Chemistry 310M/318MDr. Brent Iverson3rd MidtermNov. 30, 2005

NAME (Print): _____________________________

SIGNATURE: _____________________________

Please Note: This test may be a bit long, but there is a reason. I would like to give you a lot of little questions, so you can find ones you can answer and show me what you know, rather than just a few questions that may be testing the one thing you forgot. I recommend you look the exam over and answer the questions you are sure of first, then go back and try to figure out the rest. Also make sure to look at the point totals on the questions as a guide to help budget your time.

Note: You must have your answers written in blue or black pen if you want a regrade!!!!

Do not take this in red ink, as that is what we will use to grade it!

Please print the first three letters of your last name in the three boxes

Please answer the following before you begin:

Have you been to a recitation section since the last

midterm? ____________

10

9

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4

3

2

(23)

(12)

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(35)

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11

1

Page Points

Total

TScore

HW

12

14

Pg 1 _____________(23)Signature_________________________

1. (5 pts) Define Hammond's postulate in a concise fashion.

Hammond's postulate says that the transition state for an exothermic step resembles the reactants more than the products of that step, and the structure of the transition state for an endothermic step resembles the products more than the reactants of that step.

2. (1-4 pts each) Consider the following statements that refers to SN1, SN2, E1, E2 or a radical chain reaction mechanism. To which mechanism(s), if any, does each statement apply?

A. Involves a carbocation intermediateMechanisms

E1, SN1

B. Rearrangements can occur during these reactions E1, SN1 (radical chain reaction)

C. When reaction occurs at a chiral center on a pure sample of a single enantiomer, a single enantiomer product with inversion of configuration is created.

SN2

E. Involves an antiperiplanar transition state geometry

E2

F. The order of reactivity is 3° alkyl halides > 2° alkyl halidesG. The order of reactivity is methyl halides > 1° alkyl halides > 2° alkylhalides and not 3° alkyl halides

SN1, E2, E1

SN2

radical chain reactionH. For alkane starting materials, the order of reactivity is 3° hydrogens > 2° hydrogens > 1° hydrogens

E2I. The reaction that will occur when KOtBu is used

J. The reaction that will occur when Br2 and light are used

radical chain reaction

K. The reaction that will occur when HBr and peroxides with light are used radical chain reaction

L. The reaction that will occur when NBS and light are used radical chain reaction

M. Is promoted by polar protic solvents E1, SN1

D. When reaction occurs at a chiral center on a pure sample of a single enantiomer, a mixture of product enantiomers will be created

SN1, radical chain reaction

Signature_________________________ Pg 2 _____________(12)

3. (3 pts) For the following series of compounds, circle the one with the highest boiling point.

H3CCH2

CH2CH3

H3CCH2

CH2OH

HOCH2

CH2OH

4. (3 pts) For the following series of compounds, circle the one with the greatest solubility in water.

5. (3 pts) For the following series of cations, circle the most stable cation.

3° 2°

1°

allylic2°

1°

H3CCH2

CH2CH3

H3CCH2

CH2OH

HOCH2

CH2OH

6. (3 pts) For the following series of radicals, circle the most stable radical.

Signature_________________________ Pg 3 _____________(18)

7. (13 pts total) For each set of reagents below, draw the key transition state that occurs during the indicated reaction. We do not want the entire mechanism or products, just the first key transition state. Use dotted lines to indicate bonds that are in the process of being broken or made. Write any formal charges that you think are important. On the starting structures, draw all appropriate arrows to indicate the flow of electrons.

A.

Transition State

Transition State

H3CC

CH3

H BrSH +

C

H

CH3H3C

BrSSN2

B.

HC C

IH3CH3C

CH3

HE2OH3C +

OH3CH

C C

IH3C

H3C

CH3

H

H

anti-periplanar geometry

8. (5 pts total) For the set of reagents below, draw the first key intermediate that occurs during the indicated reaction. We do not want the entire mechanism or products, just the first key intermediate. Write any formal charges that you think are important. On the starting structures, draw all appropriate arrows to indicate the flow of electrons.

C.

