Chemistry 3720 Old Exams - hyperconjugation.com · Organic Chemistry Spectral Data Sheet Approximate 1H NMR Chemical Shifts (parts per million) R 3 C-H (alkyl) 0.9 to 1.8 R 3 N-C-H

Chemistry 3720 Old Exams

Practice Exams & Keys 2015-17

Spring 2017

Page File

3 Spring 2017 Exam 1

10 Spring 2017 Exam 1 Key





42 Spring 2017 Final (No Key)

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Chemistry 3720, Spring 2017 Exam 1 Student Name: “Y” Number:

This exam is worth 100 points out of a total of 700 points for Chemistry 3720/3720L. You have 50 minutes to

complete the exam. The spectroscopy sheet is attached as the last page. Good Luck!

1. (8 pts) Give a retrosynthetic plan for building the following molecule from the sources of carbon shown.

Then show your synthesis in the forward direction that would result in the alkyl bromide. You may assume

that you have access to all of the usual reagents in an organic lab.

2

2. (20 pts) Draw the expected major products from each step of the following reaction sequences. Make sure

you take into account any stereochemical changes where applicable.

3

3. (8 pts) The mass spectrum below belongs to one of the five compounds shown. Indicate which molecule

matches the spectrum and explain why you chose that one and not the other four. Atomic masses (in atomic

mass units, a.m.u.) are as follows: C = 12 ; H = 1 ; O = 16 ; F = 19 ; Cl = 35.45 ; Br = 79.90.

4. (8 pts) Draw a complete mechanism for the following ester to ether conversion.

4

5. (9 pts) For each of the following reactions, label the oxidation state of the highlighted carbon atoms in the

starting material and product. Then indicate whether the reaction is an oxidation, reduction or neither, and

give a reagent (above the arrow) that will accomplish the conversion.

6. (7 pts) IR spectrum A belongs to a starting material and B belongs to the product when A is reacted under

certain conditions. Of the reactions shown, which one matches the IR data give? Explain your choice.

5

7. (16 pts) In the boxes below, give the major product(s) from each step of the following sequence. The given

clues might help you to work out the answers. If no reaction is expected, write “NR” in the box.

8. (8 pts) For each of the following epoxide ring-opening reactions, explain in some detail the regioselectivity

and stereoselectivity observed. Discuss the different mechanisms operating.

6

9. (8 pts) The following attempted synthesis contains a fatal flaw that prevents it from actually working. What

is wrong here and how would you make it work? Show the steps and reagents required for your synthesis.

10. (8 pts) For each of the following molecules, indicate how many different signals you expect to see in the

proton (1H) NMR spectrum. Then label the approximate chemical shift (ppm) for the highlighted atoms.

Youngstown State University Organic Chemistry Spectral Data Sheet

Approximate 1H NMR Chemical Shifts (parts per million)

R3C-H (alkyl) 0.9 to 1.8 R3N-C-H (N neighbor) 2.2 to 2.9

C=C-C-H (allylic) 1.6 to 2.6 Cl-C-H (Cl neighbor) 3.1 to 4.1

O=C-C-H (alpha to C=O) 2.1 to 2.5 Br-C-H (Br neighbor) 2.7 to 4.1

NC-C-H (alpha to CN) 2.1 to 3.0 -O-C-H (O neighbor) 3.3 to 3.7

C C H (alkyne) 2.5 R2N-H (amine) 1 to 3

Ar-C-H (benzylic) 2.3 to 2.8 RO-H (alcohol) 0.5 to 5

C=C-H (alkene) 4.5 to 6.5 Ar-O-H (phenol) 6 to 8

Ar-H (benzene) 6.5 to 8.5 -CO2H (carboxylic acid) 10 to 13

O=C-H (aldehyde) 9 to 10

Approximate 13C NMR Chemical Shifts (parts per million)

RCH3 (alkyl) 0 to 35 RCH2Br (alkyl bromide) 20 to 40

R2CH2 (alkyl) 15 to 40 RCH2Cl (alkyl chloride) 25 to 50

R3CH (alkyl) 25 to 50 RCH2NH2 (alkyl amine) 35 to 50

R4C (alkyl) 30 to 40 RCH2OR (alcohol or ether) 50 to 65

R-CC-R (alkyne) 65 to 90 RCN (nitrile) 110 to 125

R2C=CR2 (alkene) 100 to 150 RCO2R (acid, ester) 160 to 185

Benzene C (aromatic) 110 to 175 RCHO, R2CO (ald’hyde, ketone) 190 to 220

Approximate IR Absorption Frequencies (cm-1)

Stretching Vibrations

-O-H (alcohol) 3200 to 3600 C=C (alkenes) 1620 to 1680

-O-H (carbox. acid) 2500 to 3600 C=O (ald., ketones) 1710 to 1750

R2N-H (amine) 3350 to 3500 C=O (acyl halides) 1770 to 1815

sp C-H (alkynes) 3310 to 3320 C=O (esters) 1730 to 1750

sp2 C-H (alkenes) 3000 to 3100 C=O (amides) 1680 to 1700

sp3 C-H (alkanes) 2850 to 2950

sp2 C-O (carbonyls) 1200 triple bond (alkynes) 2100 to 2200

sp3 C-O (alcoh., ethers) 1025 to 1200 triple bond (nitriles) 2240 to 2280

Bending Vibrations

RCH=CH2 (alkenes) 910, 990 Monosubstit’d benzene 730 to 770, 690 to 710

R2C=CH2 (alkenes) 890 ortho-disubstit’d benzene 735 to 770

R2C=CHR’ (alkenes) 790 to 840 meta-disubstit’d benzene 750 to 810, 680 to 730

para-disubstituted benzene 790 to 840

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Chemistry 3720, Spring 2017 Exam 1 – Key Student Name: “Y” Number:



1. (8 pts) Give a retrosynthetic plan for building the following molecule from the sources of carbon shown.

Then show your synthesis in the forward direction that would result in the alkyl bromide. You may assume

that you have access to all of the usual reagents in an organic lab.

2



3

3. (8 pts) The mass spectrum below belongs to one of the five compounds shown. Indicate which molecule

matches the spectrum and explain why you chose that one and not the other four. Atomic masses (in atomic



4

5. (9 pts) For each of the following reactions, label the oxidation state of the highlighted carbon atoms in the

starting material and product. Then indicate whether the reaction is an oxidation, reduction or neither, and

give a reagent (above the arrow) that will accomplish the conversion.

6. (7 pts) IR spectrum A belongs to a starting material and B belongs to the product when A is reacted under

certain conditions. Of the reactions shown, which one matches the IR data give? Explain your choice.

5


clues might help you to work out the answers. If no reaction is expected, write “NR” in the box.

8. (8 pts) For each of the following epoxide ring-opening reactions, explain in some detail the regioselectivity

and stereoselectivity observed. Discuss the different mechanisms operating.

6

9. (8 pts) The following attempted synthesis contains a fatal flaw that prevents it from actually working. What

is wrong here and how would you make it work? Show the steps and reagents required for your synthesis.

