Organic chemistry section test (2)

Bromine: axial, t-butyl: equatorial D?. Bromine: equatorial, t-butyl: axial EA. Bromine: either axial or equatorial, t-butyl: equatorial 23.. A single alkene product is formed, and is

MCAT Subject Tests

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OR G A N I C CH E M I S T R Y SU B J E C T TE S T 2

Organic Chemistry Subject Test 2

1 Which of the following is the most stable carbocation?

A

H 2 C CH+

B

C

CH3 CH2 CHCH2 +

CH3

D

+

E

CH2 CH2

2 Which is correctly paired?

A

R CH

NH2

C

O

B

R C NH

O

C

D

R CHOH

C OH

O

E All of the above

Questions 3-6 refer to the following choices:

A enantiomers

B diastereomers

C structural/constitutional isomers

D conformational isomers

E tautomers

3

H OH

CH3 and CH3 CH2 CH2 OH

4

C

C OH

H

CH2 OH

CHO OH

H

and

C

C H OH

OH

H CHO

CH2 OH

5

6

C

CH3

C 2 H 5

H OH and C

C 2 H 5 OH

H

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1

7 What is the hybridization of the carbonyl carbon in

N,N-dimethylformamide?

A sp3

B sp2

C sp

D sp3d

E sp3d2

8 A compound is separated from an ethereal mixture by

extraction with cold, aqueous NaHCO3, then recovered

by addition of HCl to the extract Which of the

following is a likely identity of the compound?

A CH3(CH2)7CH2OH

B CH3(CH2)7CHO

C CH3(CH2)7CH2NH2

D CH3(CH2)7COOH

E CH3(CH2)7COONa

9 1,3-Cyclopentadiene reacts with sodium metal at low

temperatures according to:

Na

What is the best explanation for this observation ?

A The reactant is more unstable at reduced

temperatures

B The cation formed is stabilized by aromaticity

C Sodium metal is highly specific for cycloalkenes

D The rehybridization of the saturated carbon atom

provides additional stability to the product

E The anion formed is stabilized by aromaticity

10 Which of the following is an appropriate resonance

form of the conjugate base of p-aminobenzoic acid?

H 2 N

O

O

C

O

O

N

H

H

C

O

O

N

H

H

C

O

O

O

O

A

B

C

D

E

11 Which of the following statements is true of acetone?

A It exists as a pair of tautomers, of which the keto form predominates

B It exists as a pair of tautomers, of which the enol form predominates

C It is useful as a solvent due to its unusually high boiling point

D It is useful as a solvent due to its polar, protic nature

E It is useful as a solvent due to its lack of reactivity toward nucleophiles

12 The compound pictured below is a member of which compound class?

COOH

O C(CH3 ) 3

A carboxymethoxybenzenes

B methoxybenzoic acids

C propoxybenzoic acids

D t-butoxybenzoic acids

E carboxycumene oxides

OR G A N I C CH E M I S T R Y SU B J E C T TE S T 2

13 Which of the following could be the formula of an ester?

A C7H12O

B C7H12O2

C C7H14O

D C7H16O2

E C6H12O

14 What is the rate law for the elimination (E2) reaction

shown below?

← H2C=C(CH3)2 +t-BuOH + KBr

A rate = k[t-BuBr]

B rate = k[t-BuBr][t-BuO–]

C rate = k[t-BuBr]2

D rate = k[t-BuO–]2

E rate = k[t-BuOH][H2C=C(CH3)2]

15 Cyclohexane has how many fewer hydrogen atoms per

molecule than does n-hexane?

A 0

B 1

C 2

D 3

E 4

16 Which of the following has the most exothermic heat of

hydrogenation?

A Cycloheptene

B Cyclohexene

C Cyclopentene

D Cyclobutene

E Cyclopropene

17 What are the bonding types and degree measures of the

bond angles normally associated with the hybridizations

sp2 and sp3, respectively?

A σ 109.5°, and σ 109.5°

B σ 109.5°, and π 109.5°

C σ 120°, and π 120°

D π 120°, and σ 120°

E π 120°, and σ 109.5°

18 How many distinct organic compounds have the molecular formula C5H12?

A One

B Two

C Three

D Four

E Five

19 Which of the structures below is most stable?

CH3

H 3 C

Cl

CH3

CH3

CH3

CH3

CH3

CH3

Cl

A.

B.

C.

D.

E.

20 Which of the choices below best describes the relationship between Z and E isomers?

A Enantiomers

B Geometric isomers

C Conformational isomers

D Structural isomers

E Tautomers

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3

21 What is the approximate C-N-C bond angle in

diethylamine?

A 107°

B 110°

C 120°

D 150°

E 180°

22 What are the positions occupied by the bromine atom

and the tert-butyl group respectively in the most stable

conformation of

trans-1-bromo-3-tert-butyl-cyclohexane?