Intermediate

H3CC

CH3

H3C BrOH +

SN1, E1

HC

CH3

H3C CH3

Br

CCH3CH2C

CH3H

HBr

H3C

CH3

Br

H

CH2CH3H3C

H CH3

Br

CH3

H

Br

HH

H

CCH

BrH3C

CH3

HH3CH2C

CH3

CCH3CH2C

H3C

CH3

H

Signature_________________________ Pg 4 _____________(20)

9. (12 pts total) Before the following two alkyl halides react with the strong base via an E2 mechanism, they must adopt a reactive conformation. In the space provided, draw the alkyl halide shown in this reactive conformation that must be present for an E2 reaction to take place. On the reactive conformation you draw, circle the atoms of the alkyl halide that will be removed in the reaction After you draw the E2 reactive conformation, draw the predominant product of the E2 reaction of the alkyl halide with strong base (KOtBu). You may use any type of drawing you wish for these, namely line angle drawings, Newman projections, or chair conformations as appropriate. Please read these directions again so you know what we want!!!

E2 reactive conformationanti-periplanar

KOtBu

E2

E2 Product

E2 reactive conformationaxial

KOtBu

E2

E2 ProductZaitsev product

10. (8 pts) In the following two sentences, fill the in the blanks with the appropriate numbers.

A) In an SN__ reaction, the "__" in the name means that in the key slow step of the reaction both the

alkyl halide and the nucleophile are involved, so their concentrations are both proportional to the rate

of the reaction.

B) In an SN__ reaction, the "__" in the name means that in the key slow step of the reaction only the

alkyl halide is involved, so its concentration alone is proportional to the rate of the reaction.

Z alkene product

2

1

2

1

On your answer to question 9 above, did you remember to circle the atoms on the reactive conformations that will be removed?

Signature_________________________ Pg 5 _____________(35)

10. (23 pts total) Complete the following intiation and propagation steps for the addition of HBr via a free radical chain reaction mechanism. Use appropriate arrows to show movement of electron density, and show all non-bonding electrons as dots and show any formal charges.

Initiation

OR O R R O R O+

R O + BrH + R OHBrsame species

Propagation

BrC

CC

H

H

H

H

H

H

+C

CC

H

H

Br

H

H

HH

CC

C

H

H

Br

H

H

HHBrH

Br

+

same specie

s

same species

CC

C

H

Br

H

H

HH

H H

same species

Products

+

hν

11. (12 pts total) Complete the following mechanism. Use appropriate arrows to show movement of electron density, and show all non-bonding electrons as dots and show any formal charges. Show all products of each step and use wedges and dashes to keep track of stereochemistry.

OH P

Br

Br BrO

H

PBr

BrBr

Br

Br

H CH3 H CH3

P

Br

HO Br

CH3H

Products

R

S

CCH3C

C

Br

H3CH

CH2CH3

C

Br

H3CH3C

CH3

C

Br

H3CH3C

CH2CH3

Br

Na

Na N3

CH3CH2OH

SN2

SN2

E2

SN1/E1

E2

CH3CH2O Na

CH3

I

CH3CH2O Na

C

OCH2CH3

H3CH3C

CH3

CH3CH

CH2CH3

N3

C CCH3

H3C

H3C

H

CH3

CH3

C CH2H3C

H3C

Signature_________________________ Pg 6 _____________(27)

12. (5 or 7 pts each) The following reactions all involve chemistry of alkyl halides. Fill in the box above the arrow with the mechanism that will be followed (SN2, E2, etc.). Then draw only the predominant product or products and please remember that you must draw the correct stereoisomers. When a scrambled mixture is formed, you must write "scrambled" under both structures EVEN THOUGH YOU DREW BOTH STRUCTURES. For SN1/E1 reactions you must draw both types of products.

+

C.

A.

E.

B.

+

D.

Inversion

Zaitsev product

+

+

Only product possible due to axial requirement

+

Signature_________________________ Pg 7 _____________(22)

Br2

Br2

NBS

HBr

HBrROOR

HBr

Br

H

Br

Br

Br

Br

Br

Br

H

Br

Br

13. (3 or 5 pts each) For the following, complete the reactions with the predominant product or products. You must indicate stereochemistry with wedges and dashes. If a racemic mixture is created, you must write "racemic" under the structures.

not chiralhν

hν

racemic(anti addition)

(reacts at moresubstituted C atom)

+

racemic

hν(non-Markovnikov)

(Markovnikov)

(allylic halogenation)most stable alkene

+

OH1° alcohol

Br

Protonation of the alcohol function followed by an SN2 reaction with bromide.

OH

OH

OH

OH

H2

H H

OH

O

H

O

2 H2 O

Signature_________________________ Pg 8 _____________(22)

13. (3 or 5 pts each) For the following, complete the reactions with the predominant carbon containing product or products. You must indicate stereochemistry with wedges and dashes. If a racemic mixture is created, you must write "racemic" under the structures.