10. (8 pts) For each of the following molecules, indicate how many different signals you expect to see in the

proton (1H) NMR spectrum. Then label the approximate chemical shift (ppm) for the highlighted atoms.

1




#Pi bonds and/or Cycles = [#C - (#H/2) - (#X/2) + #N/2] +1

1. (8 pts) Provide the major product(s) expected to be formed under the following conditions and then draw a

detailed mechanism for the process that includes all important resonance structures where applicable. Why

is there only one major product formed here?

2


you take into account any regiochemical issues where applicable.

3

3. (9 pts) For each of the following molecules, draw a Frost circle and populate the molecular orbitals with the

appropriate number of electrons. Then apply Hückel’s rule to each system and indicate which molecule(s)

is/are aromatic. Give a few words of explanation for your choices.

4. (8 pts) Draw the major final product expected from each of the following reactions:

4

5. (18 pts) A new anti-cancer compound has been isolated from a microorganism and is found, from the mass

spectrum, to have the formula C12H14O2 and M+ of 190 atomic mass units. The infra-red spectrum has

signals at 3500, 1740, 740 and 700 wavenumbers and the proton and carbon spectra are given below.

Provide the structure of the unknown and then indicate which signals belong to which atoms in the 1H

NMR spectrum.

1H NMR (ppm): 0.86 (d, 6H, J = 7.0 Hz); 2.38 (octet, 1H, J = 7.0 Hz); 5.63 (dd, 1H, J = 12.0, 7.0 Hz);

6.35 (d, 1H, J = 12.0 Hz); 7.55 (d, 2H, J = 8.0 Hz); 7.83 (d, 2H, J = 8.0 Hz); 12.71 (s, 1H).

13

C NMR (ppm): 22.6 (q); 28.0 (d); 127.7 (d); 129.0 (d); 129.4 (s); 130.2 (d); 141.6 (s); 142.4 (d); 169.3 (s).

5

6. (8 pts) Provide the major product that you expected to be formed under the following conditions. Then draw

a complete mechanism, including all important resonance structures, for the product’s formation. Explain,

briefly, why this particular product is major.

7. (7 pts) The 13

C spectrum below belongs to one of the five molecules given. Indicate which one you think

matches the NMR data and explain your choice by pointing out which signal matches which carbon(s) and

how the coupling data helped inform your decision.

13

C NMR (ppm): 23.3 (q); 33.2 (d); 126.6 (d); 129.6 (d); 134.1 (s); 154.2 (s); 191.0 (d).

6

8. (6 pts) Provide the major product that you would expect to be formed under each of the following reaction

conditions. Then explain the outcomes by discussing the effect of temperature on the reaction pathway.

9. (16 pts) In the boxes provided, draw the expected major product from each step in the following synthetic

scheme. Use the clues as needed and be careful if/when stereochemistry/regiochemistry is an issue.






























Bending Vibrations





1

Chemistry 3720, Spring 2017 Exam 2 - Key Student Name: “Y” Number:





detailed mechanism for the process that includes all important resonance structures where applicable. Why is

there only one major product formed here?

2


you take into account any regiochemical issues where applicable.

3

3. (9 pts) For each of the following molecules, draw a Frost circle and populate the molecular orbitals with the

appropriate number of electrons. Then apply Hückel’s rule to each system and indicate which molecule(s)

is/are aromatic. Give a few words of explanation for your choices.

4. (8 pts) Draw the major final product expected from each of the following reactions:

4

5. (18 pts) A new anti-cancer compound has been isolated from a microorganism and is found, from the mass

spectrum, to have the formula C12H14O2 and M+ of 190 atomic mass units. The infra-red spectrum has signals

at 3500, 1740, 740 and 700 wavenumbers and the proton and carbon spectra are given below. Provide the

structure of the unknown and then indicate which signals belong to which atoms in the 1H NMR spectrum.

1H NMR (ppm): 0.86 (d, 6H, J = 7.0 Hz); 2.38 (octet, 1H, J = 7.0 Hz); 5.63 (dd, 1H, J = 12.0, 7.0 Hz);

6.35 (d, 1H, J = 12.0 Hz); 7.55 (d, 2H, J = 8.0 Hz); 7.83 (d, 2H, J = 8.0 Hz); 12.71 (s, 1H).

13C NMR (ppm): 22.6 (q); 28.0 (d); 127.7 (d); 129.0 (d); 129.4 (s); 130.2 (d); 141.6 (s); 142.4 (d); 169.3 (s).

5

6. (8 pts) Provide the major product that you expected to be formed under the following conditions. Then draw

a complete mechanism, including all important resonance structures, for the product’s formation. Explain,

briefly, why this particular product is major.

7. (7 pts) The 13C spectrum below belongs to one of the five molecules given. Indicate which one you think

matches the NMR data and explain your choice by pointing out which signal matches which carbon(s) and

how the coupling data helped inform your decision.

13C NMR (ppm): 23.3 (q); 33.2 (d); 126.6 (d); 129.6 (d); 134.1 (s); 154.2 (s); 191.0 (d).

6

8. (6 pts) Provide the major product that you would expect to be formed under each of the following reaction

conditions. Then explain the outcomes by discussing the effect of temperature on the reaction pathway.


scheme. Use the clues as needed and be careful if/when stereochemistry/regiochemistry is an issue.

1




HDI/Unsaturation Number = [#C atoms – ½#H atoms – ½#Halogen atoms + ½#N atoms] + 1

1. (8 pts) Give a detailed mechanism for each step in the following conversion of a ketone to a dithioacetal

that includes any important resonance structures for intermediates that are formed. Label each step in terms

of what kind of event is happening (proton transfer, nucleophilic attack, etc.).

2

2. (10 pts) Draw a detailed reaction mechanism for the following nitrile hydrolysis that includes resonance

structures for the intermediates that are formed. Label each step in terms of what kind of event is occurring

(proton transfer, nucleophilic attack, etc.).

3. (8 pts) Draw a complete reaction mechanism for the following ester saponification process. Label each

step in terms of what kind of event is happening (proton transfer, nucleophilic attack, etc.).

3

4. (20 pts) Provide the expected major products from each step of the following reaction sequences. Be

careful if any stereochemical and/or regiochemical issues arise.

4

5. (8 pts) Give the expected major and minor products from the following reaction sequence as well as a

detailed mechanism, which includes all resonance structures for intermediate(s) for the formation of both

major and minor isomers. Explain briefly the regiochemical distribution of products.

6. (8 pts) Provide a complete mechanism for the following Baeyer-Villager ketone oxidation and then explain

the regiochemical outcome. What evidence is given in the product structure to help you decide whether the

migration process is step-wise or concerted?

5

7. (16 pts) In the boxes below, provide the major product(s) from each step of the following sequence. Using

the spectroscopic and molecular formula clues might help you to come up with answers.

8. (8 pts) Make the following molecule from the compounds given on the right. You have access to all of the

usual reagents found in an organic lab and you do not need to show retrosynthesis unless it helps.

