exam answers quiz keys

CHEM 238B, Winter 2010 QUIZ KEYS

Name _________________

Section ________________

CHEM 238B Quiz 1

Version A

1. Give an IUPAC name for each of the following structures

a. b. c.

2. Draw an arrow-pushing mechanism for the following problem and show the major product that

will result from the reaction.

Br

Br

(1Z, 3E, 5Z)-1,6-

dibromohexa-1,3,5-triene

o-fluorophenol

4-methyl-1-phenyl

cylcohexan-1-ol


3. Classify the following heterocyclic molecules as aromatic, anti-aromatic, or not aromatic,

according to Huckel’s rule.

a. b.

antiaromatic aromatic

(not aromatic okay)

4. Give the major product for each reaction shown here:

5. Write the major product of this reaction.

O

HN

HB

NH

BH

NH

HB

1 mol. HCl

-80oC

1 mol. HCl

50oC

1 mol. Br2

-80oC

1 mol. Br2

50oC

2 mol. Br2

25oC

Cl

Br

BrBr

Br

Cl

Br

Br

Br

Br

H

H

1,2-addition @ cold temperature is kinetic control

1,4-addition observed w/ heat is thermodynamic control

1 2 3 4

12

34

Br2

H2O

Br

OH

hydration of bromonium intermediate occurs at

benzylic position, not tertiary


Name _________________

Section ________________

CHEM 238B Quiz 1

Version B


a. b. c.




a. b.

Aromatic Aromatic

Br

Br OH

NO2

NH HN

HB

NH

BH

NH

HB

(1Z, 3Z)-1,4-dibromohexa-

1,3,5-triene

p-nitrophenol 4-ethyl-1-phenyl

cylcohexan-1-ol

Br2

H2O

Br

OH

hydration of bromonium intermediate occurs at

benzylic position, not tertiary





1 mol. HCl

-80oC

1 mol. HCl

50oC

1 mol. Br2

-80oC

1 mol. Br2

50oC

2 mol. Br2

25oC

Cl

Br

BrBr

Br

Cl

Br

Br

Br

Br

H

H



1 2 3 4

12

34


Name _________________

Section ________________

CHEM 238B Quiz 1

Version C


a. b. c.


Br Br

(1Z, 3Z)-1,3-dibromohexa-

1,3,5-triene

m-nitrotoluene

4-t-butyl-1-phenyl-

cylcohexan-1-ol

1 mol. HCl

-80oC

1 mol. HCl

50oC

1 mol. Br2

-80oC

1 mol. Br2

50oC

2 mol. Br2

25oC

Cl

Br

BrBr

Br

Cl

Br

Br

Br

Br

H

H



1 2 3 4

12

34







a. b.

antiaromatic aromatic

(credit for not aromatic, can be if O’s are sp3)

O

O

HN

HB

NH

BH

NH

HB


Name _____________________

Section ____________________

CHEM 238 B Quiz 2

Version A

1) Draw the missing intermediate and product in the reaction below; where E+ is an electrophile.

2) Circle the choice which best describes the relative rates of intermediate and product formation in

the reaction above.

a) Same

b) Slow, Fast

c) Fast, Slow

3) For the pair of compounds given below choose which one will react faster with the indicated

reagent and write a chemical equation for the faster reaction.

Fluorobenzene or (trifluoromethyl)benzene with benzyl chloride and aluminum chloride


4) Write a structural formula for the compound:

(Z)-2-Phenyl-2-butene

5) Provide the reagents required at each step of the provided reaction.

1) AlCl3

2) NBS

3) strong base, NaOEt KOtBu etc

4) Zn0 (Hg) and aqueous acid

6) Propose a synthesis of 4-acetyl-2-nitrotoluene starting with toluene.


Name _____________________

Section ____________________

CHEM 238 B Quiz 2

Version B

7) Propose a synthesis of 2-bromo-4-tert-Butyltoluene starting with toluene. If an ortho, para mixture

is formed in any step of the reaction, assume that you can separate the two isomers.

8) Provide the reagents required at each step of the following reaction.