1) OsO4

2) NaHSO3 / H2O

Pd°

1) O3

2) (CH3)2S

racemic

1) (sia)2BH2) H2O2 / HO

Pd°

HgSO4H2SO4H2O

H2

OH

PBr3

HBr

Large excess

Signature_________________________ Pg 9 _____________(25)

13. (3 or 5 pts each) For the following, complete the reactions with the predominant carbon containing product or products. You must indicate stereochemistry with wedges and dashes. If a racemic mixture is created, you must write "racemic" under the structures, and if the stereochemistry of a chiral center is scrambled, you must write "scrambled".

Na° / NH3

Lindlarcatalyst

Na°

HO

of HBr

Think about this next one!

OH

O

Br

Na

Br Br

H3CBrBr

Br

scrambled(SN1)

Signature_________________________ Pg 10 _____________(19)

Br2

Br

Cl

ClCl

Cl

Cl2

14. These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned. Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction.

?

A) (7 pts)

hν Recognize this as the product of Cl2 reacting with an alkene.

12

345

6

racemic

12

345

6

12

345

6

KOtBu

E2

Recognize this alkene as being the Zaitsev product from the alkyl halide that in turn comes from the alkane starting material

H

H H

NaNH2

Br

HBr

H2C CH2

HO H

H OH

OR

B) (12 pts)

+racemic

H2O / H2SO4

1) H2O / Hg(OAc)22) NaBH4

H2Lindlar Catalyst

?1 2 1 2 12 3

4

12 3

4

Recognize that each of the two carbon starting materials had to be combined to give the four carbon product. Also, the only way you know how to an alcohol product is from hydration of an alkene, so this must be the last step. Putting both pieces of information together, you need to make the alkyl halide from the alkene to react with the alkyne anion, followed by reduction to the alkene.

PBr3

Br2

Br

H

O O

14. These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned. Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction.

Signature_________________________ Pg 11 _____________(14)

C) (7 pts)

?

KOtBu

E2

D) (7 pts)

?

KOtBu

E2

hν1) O3

2) (CH3)2S

123

4

56

12

34

5

6

1 2 3 4 56

Recognize that the alcohol product is derived from non-Markovinikov addition to a terminal alkene. The terminal alkene came from an E2 reaction on the akyl halide made from the secondary alcohol starting material using PBr3. Note that in the E2 step only the terminal alkene can be formed because there is no H atom on the other carbon.

Recognize the product has the same number of carbon atoms as the starting material and the two C=O groups indicate an ozonolysis reaction was the last step. The ozonlysis must take place on an alkene, that can be made from an E2 reaction on an alkyl halide that is the predominant product from halogenation of the starting methylcyclopentane.

OHOH

123

4

56

Br1) BH3

2) H2O2 / HO

14. These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned. Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction. This is a tricky one, so be creative. Please try to give us No BS!

Signature_________________________ Pg 12 _____________(13)

E) (13 pts)

?Br

Br

Br Br

Br

H OH

H OH

HO H

HO H

racemic

KOtBuE2

NBShν

H2Pd°

KOtBuE2

1) OsO4

2) NaHSO3 / H2O

Recognize this last step as coming from the OsO4/NaHSO3H2O reaction. Note the syn addition of this reaction requires a trans alkene starting material

Recognize that the tricky part of this synthesis is moving the double bond over. The only way to accomplish this is through the allylic halogenation reaction (NBS/hν) followed by hydrogenation then an E2 to give the desired trans Zaitsev product. Note the subtle hint about the required NBS reaction in the directions ("No BS")

H3CC

OH

OH3C NH3 H3CH2C SH

NHN

NH

O

O

O

OH2C

OO

N

S

H

H

H

H

NHN

NH

O

O

O

OH2C

OO

N

S HH

H

H

H

HH

Signature_________________________ Pg 14__________(12)

18. (12 pts) I promised you this one! Complete the following three structures by adding appropriate numbers of valence lone pair electrons, H atoms, and formal charges to the atoms in the boxes. You must adjust your answers to indicate the predominant species at each indicated pH value. (You do not have to add anything such as H atoms to atoms not drawn in the boxes.) This problem is testing your understanding of the relationship of protonation state to pH to pKa values for certain functional groups we have discussed. Next, in the space provided, write the overall charge on each structure at the indicated pH. For your reference, here are the relavant pKa vaules:

pKa = 4.76pKa = 10.64 pKa = 8.5

pH = 13

pH = 6.5

Total charge on molecule:______

Total charge on molecule:______

-3

0