6

9. (7 pts) Draw a complete mechanism for the following crossed-aldol synthesis that describes how the final

product is formed. Also include any important resonance structures for intermediates that are formed.

10. (7 pts) Provide a complete step-by-step mechanism for the following acetal hydrolysis that includes any

important resonance structures for intermediates that are formed. Label what is happening in each step.






























Bending Vibrations





1





1. (8 pts) Give a detailed mechanism for each step in the following conversion of a ketone to a dithioacetal

that includes any important resonance structures for intermediates that are formed. Label each step in terms

of what kind of event is happening (proton transfer, nucleophilic attack, etc.).

2

2. (10 pts) Draw a detailed reaction mechanism for the following nitrile hydrolysis that includes resonance

structures for the intermediates that are formed. Label each step in terms of what kind of event is occurring

(proton transfer, nucleophilic attack, etc.).

3. (8 pts) Draw a complete reaction mechanism for the following ester saponification process. Label each

step in terms of what kind of event is happening (proton transfer, nucleophilic attack, etc.).

3

4. (20 pts) Provide the expected major products from each step of the following reaction sequences. Be

careful if any stereochemical and/or regiochemical issues arise.

4

5. (8 pts) Give the expected major and minor products from the following reaction sequence as well as a

detailed mechanism, which includes all resonance structures for intermediate(s) for the formation of both

major and minor isomers. Explain briefly the regiochemical distribution of products.

6. (8 pts) Provide a complete mechanism for the following Baeyer-Villager ketone oxidation and then explain

the regiochemical outcome. What evidence is given in the product structure to help you decide whether the

migration process is step-wise or concerted?

5

7. (16 pts) In the boxes below, provide the major product(s) from each step of the following sequence. Using


8. (8 pts) Make the following molecule from the compounds given on the right. You have access to all of the

usual reagents found in an organic lab and you do not need to show retrosynthesis unless it helps.

6

9. (7 pts) Draw a complete mechanism for the following crossed-aldol synthesis that describes how the final

product is formed. Also include any important resonance structures for intermediates that are formed.

10. (7 pts) Provide a complete step-by-step mechanism for the following acetal hydrolysis that includes any

important resonance structures for intermediates that are formed. Label what is happening in each step.

1

Chemistry 3720, Spring 2017 Final Exam Student Name: “Y” Number:




1. (9 pts) For the following Michael addition, give a complete mechanism, including resonance structures, for

the conversion of the enamine into the final product. Explain the observed regioselectivity.

2

2. (9 pts) Provide a detailed mechanism for the following tropane alkaloid synthesis that includes resonance

structures for any intermediates that are formed. Label what type of event is happening in each step.

3. (9 pts) Draw a complete mechanism for the following ether synthesis that includes all important resonance

structures for intermediates that are formed.

3

4. (9 pts) Provide a detailed mechanism for the following Gabriel amine synthesis that includes important

resonance structures for intermediates that are formed.

5. (8 pts) Give a mechanistic interpretation (push arrows) to show how the enantiomerically pure epoxide is

converted to the racemic mxture of products. Include resonance structures for any intermediates formed.

4

6. (20 pts) Provide the expected major products from each step of the following synthetic sequences. Be

sure to take any stereochemical and regiochemical changes into consideration where applicable.

5

7. (14 pts) In the boxes below, provide the major product from each step of the following sequence. Using


8. (8 pts) Provide a retrosynthesis for the following molecule that goes back to the given starting materials.

Then, using any of the reactions and reagents encountered in Chemistry 3719/3720, build the molecule.

6

9. (14 pts) For the following multi-step biodegradation of amino acids, insert each of the curved arrows

needed to describe each bond-making and bond-breaking process. Also label what is happening in each

step (proton transfer, nucleophilic attack, etc.). Note: “Enz” = the enzyme that mediates the process.

7

10. (12 pts) Provide the major product from each step of the following reaction sequence. Be careful when

regiochemistry is an issue.

11. (10 pts) When attempted, the synthesis below fails to give the indicated product. Explain what the problem

is here and then provide a route that will be successful. Include structures of intermediate products.

8

12. (16 pts) A newly isolated organic compound has the molecular formula C13H16O2; the mass spectrum shows

M+ = 204.12 a.m.u., the IR spectrum shows significant signals at 1740, 1200, and 810 cm-1

, and the 1H and

13C NMR spectra are given below. Suggest a structure for the unknown molecule that matches the data and

then indicate which signals belong to which protons in the 1H NMR spectrum.

1H NMR (CDCl3) ppm : 1.01 (t, 3H, J = 7.0 Hz); 1.73 (sextet, 2H, J = 7.0 Hz); 2.41 (s, 3H); 4.12 (t, 2H, J = 7.0

Hz); 6.31 (d, 1H, J = 16.0 Hz); 7.39 (d, 1H, J = 8.0 Hz); 7.48 (d, 1H, J = 16.0 Hz); 7.59 (d, 1H, J = 8.0 Hz)

13

C NMR (CDCl3) ppm : 10.3 (q); 21.3 (q); 22.0 (t); 67.5 (t); 116.2 (d); 128.5 (d, double intensity); 128.9

(d, double intensity); 132.2 (s); 137.6 (s); 145.1 (d); 166.5 (s)

9

13. (12 pts) Provide a detailed reaction mechanism for the following process that includes all resonance

structures for any intermediates that are formed.

14. (12 pts) Draw a detailed mechanism for the following reaction sequence that includes resonance structures

for intermediates. Label what is happening in each step (proton transfer, nucleophilic attack, etc.).

10

15. (9 pts) Provide a detailed mechanism for the following iodoform reaction that explains the formation of

the two products. Make sure to include resonance structures for intermediates.

16. (10 pts) From the molecules shown below, choose the one that one matches the given mass spectrum.

Then explain your choice and draw the structure of the fragment that corresponds to the base peak.

Atomic masses (in a.m.u.) are as follows: C = 12 ; H = 1 ; O = 16 ; F = 19 ; Cl = 35.45 ; Br = 79.90.

11

17. (10 pts) The following reaction results in two products that are formed in equal amounts. Give those

products as well as a detailed mechanism that describes how they are formed.

18. (9 pts) For each of the following polymers, circle the repeating unit and give starting materials that could

be used to synthesize the material. Indicate if each polymer is formed by addition or condensation.






























Bending Vibrations





Spring 2016

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1. (8 pts) Give the major products from each step of the reaction sequences below and then show whether the

highlighted carbon atoms have been oxidized, reduced or unchanged in each step by assigning each an

oxidation number.

2



3

3. (9 pts) The following ketone synthesis is impossible to complete under the given conditions. Explain why

and give reagents that would allow for access to the ketone. Include structures of intermediate products.


4

5. (7 pts) The mass spectrum below belongs to one of the four compounds shown. Indicate which molecule the

spectrum belongs to and explain why you chose that one and not the other three. Atomic masses (in atomic


6. (7 pts) Which of the following molecules matches this IR spectrum? Point out important signals that helped

you to decide on your choice and why the spectrum does not match the other possibilities.

