midterm iii a key 2321 f13

Chem 2321-003 Midterm III F‘13

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Chemistry 2321-003

Organic Chemistry I

Midterm Examination III 11:00 am – 12:20 pm

Form A

November 26, 2013

J. Jeon

Name: ________________Key________________ Total /100 please print (last, first)

ID #: ______________________________________

• There are 110 points on this exam and the eight exam pages. • For the multiple choice questions 1-9, select the best answer and darken completely with a

pencil the space corresponding to that answer in scantron (form # 882-E). • Look over entire exam before starting and carefully read all instructions. • You are free to use molecular models during the exam. • For questions 10 and 13, I will not reconsider grades for answers written in pencil.

Have fun!


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1. (5 pts) These problems are about the IUPAC (International Union of Pure and Applied Chemistry) nomenclature of organic compounds. Select the best name for the following molecule. d)

Me

Me

Me

a) (S)-3-methylhept-4-yne b) (R)-3-methylhept-4-yne c) (S)-5-methylhept-3-yne d) (R)-5-methylhept-3-yne e) (S)-4-methylhept-5-yne

2. (5 pts) Consider the following addition reaction. Which of the following structures is the correct structure of the intermediate B? e) > hydration of alkyne: enol-keto tautomerization

H2SO4HgSO4 (cat.)

H2O

H

A B C

O

Me

a) b) c) d) e)HgSO4 OH

OHOH

3. (5 pts) Predict the major product of the following reaction? b) > ozonolysis of alkenes

1) O3

2) Me2S

HH

Me

Me

a) b) c) d) e)

Me

MeO

Me

MeHOOH

OH

Me

O H

Me

O

Me

MeSMe

Me


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4. (5 pts) Predict the major product of the following stereospecific reaction? d) > halohydrin

Br2

H2O

a) b) c) d) e)

Br Br Br Br Br HO Br

Br

5. (5 pts) Which of the following bases cannot be used to deprotonate the terminal alkyne A leading to the product B via a carbon-carbon bond formation? a) > basicity [by utilizing either pka values or comparing stabilities of conjugated bases (A.R.I.O.)]

1) base

2)

H

A MeBr

B

Me

e)a) b) c) d)ONa

Me

LiLi allNaN

H

H

(n-BuLi)(PhLi)

6. (5 pts) List the following reactions in order of decreasing rate of reaction? c) > stability of the resulting carbocation intermediates

HBr

ether (solvent) Br

HBr

ether (solvent)MeMeBr

HBr

ether (solvent)MeMeBr

Me Me

I.

II.

III.

a)

b)

c)

d)

e)

I

II

III

II

I

>

>

>

>

=

II

III

II

I

II

>

>

>

>

>

III

I

I

III

III

fastest slowest


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7. (5 pts) Consider the following reactions (I and II). These two radical reactions produce a mixture of regioisomers (B/C from the reaction I and D/E from the reaction II). The energy diagram of the hydrogen abstraction step in these transformations are shown below, which constitute two individual propagation steps (1. hydrogen abstraction and 2. halogen abstraction):

I.

A

+ Cl2

B

+Cl

C

Cl

ROOR

heatingII.

A

+ Br2

D

+Br

E

Br

+ HCl

+ HBr

ROOR

heating

E

Reaction Coordinate

The hydrogen abstraction step in the chlorination reaction

E

Reaction Coordinate

The hydrogen abstraction stepin the bromination reaction

A

Eac1 Eac2

Eac3

Eac4

A

B1

C1

D1

E1

7. (5 pts) Which of the following statements is true? a)

a) The reaction II is more regioselective.

b) Based on the Hammond postulate the transition state structures of the hydrogen abstraction step in the reaction I more closely resemble intermediates generated during this step.

c) The rate of the reaction II is faster.

d) The activation energy difference (ΔEac) leading to the primary and secondary radical intermediates in the reaction I is larger than one in the reaction II.

e) The entropy of system of the reaction I is negative.


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8. (5 pts) Of the following molecules, which most readily undergoes a unimolecular elimination reaction (E1)? c) > the rate of the E1 mechanism is rate = k[substrate], so that again the stability of the resulting carbocation intermediates becomes important.

a) b) c) d) e)Br

BrBr Br

Br

9. (5 pts) Of the following covalent bonds, which has the greatest bond dissociation energy? b) > this question asks about which bond is the strongest one.

Hb

Ha

Hc

Hd

Me

a) Ha b) Hb c) Hc d) Hd e) none

10. (10 pts) Draw the major organic product(s) (NO associated mechanism) of the each reaction in the boxes provided. Be sure to indicate stereochemistry if applicable.

Me H2

Lindlar's catalyst(Pd/BaSO4, quinoline)

CH3OH

1) OsO4

2) NaHSO3 H2O

Me

N

quinoline

A

B C

Me

Me

Me

Me OH

OH

Me

Me OH

OH

or


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11. (15 pts) Consider the following addition reaction.

a) (10 pts) Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) for the following reaction [only step 1) A to B]. Specify the correct regio- and stereochemistry where appropriate. Draw the major product (B) in the box.

b) (5 pts) Draw the major product (C) of the following reaction [B to C] in the box (only product, no mechanism).

●Bonus (5 pts): Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) for the following reaction [only step 2) B to C].

1)

Et 2) H2O2, NaOH

A B C

BH

Et

B

HEt

OH

H

Anti-Markovnikov addition then oxidation (see pages 415 and 475)

Et

B

H

Et

B

H

B

O O HH NaOH

O OH Et

B

H

O OH

see page 415


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12. (15 pts) Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) for the following reaction. Draw the major product (B) in the box.

NBS (N-Bromosuccinimide)

N

O

O

BrNBS, hv

BA

Hint: During this reaction, small quntities of molecular bromine (Br2) is generated via the reaction below. Utilize

this bromine in the above reaction.

N

O

O

Br + N

OH

O

+ BrH Br Br N

OH

O

+ Br Br NH

O

O

+ Br2

succinimide

BrHH

+ HBr

Br Br

NBS + HBrfrom hint

Br

+ BrH

free radical chain reaction

N

O

O

Brhv

N

O

O

Br+


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13. (15 pts) Consider the following addition reaction.

a) (10 pts) Provide the detailed arrow-pushing mechanisms (step by step, draw all the intermediates) of the first step [1) Hg(OAc)2, H2O] for the following reaction [A to B] [do not provide the mechanism of the second step, i.e. 2) NaBH4]. Specify the correct stereochemistry where appropriate. Draw the major product (B).

b) (5 pts) Draw the major product (C) of the following reaction [A to C] in the box (only product, no mechanism).

1) Hg(OAc)2, H2O

2) NaBH4

A C

Me

Me

B

H2SO4, H2OMe

Me

MeMe

OH

MeOH

MeMe

Me

Me

Oxymercuration-demercuration technology (A to B) was invented to prevent the inevitable carbocation

rearrangement in an acid-catalyzed hydration reaction (A to C).

MeHg

OAc

MeMeHg

H2OHg

MeH HgOAc

H2O

Hg OAcAcO

OAc

Me Me Me MeMe Me Me Me

OAc

H

OH H OH

2) NaBH4

MeH H

MeMe

OH

no mechanismdiscussion

B

and enantiomers

OH

OH

carbocationrearrangement

minor products(racemic mixture)

nucleophilc attackMajor product

2°

3°

+OH OH

OH

H SO4H

C

A

(a similar question was discussed in our midterm II.)

***** End of Exam ***** You may pick up your exam on Thursday, December 3 (in class). Thank you!

midterm iii a key 2321 f13

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