H

Br

C(CH3 ) 3

H

A Bromine: axial, t-butyl: axial

B Bromine: equatorial, t-butyl: equatorial

C Bromine: axial, t-butyl: equatorial

D Bromine: equatorial, t-butyl: axial

E Bromine: either axial or equatorial, t-butyl:

equatorial

23 What is the IUPAC name of the following compound?

CH3 CH2 CHCH2 CCH 2 CH2 CH2 CH3

CH3 CH2 C H 3

C H 3

A 5-ethyl-3,3-dimethylnonane

B 3-ethyl-5,5-dimethyloctane

C 3-ethyl-5,5-dimethylnonane

D 7-ethyl-5,5-dimethyloctane

E 7-ethyl-5, 5-dimethylnonane

24 What is the product of the reaction below?

CH3 Cl + CH 3 O - Na+

A CH3CH2OCH2CH3

B CH3OCH2CH3

C CH3OCH3

D CH2=CH2

E CH3CH3

25 How many different stereoisomers does the following compound have?

HOOC C

H

OH

C OH

H

C

OH

C OH

H

H

H

A 2

B 3

C 4

D 8

E 16

26 Which of the following compounds will exhibit the greatest dipole moment?

A (Z)-1,2-Dichloro-1,2-diphenylethene

B (E)-1,2-Dichloro-1,2-diphenylethene

C 1,2-Dichloro-1,2-diphenylethane

D 1,2-Dichloroethane

E 1,2-Difluoroethane

27 How many structural isomers of C3H6Br2 are capable of exhibiting optical activity?

A 0

B 1

C 2

D 3

E 4

28 Which of the compounds below would be the best starting material for the synthesis shown?

?

CH3 CH2 MgBr

CH3 (CH 2 ) 6 CH3

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

OR G A N I C CH E M I S T R Y SU B J E C T TE S T 2

29 What is the major product of the elimination reaction

below?

H 3 C C C C CH3

H

Cl H

H

H

CH3

KOH alcohol

A H 3 C C C C CH3

H

H

CH3

H

B. H 3 C C C C CH3

CH3

H

H 3 C C C C CH3

H

H

H

H 3 C C C C CH3

CH3

H

H

Cl

H 3 C C C C CH3

H H

C.

D.

E.

H 3 C

30 A mixture of alkyl halides is subjected to elimination

(E1) with one mole of aqueous acid and alcohol If the

reactant mixture initially contains one mole each of

n-propyl chloride and ison-propyl chloride, what can be

predicted about the product mixture?

+ /H2 O

CH3 CH2 OH

A A single alkene product is formed, and isopropyl

chloride is present in excess

B A single alkene product is formed, and n-propyl

chloride is present in excess

C Two distinct alkene products are formed, and

n-propyl chloride is present in excess

D Two distinct alkene products are formed, and

isopropyl chloride is present in excess

E No reaction occurs because both alkyl halides used

are inert to elimination (E2) STOP! END OF TEST.

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5

ORGANIC CHEMISTRY SUBJECT TEST 2

ANSWER KEY

1 B

2 E

3 C

4 B

5 D

6 A

7 B

8 D

9 E

10 C

11 A

12 D

13 B

14 B

15 C

16 E

17 E

18 C

19 A

20 B

21 A

22 C

23 C

24 C

25 D

26 A

27 B

28 D

29 A

30 B

OR G A N I C CH E M I S T R Y SU B J E C T TE S T 2

Explanations

1 B

Cation stability, like that of the free radicals, declines in the order 3°>2°>1°>methyl Choices C, D, and E, as primary cations, can therefore be disposed of first (Each would quickly rearrange via hydride shifts to form tertiary or benzylic

cations.) Of the remaining choices, choice A is a vinylic cation which is rather unstable due to the high s character of the

sp2 orbital The _ bond and the empty orbital are perpendicular to each other and hence the carbocation cannot be stabilized through charge delocalization Choice B, however, is an allylic cation which can be stabilized via resonance (or

equivalently, delocalization of the _ electron cloud):

C H 2 C H C H 2 C H 2 C H C H 2

2 E

All of the structures listed are correctly paired with their description Choice A is an ester (RCOOR) that has a amine substituent Choice B is an amide (RCONR2), choice C is a simple (in this case primary) amine, and choice D is an acid with a hydroxy (alcohol) substituent on the α-carbon

3 C 4 B 5 D 6 A

Both compounds in #3 have the same atoms, but the connectivity among them is different These are structural or constitutional isomers by definition

The two compounds listed in #4 have the same two chiral centers on each and differ in the configuration around only one of these; they are thus not mirror images of each other They are therefore diastereomers

The two compounds in #5 are chemically identical, differing only in their rotation about a single bond, in this case the central carbon-carbon bond These are referred to as conformational isomers