5


spectroscopic and molecular formula clues might help you to work out the answers.

8. (9 pts) Draw the structures of each of the following molecules and then provide the reagents needed to

convert each of the given starting materials into the required product.

6

9. (8 pts) Within each of the following pairs of molecules circle the one required for the answer and give a few

words of explanation for your choice.

10. (8 pts) Provide a suitable organic compound that would serve as a precursor (starting material) for each of

the following molecules under the given conditions.






























Bending Vibrations





1




1. (8 pts) Give the major products from each step of the reaction sequences below and then show whether the

highlighted carbon atoms have been oxidized or reduced in each step by assigning each an oxidation

number.

2



3

3. (9 pts) The following ketone synthesis is impossible to complete under the given conditions. Explain why

and give reagents that would allow for access to the ketone. Include structures of intermediate products.


4

5. (7 pts) The mass spectrum below belongs to one of the four compounds shown. Indicate which molecule the

spectrum belongs to and explain why you chose that one and not the other three. Atomic masses (in atomic


6. (7 pts) Which of the following molecules matches this IR spectrum? Point out important signals that helped

you to decide on your choice and why the spectrum does not match the other possibilities.

The strong signal at ~1720 cm

-1 indicates a carbonyl which a) and b) don’t have; d) would need an OH at 3300-3600 cm

-1.

5


spectroscopic and molecular formula clues might help you to work out the answers.

8. (9 pts) Draw the structures of each of the following molecules and then provide the reagents needed to

convert each of the given starting materials into the required product.

6

9. (8 pts) Within each of the following pairs of molecules circle the one required for the answer and give a few

words of explanation for your choice.

10. (8 pts) Provide a suitable organic compound that would serve as a precursor (starting material) for each of

the following molecules under the given conditions.

1






detailed mechanism for the process that includes all important resonance structures where applicable.

2



3

3. (9 pts) In the following experiments a diene is reacted with a dienophile at high temperature. Decide which

reactions will give a cycloaddition product and which will not. For those that do, draw the structure of the

major cycloadduct; for those that do not, give a brief explanation.

4. (8 pts) For the following molecular orbital diagrams used in describing the interactions of reactants in the

Diels-Alder reaction, shade in the orbitals as needed to describe the orbital interactions at each energy

level. Then populate each set of orbitals with the appropriate number of electrons and indicate in each

reactant which orbital is the highest occupied M.O. and which is the lowest unoccupied M.O.

4

5. (18 pts) An unknown organic molecule has been isolated from a tropical plant and is found, from the mass

spectrum, to have the formula C12H13NO and M+ of 187 atomic mass units. The infra-red spectrum has

signals at 2250, 1720, 760, and 690 wavenumbers and the proton and carbon spectra are given below.


NMR spectrum.

1H NMR (ppm): 1.18 (t, 3H, J = 7.0 Hz); 2.60 (t, 2H, J = 6.9 Hz); 2.72 (q, 2H, J = 7.0 Hz); 2.92 (t, 2H, J = 6.9 Hz);

7.32 (t, 1H, J = 6.8 Hz); 7.39 (d, 1H, J = 6.8 Hz); 7.79 (s, 1H); 7.93 (d, 1H, J = 6.8 Hz).

13

C NMR (ppm): 11.8 (t); 14.5 (q); 28.2 (t); 34.3 (t); 119.2 (s); 126.0 (d); 127.7 (d); 128.5 (d);

132.1 (d); 136.6 (s); 144.6 (s); 200.1 (s).

5

6. (8 pts) Provide a complete mechanism for the following Friedel-Crafts alkylation that includes resonance

structures for the sigma complex that is formed as an intermediate.

7. (7 pts) The proton spectrum below belongs to one of the five molecules given. Indicate which one you

think matches the NMR data and explain your choice by pointing out which signal matches which

proton(s) and how the coupling constant data helped inform your decision.

1H NMR (ppm): 1.05 (s, 9H); 1.21 (t, 3H, J = 7.0 Hz); 4.06 (q, 2H, J = 7.0 Hz);

5.85 (d, 1H, J = 16 Hz); 6.88 (d, 1H, J = 16 Hz).

6

8. (6 pts) Treatment of the following diene with HBr above room temperature leads to two addition products,

one of which is major. Draw the two products and a mechanism for their formation; then explain briefly

the isomer distribution observed at this temperature.

9. (6 pts) Benzene is aromatic but cyclobutadiene is antiaromatic. Draw Frost circles for each molecule and

use them to explain briefly why benzene is so stable and cyclobutadiene is so unstable.


scheme.






























Bending Vibrations





1






detailed mechanism for the process that includes all important resonance structures where applicable.

2



3

3. (9 pts) In the following experiments a diene is reacted with a dienophile at high temperature. Decide which

reactions will give a cycloaddition product and which will not. For those that do, draw the structure of the

major cycloadduct; for those that do not, give a brief explanation.

4. (8 pts) For the following molecular orbital diagrams used in describing the interactions of reactants in the

Diels-Alder reaction, shade in the orbitals as needed to describe the orbital interactions at each energy

level. Then populate each set of orbitals with the appropriate number of electrons and indicate in each

reactant which orbital is the highest occupied M.O. and which is the lowest unoccupied M.O.

4

5. (18 pts) An unknown organic molecule has been isolated from a tropical plant and is found, from the mass

spectrum, to have the formula C12H13NO and M+ of 187 atomic mass units. The infra-red spectrum has

signals at 2250, 1720, 760, and 690 wavenumbers and the proton and carbon spectra are given below.


NMR spectrum.

1H NMR (ppm): 1.18 (t, 3H, J = 7.0 Hz); 2.60 (t, 2H, J = 6.9 Hz); 2.72 (q, 2H, J = 7.0 Hz); 2.92 (t, 2H, J = 6.9 Hz);

7.32 (t, 1H, J = 6.8 Hz); 7.39 (d, 1H, J = 6.8 Hz); 7.79 (s, 1H); 7.93 (d, 1H, J = 6.8 Hz).

13

C NMR (ppm): 11.8 (t); 14.5 (q); 28.2 (t); 34.3 (t); 119.2 (s); 126.0 (d); 127.7 (d); 128.5 (d);

132.1 (d); 136.6 (s); 144.6 (s); 200.1 (s).

5

6. (8 pts) Provide a complete mechanism for the following Friedel-Crafts alkylation that includes resonance

structures for the sigma complex that is formed as an intermediate.

7. (7 pts) The proton spectrum below belongs to one of the five molecules given. Indicate which one you

think matches the NMR data and explain your choice by pointing out which signal matches which

proton(s) and how the coupling constant data helped inform your decision.

1H NMR (ppm): 1.05 (s, 9H); 1.21 (t, 3H, J = 7.0 Hz); 4.06 (q, 2H, J = 7.0 Hz);

5.85 (d, 1H, J = 16 Hz); 6.88 (d, 1H, J = 16 Hz).