1) AlCl3

2) NBS




9) Draw the missing intermediate and product in the reaction below; where E+ is an electrophile.


the reaction above.

d) Same

e) Slow, Fast

f) Fast, Slow

11) For the pair of compounds given choose which one will react faster with the indicated reagent and

write a chemical equation for the faster reaction.

Methyl benzoate or phenyl acetate with bromine/FeBr3 in an inert solvent.

12) Draw the structure of allylbenzene:


Name _____________________

Section ____________________

CHEM 238 B Quiz 2

Version C

1) For the pair of compounds given choose which one will react faster with the indicated reagent and

write a chemical equation for the faster reaction.

Toluene or chlorobenzene with a mixture of nitric acid and sulfuric acid

2) Draw the missing intermediate and product in the reaction below.


the reaction above.

g) Same

h) Slow, Fast

i) Fast, Slow


Propose a synthesis of pure 2-bromotoluene starting with toluene. If an ortho, para mixture is

formed in any step of the reaction, this would not be a ‘pure’ product as required.

4) The following structure may be represented by at least one alternative resonance structure in which

all six-membered rings correspond to Kekulé forms of benzene. Write such a resonance structure

for:

5) Provide the reagents required at each step of the following reaction.

O

O

O O

Br

1 2

3 4

Cl

1) AlCl3

2) NBS




QUIZ #3.1 (Ch. 13-14) Name__________________________ Sec_______

(03) I. Provide unambiguous systematic names for the following organometallic compounds:

(07) II. For the compound shown below, predict the

1H and

13C NMR spectra, including peak multiplicities.

(03) III. J-coupling by alcohol protons (the OH) is observed when the 1H NMR spectrum is obtained using a polar aprotic

solvent (e.g., DMSO-d6) because intermolecular proton exchange is hindered by hydrogen bonding with the solvent.

Please explain: (a) How to distinguish primary and secondary alcohols from one another using this concept.

(b) The effect of treatment with excess D2O upon the alcohol proton resonances.

(02) IV. Circle the compound that contains a more polar metal carbon bond, and briefly explain why:


(12) V. Consider the following reaction used in the total synthesis of the natural product Asteltoxin. Intermediate (B)

illustrates an example of what is known as a [2,3] sigmatropic rearrangement, which you have not seen yet, though as a

budding intellectual you find utterly fascinating(!). Note reactions (1) and (2) are two distinct additions that are performed

in the same reaction flask (also recall that Ph = phenyl):

(a) Propose a synthesis of the starting material (A) from a vinyl halide and electrophile of your choice.

(b) Draw the principal organic products formed between (A) and n-butyl lithium in step (1) of the reaction.

(c) How many 13

C resonances would be observed in (A)? How about (C)? A:____3_____ C:____9______

(Compound (A) is symmetrical, (C) has symmetry only in the phenyl substituent) (2 pts each; 1 pt if 6 or 7 assigned to (C))

(d) Ignoring the phenylsulfoxide unit, how does the UV λmax change from (A)�� (C)? ___________________________

Acceptable responses: “redshift;” “increases from conjugation;” “goes above 231 nm;” suggests longer λmax (2 pts)

Also: C appears at lower energy (longer λmax ) due to greater conjugation OR <200 becomes 220 -235 nm

(03) VI. Perform a retrosynthetic analysis on the following target molecule (TGT), working back to the ketone shown; you

do not need to provide reagents, just the synthetic intermediates and a brief descriptor of the transform (i.e. “bromination”,

“formation of Grignard reagent”, “dehydrobromination”, “protonation of anionic product”, etc.):


QUIZ #3.2 (Ch. 13-14) Name__________________________ Sec_______


(07) II. For the compound shown below, predict the 1H and


methyl propionate

1H NMR 13C NMR

O

O(a) 4.0 ppm (3H, singlet)

(b) 2.2 ppm (2H, quartet)

(c) 1.0 ppm (3H, triplet)

(1 pt each; -1 for switching

signals; -1 for wrong mult.)

200-220 ppm (C=O)

60-90 ppm (OCH3)

20-50 ppm (CH3C=O)

0-40 ppm (CH2CH3)

(1 pt each; -1 if any multiplicities)

(a)

(b)

(c)




(b) The effect of treatment with excess D2O upon the alcohol proton resonances.