The last pair of compounds are non-superimposable mirror images and are recognizable as such because the two compounds have two of the groups interchanged about a chiral center By definition, they are enantiomers Note that another switch between any two of the four groups will bring the molecule back to its original configuration

7 B

A carbonyl carbon is one that is double bonded to an oxygen Since the carbon contains one π bond and three σ

bonds (one double bond and two single bonds), it must be sp2 hybridized Note that we do not need to know the structure of

N, N-dimethylformamide to answer this question

N

N,N -Dimethylformamide

8 D

The correct answer choice has to be a compound that is hydrophobic (since it started in the ether layer), but when reacted with a weak base becomes a water soluble salt Choice A is an alcohol which is not acidic enough to react with

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7

sodium bicarbonate, a weak base It would remain dissolved in the ether Choice B is an aldehyde, which can be

eliminated for the same reason as A Choices C and E are both bases, so neither will react with another base Choice D,

nonanoic acid, will react with sodium bicarbonate and form sodium nonanoate, a water soluble salt Extra Q: How can you tell you have a carboxylic acid by observing the addition of sodium bicarbonate? A: In addition to the formation of a

salt, carbonic acid is also formed (H2CO3) which can decompose into H2O and CO2 you'll see bubbles!

9 E

When 1,3-cyclopentadiene reacts with sodium, it goes from a nonaromatic to an aromatic compound A planar cyclic compound is aromatic if it satisfies Huckel's rule—that is, it has (4n+2) π electrons, where n is any integer The product of the reaction has 6 π electrons, so is therefore aromatic An aromatic compound is very stable because the π electrons are

delocalized throughout the ring In this reaction the products are much more stable, so the reaction will be spontaneous

10 C

When aminobenzoic acid loses a proton, the conjugate base assumes a charge of –1 Therefore, any resonance structure must also posses the same net charge Only answer choices B and C satisfy this requirement, and B can easily be eliminated because nitrogen is not part of the benzene ring

11 A

Acetone is a compound commonly used as a solvent to promote SN2 and E2 reactions because it is aprotic and polar Since it cannot form strong intermolecular bonds and is of low molecular weight it has a low boiling point Acetone exists

in two forms, with the keto form predominating by 99% This is because the carbon-oxygen double bond (the carbonyl bond) is much stronger than the carbon-carbon double bond

C H 3

C

O

C H 3 C H 3

C

O H

C H 2

12 D

Benzoic acid is a benzene ring with a carboxylic acid function attached directly This eliminates choices A and E

Meta to the acid is a t-butoxy group, leaving only choice D

13 B

An ester must have at least two oxygens; both of which are bonded to the carbonyl carbon (one via a double bond and one via a single bond) This leaves only choices B and D The maximum number of hydrogens a seven carbon ester can have is 14, This happens when all the other carbon atoms (except for the carbonyl carbon) are saturated One possibility is given below:

H 3 C

H 2

C

C

H 2

H 2

C

C

H 2

C

O

O C H 3

Again, this is the maximum number of hydrogen atoms So choice D, with 16 H’s, cannot be correct Choice B is the correct response The fact that it has two fewer H’s means that the compound is unsaturated One possibility for the structure of choice B is as follows

OR G A N I C CH E M I S T R Y SU B J E C T TE S T 2

H 3 C

H 2

C

C

H 2

H

C

C

H

C

O

O C H 3

14 B

For SN2 and E2 reactions, the rate law is first order with respect to both the nucleophile and the substrate In this

reaction the nucleophile is the t-butoxide anion (t-BuO-) and the substrate is t-butyl bromide (t-BuBr) Thus the rate law

must be B

15 C

Cyclic hydrocarbons have the general formula of CxH2x, while straight chain hydrocarbons have the formula CxH2x+2,

giving a difference of two Cyclohexane has 12 hydrogens, while n-hexane (straight chain) has 14

C

C

C

C

C

C

H H

H

H

H

H

H

H

H

H

H

H

C

C

C

C

C

C

H

H

H

H H

H H

H H

H H

H

H

H cyclohexane, C6 H 12 n -hexane, C6 H 14

16 E

Heat of hydrogenation (_HH) is the amount of energy released when π bonds are converted to σ bonds by the addition

of hydrogens The greater the _HH of a molecule, the greater the potential energy it has The more potential energy a molecule has, the less stable it is By comparing the _HH of different molecules, their relative stabilites can be obtained Cyclopropene, a three-membered ring, has the greatest bond strain, and is the most unstable It will therefore release the most energy upon hydrogenation, so will have the greatest _HH

17 E

sp2 hybridized carbons are involved in a double bond, which consists of one sigma and one pi bond The bond angle is about 120°:

C

120°

120°

sp2 hybridized

sp3 hybridized carbons are involved in single (sigma) bonds only, and the bond angles are about 109.5°

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9