The 16 Hz coupling constant matches the trans alkene.

6

8. (6 pts) Treatment of the following diene with HBr above room temperature leads to two addition products,

one of which is major. Draw the two products and a mechanism for their formation; then explain briefly

the isomer distribution observed at this temperature.

The 1,4-adduct is favored here because the higher temperature allows for the additions to be reversible. This will allow for an equilibrium favoring the more stable alkene, i.e. the 1,4-isomer.

9. (6 pts) Benzene is aromatic but cyclobutadiene is antiaromatic. Draw Frost circles for each molecule and

use them to explain briefly why benzene is so stable and cyclobutadiene is so unstable.

All of the available electrons in the benzene case go into bonding orbitals and so stabilize this molecule whereas the second pair of electrons in cyclobutadiene have to be split into two separate non-bonding orbitals thereby destabilizing the

molecule and making it anti-aromatic.


scheme.

1






detailed mechanism for the process.

2



3


scheme.

4. (8 pts) Provide a product and a complete mechanism for the following reaction that includes resonance

structures for the charged complex that is formed as an intermediate.

4

5. (10 pts) An efficient synthesis of the following molecule is not as straightforward as it might appear. Explain

why and then give the reagents required to make the molecule in high yield starting from benzene. Give the

structures of all intermediate products in your synthesis.

6. (8 pts) Provide the reagents and conditions needed to convert each starting material into the given product.

More than one set of reagents may be required in each case.

5

7. (8 pts) In the following reaction two regioisomeric bromides are produced as shown. Decide which product

is major, then give a mechanism for its formation, including all important resonance structures. Finally,

explain briefly the regioselectivity observed.

8. (8 pts) Provide a mechanism for the following lactone formation that includes all of the important resonance

structures for any intermediates that are formed. Explain briefly the role of anhydrous MgSO4 in this process.

6

9. (8 pts) Produce a retrosynthetic analysis for the following molecule that goes back to 1-butanol as the only

source of carbon. Then give a synthesis of the molecule that includes structures of any intermediate products

that are formed on the way. Assume you have access to any reagents required and that mixtures are separable.

10. (8 pts) In the boxes provided, draw an appropriate starting material that would provide the given products

under the conditions shown.






























Bending Vibrations





1






detailed mechanism for the process.

2



3


scheme.

4. (8 pts) Provide a product and a complete mechanism for the following reaction that includes resonance

structures for the charged complex that is formed as an intermediate.

4

5. (10 pts) An efficient synthesis of the following molecule is not as straightforward as it might appear. Explain

why and then give the reagents required to make the molecule in high yield starting from benzene. Give the

structures of all intermediate products in your synthesis.

6. (8 pts) Provide the reagents and conditions needed to convert each starting material into the given product.

More than one set of reagents may be required in each case.

5

7. (8 pts) In the following reaction two regioisomeric bromides are produced as shown. Decide which product

is major, then give a mechanism for its formation, including all important resonance structures. Finally,

explain briefly the regioselectivity observed.

8. (8 pts) Provide a mechanism for the following lactone formation that includes all of the important resonance

structures for any intermediates that are formed. Explain briefly the role of anhydrous MgSO4 in this process.

6

9. (8 pts) Produce a retrosynthetic analysis for the following molecule that goes back to 1-butanol as the only

source of carbon. Then give a synthesis of the molecule that includes structures of any intermediate products

that are formed on the way. Assume you have access to any reagents required and that mixtures are separable.

10. (8 pts) In the boxes provided, draw an appropriate starting material that would provide the given products

under the conditions shown.

1


This exam is worth 200 points out of a total of 700 points for Chemistry 3720/3720L. You have 120 minutes to complete the exam. The spectroscopy sheet is attached as the last page. Good Luck!

HDI/Unsaturation Number = [#C atoms – ½#H atoms – ½#Halogen atoms + ½#N atoms] + 1 1. (9 pts) For the following Baeyer-Villager reaction, give a complete mechanism, including any resonance

structures, for the conversion of the ketone into the final product. Explain the observed regioselectivity.

2

2. (9 pts) Provide a detailed mechanism for the following Wittig synthesis that includes resonance structures for any intermediates that are formed.

3.

BrH3C

CH31. PPh3, ether

2. LDA, THF

H3C CH3

O

3. (9 pts) Draw a complete mechanism for the following Gabriel amine synthesis that includes any resonance

structures for intermediates that are formed.

3

4. (10 pts) Provide a detailed mechanism for the following Robinson synthesis that includes all important resonance structures for intermediates that are formed. Use “R” groups for brevity where possible.

5. (8 pts) Give the two major products that are formed from the following crown ether under the conditions provided and then a detailed mechanism for their formation.

4

6. (20 pts) Provide the expected major products from each step of the following reaction sequences. Be sure to take tautomerism into consideration where applicable.

5

7. (14 pts) In the boxes below, provide the major product from each step of the following sequence. Using the spectroscopic and molecular formula clues might help you to come up with answers.

8. (8 pts) One of the most common organic polymers used in 3D printing is polylactic acid (PLA), which is

derived from corn and is biodegradable. Provide a detailed mechanism, including any important resonance structures for how the two lactic acid units shown below come together to give the polymer linkage.

6

9. (15 pts) For the following multi-step laboratory synthesis of the amino acid (+/-)-proline, provide detailed mechanisms, including important resonance structures, for steps A, C, E, F and G.

O

OEt

O

EtO

CN

NaOEt

O

OEt

O

EtO

CN

O

OEt

O

EtO

NH2

Ni/H2HN

O

CO2Et

NH3 CO2H

H3O+,

Cl

ClHN

O

CO2Et

ClSOCl2 i. HO

ii. HCl NH2

CO2Hi. HO

NH

CO2

A B C

D E F G

(- EtOH)

(- CO2)

7

10. (12 pts) Provide a retrosynthesis for this molecule that goes back to 1-butanol as the only source of carbon. Then build the molecule in the forward direction showing the product from each step.

11. (10 pts) The 1H spectrum below belongs to one of the five molecules given. Indicate which one you think

matches the NMR data and explain your choice by pointing out which signal matches which proton(s).

O

OO

O

O

012345678PPM

1H NMR (ppm): 0.98 (d, 6H, J = 7.0 Hz); 1.18 (t, 3H, J = 6.9 Hz); 2.21 (multiplet, 1H, J = 7.0 Hz);

2.72 (q, 2H, J = 6.9 Hz); 2.88 (d, 2H, J = 7.0 Hz); 6.80 (d, 2H, J = 6.8 Hz); 6.90 (s, 2H, J = 6.8 Hz).

8

12. (12 pts) For each of the following series of molecules, circle the one that is asked for, then give a brief explanation for your choices.

13. (8 pts) Give the major product(s) expected to be formed under the following conditions, and then draw a

detailed mechanism that includes any important resonance structures. Why is/are your product(s) major?

