Organic chemistry section test (1)

Sulfanilic acid, illustrated below, can be recrystallized from hot water and has an extremely high melting point 288oC relative to its molecular weight 173.2.. Which of the following dep

Trang 1

MCAT Subject Tests

Dear Future Doctor,

The following Subject Test and explanations contains questions not in test format and should be used to practice and to assess your mastery of the foundation content necessary for success on the MCAT Simply memorizing facts is not sufficient to achieve high scores; however, an incomplete understanding of basic science knowledge will limit your ability to think critically Think of building your content knowledge as learning the vocabulary and practicing MCAT-like questions as actually speaking

All rights are reserved pursuant to the copyright laws and the contract clause in your enrollment agreement and as printed below Misdemeanor and felony infractions can severely limit your ability to be accepted to a medical program and a conviction can result in the removal of a medical license We offer this material for your practice in your own home as a courtesy and privilege Practice today so that you can perform on test day; this material was designed to give you every advantage on the MCAT and we wish you the best of luck in your preparation

Sincerely,

Albert Chen

Executive Director, Pre-Health Research and Development

Kaplan Test Prep

or mechanical without the written permission of Kaplan, Inc This book may not be duplicated,

distributed or resold, pursuant to the terms of your Kaplan Enrollment Agreement

Trang 2

O R G A N I C CH E M I S T R Y SU B J E C T TE S T1

Organic Chemistry Subject Test 1

1 The least stable free radical is

A

C

H

B

CH

3

C

H C 3

H

C

H 3

E

(Φ = phenyl group)

A Φ3C:–

B Φ2HC:–

C ΦH2C:–

E (CH3)3C:–

expected to make the LEAST contribution to the actual hybrid?

A

B

C

D

E All of the above would make an equal contribution

to the hybrid

B CH3CH2CH2OH

C

CH3 CCH 3

O

D H2C=CHCH3

E CH3OCH2CH3

hydrogenation per mole of H2 absorbed?

A 1,3-pentadiene

B 1,4-pentadiene

C 1,2-pentadiene

D 1,3,5-hexatriene

E 1,2,4-hexatriene

K A P L A N _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1

Trang 3

OR G A N I C CH E M I S T R Y SU B J E C T TE S T 1

depicted below, reacts with I– in an aprotic solvent,

second order kinetics is observed Which of the

following statements must be true?

H

C H 2 C H 3

B r

H

A The reactant has R stereochemistry while the

product has S stereochemistry

B The reactant has S stereochemistry while the

product has R stereochemistry

C Both reactant and product have the same R/S

designation

D The product is a racemic mixture of R and S

enantiomers

E The product is optically inactive

A

NH2

CH3

B

N(CH3 ) 2

O

C

N

H

D N(CH3)3

E

CH3

NO2

8 Sulfanilic acid, illustrated below, can be recrystallized from hot water and has an extremely high melting point (288oC) relative to its molecular weight (173.2)

SO3 H

H 2 N The best explanation for the physical properties mentioned is that

A the amino group of sulfanilic acid acts as a Lewis acid

B sulfanilic acid exists as a pair of enantiomers

C sulfanilic acid exists as a pair of diastereomers

D sulfanilic acid exists as a zwitterion

E the sulfur atom of sulfanilic acid has an unusually low oxidation number

A n-butane

B isobutane

C cis-2-butene

D 1-butyne

E 2-butanol

10 Which of the following has the highest boiling point?

A CH3(CH2)2CH3

B (CH3)2CHCH2CH3

C CH3(CH2)3CH3

D (CH3)2CHCH3

E CH3CH2CH3

11 Which of the following has the highest melting point?

A trans-2-butene

B cis-2-butene

C n-butane

D 1-propanol

E 1-pentanol

Trang 4

12 Which of the structures pictured below corresponds to

2-methoxy-3-butenal?

A

O

C

O

CH3

B

OCH 3

C H

O

C

OCH 3

C

O

CH3

D

H

OCH 3

O

H

E

OCH 3

O

13 Which of the following statements is true regarding the

relative boiling points of cis- and trans-

1,2-dichloroethene?

A The boiling point of the cis isomer is higher because

it has a net dipole moment

B The boiling point of the cis isomer is higher because

it is thermodynamically more stable

C The boiling point of the trans isomer is higher

because the _ electrons are more delocalized

D The boiling point of the trans isomer is higher

because it is more symmetrical

E The boiling point of the two will be equal because

cis and trans isomers have identical physical

properties

14

H OH

H OH CHO

CHO

H OH

CHO

CHO The two molecules pictured above are

A meso structures

B enantiomers

C diastereomers

D identical

E racemates

15 Which of the following will be least reactive towards

SN1 substitution?

A

H C Br

H

B

CH3

H

C

CH3

D

CH2 CH3

H

E

H

H Br

Trang 5

16 Which of the following is true regarding SN1 and

SN2 reactions?

