conjugated diene isolated diene

Although conjugated dienes are similar in reactivity to

isolated dienes, conjugated dienes are somewhat more stable

The heats of hydrogenation were measured for several alkenes

and dienes to determine their stability (Table 1) The data

show that alkenes become more stable with increasing

substitution and increasing number of double bonds

For example, in Table 1 the 6.Hh y d rog of 1 ,4-pentadiene, an

isolated diene, is 60.8 kcal!mol, approximately double the

ll.Hh d of 1-butene However, 1,3-butadiene has a 6.Hh d

y rog y rog

of 57.1 kcal/mol Based on these results, conjugated dienes

are considered more stable because they release less heat on

Table 1 Heats of Hydrogenation of Alkenes

One explanation for this observation is the hybridization ·~

theory According to the hybridization theory, the stability

of conjugated dienes comes from the hybridization of the orbitals forming the carbon-carbon single bonds

For example, in 1 ,4-pentadiene, the C-C single bonds result from the overlap of an sp 2 orbital from one carbon with

an sp 3 orbital from the adjacent carbon In conjugated dienes, on the other hand, the c-,c single bonds result from

cr overlap of sp 2 orbitals on both carbons

1 In a manner similar to other alkenes, conjugated dienes typically undergo electrophilic addition Which of the following most accurately represents the reaction intermediate formed when 1,3-butadiene reacts with HCl?

o+ o+

A H2C=-=-=CH:-::-:CH-~CH3

o+ o+

B H3C-CH:·::-::CH=-::-:CH2 o+ o+

C H3C-.:.-CH CH=-::-:CH2

2 The carbon-carbon single bond in 1,3-butadiene has a bond length that is shorter than a carbon-carbon single bond in an alkane This is a result of the:

A overlap of two sp 2 orbitals

B partial double-bond character due to the a

electrons

C overlap of one sp 2 a:nd one sp 3 orbital

D overlap of two sp 3 orbitals

3 In comparison to a normal alkane bond, the C(2)-C(3) bond in 1,3-butadiene has:

A more s character

B less s character

C more p character

D less energy

4 What is the IUPAC name of the major product that is

formed when 1,3-butadiene is reacted with an equal amount of HCl?

A 1-Chloro-2-butadiene

B 3 -Chlora-l-butadiene

C 1-Chloro-2-butene

D 3-Chloro-1-butene

5 If one mole of 1,3·butadiene is completely

hydrogenated, what is the expected amount of heat

6 Treatment of 2-methyl-1,3-butadiene with one

equivalent of HCl might give rise to all of the following

7 Monoalkenes have carbon-carbon double bonds

consisting of a a bond and a 1t bond The carbon atoms

are sp 2 hybridized and have:

A two equivalent orbitals and one \lnhybridized p

D four equivalent orbitals in a hybridized state

8 If an unsymmetrically-substituted alkene is used in an

electrophilic addition reaction, a single addition product

is usually formed, rather than a mixture of products In

the addition ofHX to an alkene, the acidic proton would

become attached:

Passage 12 (Questions 1-7)

The hydrogenation of alkenes in the presence of a suitable catalyst produces alkanes The heat of hydrogenation is the amount of heat released when molecular hydrogen is added

to the double bond These exothermic processes are represented by the reaction of ethylene with hydrogen in Reaction 1:

Pd/C Reaction 1

The table below lists the heats of hydrogenation for a number of unsaturated hydrocarbons

Alkene All hydrog (kcal/ mol)

Table 1

Alkenes can also undergo oxidation Ozone, a powerful oxidizing agent, re~cts q~ickly with alkenes by cleaving the double bond to produce two molecules (Figure 1 ) The oxidation reaction occurs via Intermediates 1 and 2

CHzCh, -78 "C

0 o/ 'o

[ ~>(O)( l CH,m~HIHzO

An ozonide

Intermediate 2

Figure 1

1 When 1-butanol is dehydrated, the new compound's

beat of hydrogenation is most likely:

A less than 27 kcal/mol

B between 27 and 30 kcallmol

C between 30 and 33 kcal/mol

D greater than 33 kcallmol

2 Heptylamine is deaminated via the diazonium salt, and

the product is dehydrogenated to yield 1-heptene:

The beat of hydrogenation of 1-heptene should be closest

to the heat of hydrogenation of which one of the

B is more highly unsaturated

C has steric strain between the 2 bulky substituents

D shows no stereospecificity

4 Can cis2butene be converted easily to trans2butene?

-A No, because bond rotations cannot occur under·· mild conditions

B Yes because of the hybridized orbitals

C No, because the double bonds differ in spatial arrangement

D Yes, because the two alkenes differ in heats of hydrogenation

5 Which of the following is most likely the structure of Compound X?

hydro-A is stereospecific

B has a positive beat of formation

C requires a much greater energy of activation

D releases more energy than does hydrogenation of

cis-2-butene

7 According to the mechanism shown in Figure 1, what is the hybridization of C-1 in the alkene, molozonide, ozonide, and carbonyl product, respectively?

A sp3; sp2; sp; spl

B spl; sp3; sp3; spl

c sp2; spl; sp3; sp3

D sp3; spl; spl; sp3

The mechanism of this reaction is such that equal amounts

of each product are formed The reaction mechanism proceeds

via a planar intermediate which can be attacked by an iodide

ion on either side of the plane to yield equal amounts of ( +)

2 (-)-2-Iodopentane's absolute configuration is - - - •

and (+)-2-iodopentane's absolute configuration is

4 The hybridization of the carbon of the carbocation intermediate can be best described as:

A The slow step of the reaction is the formation of the intermediate carbocation

B The overall rate of the reaction depends on the concentrations of both 1-pentene and hydrogen iodide

C The products form a racemic mixture

D (+)-and (-)-2-Iodopentane have different boiling points