(SEE ABOVE)





budding intellectual you find utterly fascinating(!). Note reactions (1) and (2) are two distinct additions that are performed in

the same reaction flask (recall that Ph = phenyl):


(SEE ABOVE)


(SEE ABOVE)

(c) How many 13

C resonances would be observed in (A)? How about (C)? A:_________ C:__________




“formation of Grignard reagent”, “dehydrobromination”, “protonation of anionic product”, etc):

(SEE ABOVE)


QUIZ #3.3 (Ch. 13-14) Name__________________________ Sec_______


(07) II. For the compound shown below, predict the 1H and





(b) The effect of treatment with excess D2O upon the –CH2O– resonance of alcohol (CH3)2CHCH2OH.

(A) SEE ABOVE

(B) The observed doublet of doublets would become a doublet, since the O-H proton exchanges with 2D (NMR silent!)





budding intellectual you find utterly fascinating(!). Note reactions (1) and (2) are two distinct additions that are performed in

the same reaction flask (recall that Ph = phenyl):


(SEE ABOVE)


(SEE ABOVE)

(c) How many 13

C resonances would be observed in (A)? How about (C)? A:_________ C:__________




“formation of Grignard reagent”, “dehydrobromination”, “protonation of anionic product”, etc):

(SEE ABOVE)


QUIZ #4.1 (Ch. 15-16) Name_________________________ Sect_______

(05) I. Suggest appropriate starting materials for the series of reactions below, all of which lead to the alcohol shown.

(05) II. Predict the major organic product, including stereochemistry as needed, in the following reactions. Also provide

an unambiguous systematic name for the products.

(06) III. Outline a practical synthesis of isobutylbenzene (PhCH2CH(CH3)2) starting from benzene, isobutyl alcohol

(HOCH2CH(CH3)2) and any necessary organic and inorganic reagents.


(04) IV. Draw the principal organic product and an arrow-pushing mechanism for the reaction below.

(06) V. The following epoxidation strategy has been reported in the chemical literature.

(a) Propose a reasonable arrow-pushing mechanism. Note the numbered carbons in the substrate and product.

(b) Briefly comment on why this reaction was chosen to prepare this particular epoxide instead of using the

epoxidation reactions you have learned so far (e.g., mCPBA, or Br2/H2O then intramolecular SN2).

(04) VI. In the presence of thiophenol (PhSH) under strongly basic conditions, the 2,3-epoxy-1-ol below is converted in

high yield and regioselectivity to the 2,3-dihydroxy thioether product depicted. The mechanism of this hydroxyl transfer

reaction is known as the Payne Rearrangement. Show an arrow-pushing mechanism for this reaction (HINT: Start off by

deprotonating the alcohol in the starting material. ALSO: Use the product stereochemistry as a guide!!!!!!).


QUIZ #4.2 (Ch. 15-16) Name_________________________ Sect_______

(06) I. The following epoxidation strategy has been reported in the chemical literature.




(SEE ABOVE)

(05) II. Suggest appropriate starting materials for the series of reactions below, all of which lead to the alcohol shown.

(05) III. Predict the major organic product, including stereochemistry as needed, in the following reactions. Also provide



(06) IV. Outline a practical synthesis of isobutylbenzene (PhCH2CH(CH3)2) starting from benzene, isobutyl alcohol


(04) V. Draw the principal organic product and an arrow-pushing mechanism for the reaction below. Note the reactant is

a single enantiomer, so stereochemistry should be included in the product.





(SEE ABOVE)


QUIZ #4.3 (Ch. 15-16) Name_________________________ Sect_______

(05) I. Suggest appropriate starting materials for the series of reactions below, all of which lead to the alcohol shown.

(05) II. Predict the major organic product, including stereochemistry as needed, in the following reactions. Also provide


(06) III. The following epoxidation strategy has been reported in the chemical literature.




(SEE ABOVE)


(06) IV. Outline a practical synthesis of isobutylbenzene (PhCH2CH(CH3)2) starting from benzene, isobutyl alcohol


(04) V. Draw the principal organic product and an arrow-pushing mechanism for the reaction below.





(SEE ABOVE)

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