A SN1 reactions proceed via a carbocation

intermediate; SN2 reactions do so under certain

conditions

B Both SN1 and SN2 reactions can yield

rearrangement products

C SN1 reactions proceed more readily with a tertiary

alkyl halide as reactant; SN2 reactions proceed more

readily with a primary alkyl halide as reactant

D The rates of SN1 reactions are largely affected by

steric factors; the rates of SN2 reactions are largely

affected by electronic factors

E Protic solvents favor SN2 over SN1 reactions

17 Which of the compounds below has the highest melting

point?

E

D

C

B CHCH3 3 (CH (CH 2 2 ) ) 4 4 COOHCH3

CH2 =CH(CH2 ) 3 CH3

CH3 (CH 2 ) 4 CH2 OH

CH3 (CH 2 ) 2 CH2 OH

A

18 Which of the structures below corresponds to

3-cyano-2-butenoyl chloride?

A

C

N

C

O Cl

B

O Cl

C

H

N

C

H

C O

O

CH2 Cl

N

D

H

C

C N

CH2 Cl

E

O Cl

C

N

H

19 Which of the following statements is true about the compounds pictured below?

CH3 Cl

H

CH2 CH3 Cl

H

CH3

H Cl

CH2 CH3

H Cl

A They are diastereomers with different melting points

B They are diastereomers with identical boiling points

C They are enantiomers with different melting points

D They are enantiomers which rotate plane-polarized light in different directions

E They are identical meso structures

20 Which of the following statements is true about the compounds pictured below?

CH3 Br Br

CH3

H

CH3

H

CH3 Br Br

A They are enantiomers and are optically active

B They are diastereomers and are optically active

C They are diastereomers and are optically inactive

D They are meso structures and are optically active

E They are meso structures and are optically inactive

Trang 6

21 What is(are) the major organic product(s) of the SN1

reaction below?

CH2 CH3

CH3

H +

A

CH2 CH3

CH3

B

H OH

CH2 CH3

CH3

C

CH2 CH3

CH3

CH2 CH3

CH3

D

CH2 CH3

CH3

E

CH2 CH3

CH3

CH2 CH3

CH3

22 Which of the compounds below is an acid anhydride?

A

O

B

O OH

C

OH

D

CH3 CH2 C

O OCH 3

E

O

23 Which of the following compounds will have the lowest boiling point?

A CH3CH2CH2NH2

C

CH3 CHCH3

NH2

E N(CH3)3

24 Which one of the compounds below is incapable of significant hydrogen bonding?

A ethanol

B bromoethane

D propanamide

E ethanamine

Trang 7

25 Which of the following statements is true of ethene?

A Both carbon atoms are sp2 hybridized and the

molecule is planar

B Both carbon atoms are sp2 hybridized and all bond

angles are approximately 109.5°

C One carbon atom is sp hybridized while the other is

sp2

D Both carbon atoms are sp3 hybridized and all bond

angles are approximately 109.5°

E Both carbon atoms are sp hybridized and the

molecule is planar

26 Which of the following depicts the most stable

resonance structure of diazomethane?

A

H C N

H

:

N

B

H C N

H

N

:

C

H C N

H

N

:

D

H C N

H

N

:

E They are all equally stable

27 The compounds pictured below are

CH3

H Br

CH3

H Br

A B

A enantiomers

B meso compounds

C diastereomers

D conformers

28 The IUPAC name for the compound below is

CH3 CH2 CHCH2 CH2 CCH 3

CH2 CH3 CH3

CH3

A 2,2-dimethyl-5-ethylheptane

B 5-ethyl-2,2-dimethylheptane

C 3-ethyl-6,6-dimethylheptane

D 6,6-dimethyl-3-ethylheptane

E Two of the above

29 Which of the following substrates is least reactive towards SN2 reactions?

A CH3I

B CH3CH2Br

C CH3CH2CH2I

D (CH3)2CHCH2I

E (CH3)2CHCH2Br

Trang 8

30 All of the following represent

cis-1,4-dimethylcyclohexane EXCEPT

A

H 3 C

H

CH3

B

CH3

H

C

H

D

H 3 C

H

E

CH3

H 3 C

STOP! END OF TEST.

Trang 9

ORGANIC CHEMISTRY SUBJECT TEST 1

ANSWER KEY

1 D

2 A

3 B

4 A

5 D

6 A

7 B

8 D

9 B

10 C

11 E

12 D

13 A

14 C

15 A

16 C

17 A

18 A

19 D

20 E

21 C

22 E

23 E

24 B

25.A

26 B

27 B

28 B

29 E

30 C

Trang 10

Explanations

A trivalent carbon with an unpaired electron does not possess an octet and can hence be considered electron deficient The free radical, then, just like carbocations, is stabilized by the presence of groups which can share electrons inductively (alkyl groups) or defuse the electron deficiency through resonance (conjugated systems) The order of free radical stability goes 3°>2°>1°>methyl Allylic and benzylic radicals are similar to tertiary radicals in terms of stability because of resonance delocalization The free radicals shown in choice A (benzylic), choice B (tertiary), and choice E (allylic) are all relatively stable, and therefore these three choices are incorrect The radicals offered in choices C and D are both relatively unstable, but the methyl radical depicted in choice D is more unstable than the primary radical in choice C Thus choice D, as the most unstable free radical, is the credited choice

