NAME:

1

CEM 850 Final ExamDecember 11, 2003

This exam consists of 20 pages. Be sure to write your name on all pages of the exam. Pleasewrite legibly and draw all structures clearly. Good luck.

1. (10 pts) Estimate the pKa values of the following compounds and write the value in the boxbelow the corresponding compounds:

H O H

O H O

O HNH H NH H

H

H3C

O

CH2

H MeO

O

CH2

HO O

H NH H

NH

2. (3 pts) In the appropriate space show (a) the enol tautomer of A, (b) the keto tautomer of A,and (c) the Z-enolate derived from A.

b) c)

a)

AO O

CO

CF3

NAME:

2

3a. (2 pts) Circle the one cyclic,conjugated molecule possessing4n + 2p electrons among 1–3 thatyou predict would display thestability of an aromatic molecule?

3b. (5 pts) BRIEFLY explain why theother two molecules are not aromatic.

4. (4 pts) Vitamin E is a powerful antioxidant capable of capturing freeradicals that cause cellular damage in living organisms. The syntheticantioxidant BHT, commonly found in packaged foods, performs a similarfunction, preventing development of rancidity. Assuming that the freeradical species R• would initially abstract a hydrogen atom from the OHfunctionalities of these compounds, use the BHT framework to draw thefour resonance forms that would rationalize the stability of the resultingphenoxyl radicals.

OH

BHT

1 2 3

NAME:

3

5. Ions H2+ and He2

+ have similar bond strengths (ca. 60 kcal/mol) but neutralization of theirpositive charges by adding an electron results in bond strengthening for one and dissociationfor the other. Label the simple MO interaction pictures below (4 pts), and use them to helpexplain (4 pts) the similarity of the cations and the difference between the neutralized systems.

Explanation:

6. (4 pts) Consider the 4 unsaturated molecules below and answer the following questions.

O N

A B C

Br

D

(a) Which molecules can be polymerized via a cationic mechanism?

(b) Which molecules can be polymerized via a radical mechanism?

NAME:

4

7a. (7 pts) 1,2,3,4,5,6-hexachlorocyclohexane exists as a number of cis-trans isomers. Using theflat cyclohexane stencil and dashed-wedged lines, draw all of them.

7b. (3 pts) One of the isomers from 7a whose structure is shown below is aninsecticide (lindane, gammexane, kwell). Draw the two chair conformations ofthis isomer and indicate which is more stable.

Cl

ClCl

Cl Cl

Cl

NAME:

5

8. Joe Clueless, a typical first-yeargraduate student at Minnesota StateUniversity, predicted that an aldehydewas formed as a significant productduring reaction of propionyl chloridewith benzene:

(a) (5 pts) Provide a detailed mechanism for the formation of the presumed aldehydic product.

(b) (5 pts) Do you agree with Joe Clueless that the indicated aldehyde is a significant productformed during the Friedel-Crafts acylation? Provide a BRIEF explanation for your answer.

Cl

O O

HAlCl3

Cl

O O

HAlCl3

NAME:

6

9a. (6 pts) Draw the three pi(p) molecular orbitals of an allyl cation, indicating the symmetry of eachand the number of electrons in each.

9b (4 pts) Cyclopropyl cations open thermally to allyl cations. Below is an example. Add themethyl groups to the partial product drawing below, being sure to indicate their correctstereochemical positioning.

DH3C

H3C

H

H

10. (4 pts) If cyclobutane were flat, it would have exactly 90° C-C-C bond angles and couldconceivably use pure p-orbitals in its C–C bonds. What would be a possible hybridizationfor the carbon atoms of the molecule that would allow all of the C–H bonds to be equivalent?Exactly where would the hydrogens on each carbon be located?

NAME:

7

11a. (3 pts) The reaction below is not concerted but occurs by two consecutive concertedreactions. Complete the drawing of the intermediate species indicated below:

DPh

CH3

OH

NC CN

D CN

CNH3C

HO Ph

H

11b. (6 pts) Provide a detailed arrow pushing mechanism for the formation of the intermediatespecies you indicated above.