9

14. (16 pts) An unknown organic compound has the molecular formula C11H14O3; the mass spectrum shows M+ = 194.09 a.m.u., the IR spectrum shows significant signals at 1740, 1200, and 800 cm-1, and the 1H and 13C NMR spectra are given below. Suggest a structure for the unknown molecule that matches the data and then indicate which signals belong to which protons in the 1H NMR spectrum.

0123456789PPM

1H NMR (CDCl3) ppm : 1.01 (t, 3H, J = 7.1 Hz), 1.91 (sextet, 2H, J = 7.1 Hz), 3.81 (singlet, 3H),

4.30 (t, 2H, J = 7.1 Hz), 6.85 (d, 2H, J = 6.8 Hz), 7.94 (d, 2H, J = 6.8 Hz).

020406080100120140160180PPM

13C NMR (CDCl3) ppm : 10.3 (q), 21.9 (t), 55.8 (q), 68.8 (t), 114.2 (d), 122.4 (s), 130.9 (d), 164.9 (s), 165.9 (s)

10

15. (8 pts) Indicate which product will be major, then give a detailed mechanism for its formation that includes resonance structures for any intermediates that are formed. Why is that product major?

16. (10 pts) Give a complete mechanism for this process that includes any important resonance structures.

11

17. (12 pts) Give the products from each step of the following synthetic sequence and then, on the NMR axis given below, draw the expected 1H spectrum of the final product.

18. (10 pts) The following molecule is lactose, which is found in milk, and is made up of one galactose and one glucose subunit. When this molecule is treated with H+/H2O it is hydrolyzed to the two individual monosaccharides. Draw structures of the D-galactose and D-glucose products and a mechanism for their formation, including any important resonance structures.

Spring 2015

Page File








1


This exam is worth 100 points out of a total of 700 points for Chemistry 3720/3720L. You have 50 minutes to complete the exam. The spectroscopy sheet is attached at the back of the exam. Good Luck!

1. (8 pts) Provide the product(s) expected from each step of the following reaction sequence as well as detailed mechanisms for each step in the conversion of starting materials to product(s).

2

2. (20 pts) Provide the expected major products from each step of the following reaction sequences. Be sure to include any stereochemical changes where applicable.

1. m-CPBA, CH2Cl2

2. CH3MgBr, ether

3. H3O+ (quench)

1. NaBH4, CH3OH

1. PCC, CH2Cl2

a.

b.

c.

d.

e.

2. NaH, THF

3. CH3Br

2. H3O+ (quench)

3. (C4H9)4N+ F-

2. TsCl, pyridine3. KOtBu, THF

2. PhMgBr, THF

3. NH4Cl (aq)

1. xs CH3MgBr, ether

O

O

CH3

OH 1. PDC, CH2Cl2

O

OMe

OSiMe3

OH

OHMe

3

3. (9 pts) Give the products expected to be formed from each step under the following conditions. Then draw complete mechanisms for each of the conversions.

4. (8 pts) From the molecules shown below, choose which one matches the following mass spectrum. Then

explain your choice, including reasons for why you didn’t pick the other possible answers. Atomic masses (in atomic mass units, a.m.u.) are as follows: C = 12 ; H = 1 ; O = 16 ; F = 19 ; Cl = 35.45 ; Br = 79.90.

a) b) c)Br

CH3

d)

Cl

CH3

F

CH3

OH

CH3

4

5. (14 pts) In the boxes below, provide the product(s) from each step of the following sequence. Using the spectroscopic and molecular formula clues might help you come up with answers.

6. (8 pts) Give the major product(s) expected to be formed under the following conditions as well as a

complete mechanism for its/their formation.

5

7. (8 pts) Give the expected product(s) from each step of the following reaction sequence, and then provide a mechanism for each synthetic step.

8. (8 pts) Provide a retrosynthesis for the following ether that goes back to the sources of carbon shown. Then show how you would make the target molecule using any of the reactions seen so far in Chemistry 3719/ 3720. Include a product from each of your synthetic steps.

6

9. (9 pts) Which of the following molecules does the IR spectrum below match? Explain your choice here by pointing out important signals that helped you to decide on your choice and why the spectrum does not match the other possibilities (Use the spectroscopy sheet for numbers).

10. (8 pts) For the following multi-step synthesis, give the product expected from each step as well as complete

mechanisms that describe all of the major events on the way from starting material to the final product.


Approximate 1H NMR Chemical Shifts (δ, ppm)

R3C-H (alkyl) 0.9-1.8 R3N-C-H (N neighbor) 2.2-2.9 C=C-C-H (allylic) 1.6-2.6 Cl-C-H (Cl neighbor) 3.1-4.1

O=C-C-H (α to C=O) 2.1-2.5 Br-C-H (Br neighbor) 2.7-4.1

NC-C-H (α to CN) 2.1-3.0 -O-C-H (O neighbor) 3.3-3.7

C C H (alkyne) 2.5 R2N-H (amine) 1-3 Ar-C-H (benzylic) 2.3-2.8 RO-H (alcohol) 0.5-5 C=C-H (alkene) 4.5-6.5 Ar-O-H (phenol) 6-8 Ar-H (benzene) 6.5-8.5 -CO2H (carboxylic acid) 10-13 O=C-H (aldehyde) 9-10

Approximate 13

C NMR Chemical Shifts (δ, ppm) RCH3 (alkyl) 0-35 RCH2Br (alkyl bromide) 20-40 R2CH2 (alkyl) 15-40 RCH2Cl (alkyl chloride) 25-50 R3CH (alkyl) 25-50 RCH2NH2 (alkyl amine) 35-50 R4C (alkyl) 30-40 RCH2OR (alcohol or ether) 50-65

C CR R (alkyne) 65-90 RCN (nitrile) 110-125 R2C=CR2 (alkene) 100-150 RCO2R (acid, ester) 160-185 Benzene C (aromatic) 110-175 RCHO, R2CO (aldehyde, ketone) 190-220 Approximate IR Absorption Frequencies (cm

-1)

Stretching Vibrations -O-H (alcohol) 3200-3600 C=C (alkenes) 1620-1680 -O-H (carbox. acid) 2500-3600 C=O (ald., ketones) 1710-1750 R2N-H (amine) 3350-3500 C=O (acyl halides) 1770-1815 sp C-H (alkynes) 3310-3320 C=O (esters) 1730-1750 sp

2 C-H (alkenes) 3000-3100 C=O (amides) 1680-1700

sp3 C-H (alkanes) 2850-2950

sp2 C-O (carbonyls) 1200 triple bond (alkynes) 2100-2200

sp3 C-O (alcoh., ethers) 1025-1200 triple bond (nitriles) 2240-2280

Bending Vibrations RCH=CH2 (alkenes) 910, 990 Monosubstituted benzene 730-770, 690-710 R2C=CH2 (alkenes) 890 ortho-disubstituted benzene 735-770 R2C=CHR’ (alkenes) 790-840 meta-disubstituted benzene 750-810, 680-730 para-disubstituted benzene 790-840

1



1. (8 pts) Provide the product(s) expected from each step of the following reaction sequence as well as detailed mechanisms for each step in the conversion of starting materials to product(s).