Carbanions are stabilized either by electronegative substituent groups (absent in this case) or by resonance with _ electrons Choices D and E do not allow for any resonance stabilization and will therefore be less stable than the other three choices The anion in choice A allows the negative charge to be delocalized, through resonance, over nine other carbon atoms, three in each phenyl ring Choices B and C allow for delocalization over six additional carbons and three additional carbons, respectively Choice A thus allows for the greatest amount of charge delocalization of any of the choices offered, and is thus the most stable carbanion

The more energetically favorable a resonance structure is, the more it will contribute to the actual structure of the hybrid In other words, the actual electron density distribution of the hybrid molecule will more likely resemble the more stable resonance structures In looking for the resonance structure expected to make the least contribution, then, we are looking for energetically unfavorable structures It is highly unfavorable for electronegative species such as oxygen to bear a formal positive charge, thus making B the correct choice Choice A is the formal structural formula for acrolein It is the most stable of all the different resonance structures one can draw because there is no separation of charge Choices C and D are reasonable resonance forms which show how the conjugated double bonds delocalize the _ electrons and stabilize the molecule: the electronegative oxygen bears a formal negative charge which is certainly acceptable

Questions on the physical properties of organic compounds are best answered based on general chemistry principles, most notably those related to bond polarity and molecular interactions Hydrogen bonding is the strongest intermolecular force in which water can participate; alcohols also participate in hydrogen bonding, but this capability decreases with the increasing size of the alkyl portion of the alcohol molecule, because the relatively nonpolar alkyl group disrupts the hydrogen bonding network Ethanol, choice A, has a smaller alkyl group than propanol, choice B Ethanol thus has a greater capacity for hydrogen bonding and will be more soluble in water than the propanol will be Choices C and E show a ketone and an ether respectively; these compounds are not as soluble in water since, even though they have polar carbon-oxygen bonds, they have no hydrogens bonded to electronegative atoms that can contribute to hydrogen bonding Choice D, an alkene, is the least soluble in water of the choices offered

While this question is directly asking about the relative heats of hydrogenation of various polyenes, indirectly it is really asking, "Which of the following has the most stable _ system?" Recall that conjugation lends special stability to compounds with more than one _ bond Thus the question could be further translated to "Which of the following has the most extensive conjugated _ system?" Choice D is correct since 1,3,5-hexatriene has three double bonds in complete conjugation; it is thus more stable than choice E, for instance, because the first two double bonds in the compound 1,2,4-hexatriene are cumulated,

Trang 11

not conjugated Choice A, 1,3-pentadiene, is conjugated but has only two _ bonds, choice B, 1,4-pentadiene, has two _ bonds which are isolated, not conjugated, and choice C, 1,2-pentadiene, has two cumulated rather than conjugated _ bonds Each of these compounds is thus less stable “per double bond” than the 1,3,5-hexatriene of choice D

The reactant is a secondary alkyl halide; as such, it will react with iodide ions in an aprotic solvent via an SN2 pathway This fact is supported by the statement that the reaction proceeds with second order kinetics, the rate observation expected for

an SN2 reaction Since SN2 reactions are accompanied by inversion of configuration, in most cases, it follows that if the reactant is R, then the product will be S, vice versa We must therefore next determine whether the reactant is R or S It would be most helpful to convert the Newman projection shown into a Fischer projection from which to determine the R/S designation The carbon in the background of the Newman projection shown has three hydrogens attached to it, so it is a methyl group Writing a Fischer projection for this compound then requires that we place the methyl group, the ethyl group, the bromine atom, and the hydrogen atom (the four groups attached to the chiral carbon in the foreground of the Newman projection) in the appropriate spatial order

C

H CH2 CH3 Br

CH3

It should now be evident that the reactant is the R enantiomer of 2-bromobutane, and therefore the inverted product will

be the S enantiomer of 2-iodobutane, and choice A is confirmed as the correct answer

Amides are defined as organic compounds in which an amine functionality is directly bonded to a carbonyl carbon Choices A, C, and D are all simple amines (primary, secondary, and tertiary respectively); Choice E is a nitro compound,

carbon

N

S

O O

O -

H

N

S

O O

O H

H

A zwitterion is a molecule that has both positive and negative charges Usually amphoteric species, molecules that have both acid and basic functional groups, can form zwitterions (e.g amino acids) Sulfanilic acid has both an acid functional group (–SO3H) and a basic functional group (–NH2), and can therefore have both a positive and negative charge

simultaneously (see diagram above of conjugate base and acid) Zwitterions have strong intermolecular attractions due to ionic and hydrogen bonding, making D the correct choice Any correct answer choice has to involve intermolecular

attractions, since that is what provides for high boiling points relative to molecular weight No other answer choice addresses intermolecular attractions, so can be eliminated Additionally, all the other answer choices are stated incorrectly The

Định dạng
Số trang	15
Dung lượng	343,05 KB