11b. (5 pts) Explain in writing the stereochemistry of both the intermediate and final products.

NAME:

8

12a. (3 pts) In the following aromatic substitution of indole, gramine (a flavoring constituent of beer)is produced as the major product. Substitution will occur preferentially at only one position ofthe indole. Provide the product.

major product

NH

H

O

H

HN , HOAc

12b. (3 pts) Consider the related substitution reaction with pyrrole. What is the product formed inthis reaction

major product

H

O

H

HN , HOAc

NH

12c. (5 pts) Explain the observed regioselectivities for the reactions of indole and pyrrole (6a-b).

NAME:

9

13. (8 pts) Provide the structures of A–D:

A

Mg(0); theCO2; then

H3O+/H2O

LiAlH4; then

H3O+/H2O

B, DCC,

CH2Cl2

H3O+/H2O

THF, heat

B

+

C

B (C7H12O2)

C D (C14H24O2)

14. (2 pts per box) Fill in the boxes, and provide stereochemistry if relevant.

OC C

OHt-BuOH

NAME:

10

majorproduct

mCPBA

mCPBAmajor

stereoisomer

Me

H

Note: you may ignore the stereochemistry of the product

N O

O2N Ph1.

MeCN

2. H2O, H3O+

N

NH

H

OO OO+

O

CO2H

CO2H1. heat

2. CH2N2

NAME:

11

ClHCl major

product

O

ethylvinylketone

NaOH, H2O

1. MeI2. Ag2O, H2O

3. heatH3C Ph

NMe2

CH3

1. MeI2. Ag2O, H2O

3. heatPh Ph

NMe2

CH3

1. mCPBA

2. heatPh Ph

NMe2

CH3

NAME:

12

1. NaOMe

2. H+, H2O, heat+ CH2(COMe)2

Br Br

+NaOEt

EtOH

CO2Et CHO

NaOMe

MeOH

H3O+

heat

O

+diethyl malonate

CHOPh3PCHCH3 OsO4

NaHSO3

OO

H

H+

NAME:

13

CHOPh3PCHCO2Et OsO4

NaHSO3

Pb(OAc)4

1. NH2OH, H+

2. pyrrophosphoric acid heat

O

NaOEt

EtOH

O

CO2Et

NO2

CH3

1. NaOMe,MeO OMe

O

O

2. H2, Pd/C

Reissert synthesis:

NAME:

14

heat

acid

Fischer indole synthesis:

HN

CH3

CH3

Strecker synthesis: 1.

2. HCl/ H2Ovaline • HCl

H2O, MeOH, NH4Cl, 45 °C

Darzens condensation:

CO2EtO

t-BuOK

15. (6 pts) Draw the isomeric C5H7Cl products for the following two reactions.

hu

CH3

ClD

NAME:

15

16. (5 pts) Propose a synthesis of the following amine from the given ketone and whatever elseyou need.

Osteps

NH

NAME:

16

17. (5 pts) Design a synthesis to prepare aniline from toluene; you may use any commonreagents.

NAME:

17

18. (5 pts) Design a synthesis of 2-benzylcyclopentanone from HOOC-(CH2)4-COOH and anyreagents of not more than 7 carbons.

NAME:

18

19. (6 pts) Provide a detailed arrow pushing mechanism for the following reaction, being sure toaccount for formation of a methoxy compound in which the stereochemistry of the oxygen haschanged.

OHH

O1. NaH

2. Me–IH

OMe

O

NAME:

19

20. (6 pts) Provide a detailed arrow pushing mechanism for the following reaction.

H+

CHO

CHO+ dimethylamine + acetone

NMe Me

O

NAME:

20

21. (6 pts) Provide a detailed arrow pushing mechanism for the following reaction that explains thefollowing rearrangement:

D

OHO

Bonus Question: (2 pts) Which former MSU chemistry graduate student served as the Munnice arena soloist, regularly singing the “Stars Spangled Banner” prior to MSU hockey games?a. Devi Adhikarib. Thomas Bannonc. Mrunal R. Thatted. Stephanos Tsirakogloue. Gang Zuo