OO

1. xs LiAlH4, THF

2. H2O

[H AlH3]

HO

HH OH

O O

H O O

H

[H AlH3]

O

HH O

H OHH OH

2


1. m-CPBA, CH2Cl2

2. CH3MgBr, ether

3. H3O+ (quench)

1. NaBH4, CH3OH

1. PCC, CH2Cl2

a.

b.

c.

d.

e.

2. NaH, THF

3. CH3Br

2. H3O+ (quench)

3. (C4H9)4N+ F-

2. TsCl, pyridine3. KOtBu, THF

2. PhMgBr, THF

3. NH4Cl (aq)

1. xs CH3MgBr, ether

O

O

O

OH

O

O

O

OCH31. 2. 3.

CH3CH3

O

CH3

O

Ph

CH3

OH

Ph(+/-) (+/-) (+/-)

1. 2. 3.

OH 1. PDC, CH2Cl2 1. 2. 3.OO

CH3

(+/-)

OH

CH3

(+/-)

O

OMe

OSiMe3

1. 2. 3.O

CH3

OSiMe3

CH3

OH

CH3

OSiMe3

CH3

OH

CH3

OH

CH3

OH

OHMe 1. 2. 3.

O

OHMe

O

OTsMe

O

Me

(+/-) (+/-) (+/-)

3

3. (9 pts) Give the products expected to be formed from each step under the following conditions. Then draw complete mechanisms for each of the conversions.

1. NaSH, DMF

2. NaH, THF3. CH3CH2CH2Br

CH2Br

CH2S

CH2SCH2CH2CH3

H CH2S

Br

Na :H

4. (8 pts) From the molecules shown below, choose which one matches the following mass spectrum. Then

explain your choice, including reasons for why you didn’t pick the other possible answers. Atomic masses (in atomic mass units, a.m.u.) are as follows: C = 12 ; H = 1 ; F = 19 ; Cl = 35.45 ; Br = 79.90.

Each of the four possible answers would give the same base peak at m/z = 92 by losing the X atom/group from the methylbenzene ring, however only the bromo derivative would have M and M+2 signals due to the two naturally occurring isotopes of bromine. The approximately equal intensity of the two signals at 170 and 172 confirm this.

4

5. (14 pts) In the boxes below, provide the product(s) from each step of the following sequence. Using the spectroscopic and molecular formula clues might help you come up with answers.

6. (8 pts) Give the expected major product(s) expected to be formed under the following conditions as well as

a complete mechanism for its/their formation.

The benzene ring will not undergo substitution since SN1 and SN2 reactions do not occur at sp2 C.

5

7. (8 pts) Give the expected product(s) from each step of the following reaction sequence, and then provide a mechanism for each synthetic step.

8. (8 pts) Provide a retrosynthesis for the following ether that goes back to the sources of carbon shown. Then show how you would make the target molecule using any of the reactions seen so far in Chemistry 3719/ 3720. Include a product from each of your synthetic steps.

O

Retrosynthesis

O

Br HO

OH

OH

O

HOH

MgBrBr

Synthesis

HO

O

H

Br

PCC

CH2Cl2

MgBrMg

ether

OMgBr OH

ONaO

aq. NH4Cl

NaH, THF

HOPBr3

Br Br

6

9. (9 pts) Which of the following molecules does the IR spectrum below match? Explain your choice here by pointing out important signals that helped you to decide on your choice and why the spectrum does not match the other possibilities (Use the spectroscopy sheet for numbers).

The strong, broad signal at ~3300 cm-1 indicates an OH group, most likely in an alcohol. The carboxylic acid would have a C=O signal around ~1750, which is absent here; the ether would not have the strong

OH signal at ~3300 ; the ketone would show a strong C=O signal at ~1730, which is absent here. 10. (8 pts) For the following multi-step synthesis, give the product expected from each step as well as complete

mechanisms that describe all of the major events on the way from starting material to the final product.

1



HDI/Unsaturation Number = [#C atoms – ½#H atoms – ½#Halogen atoms + ½#N atoms] + 1 1. (9 pts) Provide the product(s) from each step of this reaction sequence as well as detailed mechanisms for

each step in the conversion of starting materials to product. Then draw the 1H NMR of the product.

2


1. Br2, heat

2. Na2Cr2O7, H2SO4

1. PhMe, reflux

1. HNO3, H2SO4

a.

b.

c.

d.

e.

2. Na2Cr2O7, H2SO4

2. NaCN, DMF

2. Sn, HCl

2. KOtBu

3. m-CPBA

1. HBr

1. Zn, HCl

O

H+

O

OH

O

3

3. (9 pts) Using Hűckel’s rule and Frost circles, indicate which of the following molecules will be aromatic and which will be anti-aromatic. Include the Hűckel calculation in each of your answers.

a.

b.

c.

4. (9 pts) Which one of the following compounds matches the spectral data given below? Your answer should

include reasoning for why you picked that compound and not the others.

O

O

O O

O

O

O

O

OH

OH

OH

a. b. c.

d. e. f.

O

1H NMR (CDCl3) ppm: 1.05 (s, 9H), 5.83 (d, 1H, J = 16 Hz), 6.71 (d, 1H, J = 16 Hz), 7.31-7.44 (m, 5H). 13C NMR (CDCl3) ppm: 29.5 (q, triple intensity), 32.9 (s), 114.5 (d), 121.6 (d, double intensity), 125.5 (d), 129.1 (d, double intensity), 151.3 (s), 158.2 (d), 164.3 (s).

4


, AlCl3

D2O

Final product:

Molecular formula = C13H19D

CH3COCl, AlCl3

MS: M+ = 184, M+2 = 186

13C NMR: 9 signals

Mg, ether

Zn, HCl

IR : 1740 cm-1

1H NMR: 0.98, 3H d

NaBH4, CH3OH

[ ]D = 0

C8H9MgBr

O

Cl

PBr3

6. (8 pts) Give the major and minor product expected to be formed under the following conditions as well as a

complete mechanism for their formation. Explain the major/minor distribution at this reaction temperature.

5

7. (14 pts) An unknown organic compound has the molecular formula C13H18O2; the mass spectrum shows M+ = 206 a.m.u., the IR spectrum shows significant signals at 1720, 1200, and 800 cm-1, and the 1H and 13C NMR spectra are given below. Suggest a structure for the unknown molecule that matches the data and then indicate which signals belong to which protons in the 1H NMR spectrum.

1H NMR (CDCl3) ppm : 0.98 (t, 3H, J = 7.1 Hz), 1.29 (d, 6H, J = 7.0 Hz), 1.51 (sextet, 2H, J = 7.1 Hz), 2.96 (t,

2H, J = 7.1 Hz), 4.69 (septet, 1H, J = 7.0 Hz), 7.01 (d, 2H, J = 7.5 Hz), 7.92 (d, 2H, J = 7.5 Hz).

13C NMR (CDCl3) ppm : 13.6 (q), 17.4 (t), 22.0 (q, double intensity), 40.4 (t), 75.8 (d), 114.3 (d, double

intensity), 129.4 (d, double intensity), 130.8 (s), 161.8 (s), 200.1 (s)

6

8. (9 pts) Provide a detailed mechanism for the following transformation that includes all important resonance structures for the intermediate involved. Then explain, briefly, the observed regioselectivity.

C N C N

Br

Br2, FeBr3

9. (8 pts) Which of the following diene compounds do you expect to participate in Diels-Alder reactions and

which will not? Explain your choices.

a.

b.

c.

d.







Approximate 13



-1)







1




1. (9 pts) Provide the product(s) expected from each step of the following reaction sequence as well as detailed mechanisms for each step in the conversion of starting materials to product.

2


1. Br2, heat

2. Na2Cr2O7, H2SO4

1. PhMe, reflux

1. HNO3, H2SO4

a.

b.

c.

d.

e.

2. Na2Cr2O7, H2SO4

2. NaCN, DMF

2. Sn, HCl

2. KOtBu

3. m-CPBA

1. HBr

1. Zn, HCl

O

H+

O

OH

O

O

H

O

H

1.

major (endo)

+

major (exo)

O

OH

O

OH

2.

+

1.

Br

(+/-)

2. 3.

(+/-)

O

1. 2.

H H

OH

O

1. 2.

Br CN

(+/-) (+/-)

1. 2.OH

O

OH

O

NO2 NH2

3

3. (9 pts) Using Hűckel’s rule and Frost circles, indicate which of the following molecules will be aromatic and which will be anti-aromatic. Include the Hűckel calculation in each of your answers.

a.

b.

c.

6 pi electrons, therefore 4n+2 =6; n =1integer + flat, fully conjugated = aromatic

6 pi electrons, therefore 4n+2 =6; n =1integer + flat, fully conjugated = aromatic

4 pi electrons, therefore 4n+2 =4; n =1/2non-bonding orbitals half full = antiaromatic

only bonding M.O.are populated

only bonding M.O.are populated

non-bonding M.O.half-populated

4. (9 pts) Which one of the following compounds matches the spectral data given below? Your answer should

include reasoning for why you picked that compound and not the others.

O

O

O O

O

O

O

O

OH

OH

OH

a. b. c.

d. e. f.

O

1H NMR (CDCl3) ppm: 1.05 (s, 9H), 5.83 (d, 1H, J = 16 Hz), 6.71 (d, 1H, J = 16 Hz), 7.31-7.44 (m, 5H). 13C NMR (CDCl3) ppm: 29.5 (q, triple intensity), 32.9 (s), 114.5 (d), 121.6 (d, double intensity), 125.5 (d), 129.1 (d, double intensity), 151.3 (s), 158.2 (d), 164.3 (s).

1.05

1.05

1.05

O

7.33

7.44

7.31

7.44

7.33

O

H

5.83

H6.71

29.5

32.9

158.2

114.5164.3

29.5

29.5

O151.3

121.6

129.1

125.5

129.1

121.6

O

13C signal at 164.3 indicates an ester so compounds a, c, and d don’t fit. Compound f would have three 1H signals for the alkene; the J value of 16 Hz indicates the trans alkene in compound e and not cis in b.

4


, AlCl3

D2O

Final product:

Molecular formula = C13H19D

CH3COCl, AlCl3

MS: M+ = 184, M+2 = 186

13C NMR: 9 signals

Mg, ether

Zn, HCl

IR : 1740 cm-1

1H NMR: 0.98, 3H d

NaBH4, CH3OH

[ ]D = 0

O OH

BrMgBrD

C8H9MgBr

O

Cl

D

O

D

H H

PBr3

6. (8 pts) Give the major and minor product expected to be formed under the following conditions as well as a

complete mechanism for their formation. Explain the major/minor distribution at this reaction temperature.

5

7. (14 pts) An unknown organic compound has the molecular formula C13H18O2; the mass spectrum shows M+ = 206 a.m.u., the IR spectrum shows significant signals at 1720, 1200, and 800 cm-1, and the 1H and 13C NMR spectra are given below. Suggest a structure for the unknown molecule that matches the data and then indicate which signals belong to which protons in the 1H NMR spectrum.

1H NMR (CDCl3) ppm : 0.98 (t, 3H, J = 7.1 Hz), 1.29 (d, 6H, J = 7.0 Hz), 1.51 (sextet, 2H, J = 7.1 Hz), 2.96 (t,

2H, J = 7.1 Hz), 4.69 (septet, 1H, J = 7.0 Hz), 7.01 (d, 2H, J = 7.5 Hz), 7.92 (d, 2H, J = 7.5 Hz).

13C NMR (CDCl3) ppm : 13.6 (q), 17.4 (t), 22.0 (q, double intensity), 40.4 (t), 75.8 (d), 114.3 (d, double

intensity), 129.4 (d, double intensity), 130.8 (s), 161.8 (s), 200.1 (s)

7.92

7.01 7.01

7.92

O2.96

1.51

0.98

O4.691.29

1.29

6

8. (9 pts) Provide a detailed mechanism for the following transformation that includes all important resonance structures for the intermediate involved. Then explain, briefly, the observed regioselectivity.

9. (8 pts) Which of the following diene compounds do you expect to participate in Diels-Alder reactions and

which will not? Explain your choices.

a.

b.

c.

Will react in Diels-Alder reactions since the diene is conjugated and trapped in the required s-cis conformation.

Will not participate in Diels-Alder reactions since the diene, eventhough conjugated, is trapped in the s-trans orientation.

Will not participate in Diels-Alder reactions since the diene is notconjugated; the alkenes are isolated.

d. Will participate in Diels-Alder reactions since the diene is bothconjugated and can rotate to the required s-cis conformation.

1



HDI/Unsaturation Number = [#C atoms – ½#H atoms – ½#Halogen atoms + ½#N atoms] + 1 1. (8 pts) Provide a complete mechanism for the following conversion that includes resonance structures for

any intermediates that are formed. What experimental measures would you take to push this reaction completely to product?

2

2. (9 pts) Starting with benzene, provide a synthesis of methyl 3-aminobenzoate using any of the chemistry and reagents seen thus far in 3719 and 3720. Show the major product from each step; however you do not need to show a retrosynthesis unless it helps you to develop the synthetic route.

3. (10 pts) Draw a complete mechanism for the following sequence that includes all resonance structures for

any intermediates that are formed along the reaction profile.

3


1. PCC, CH2Cl2

2. NaBH4, CH3OH

3. Sn, HCl

1. SOCl2

1. H3O+ (hydrolysis)

a.

b.

c.

d.

e.

2. HN(CH2CH3)2

3. LiAlH4, then H2O

2. xs. CH3OH, cat. H+

3. Br2, FeBr3

2. PhMgBr, ether

3. H+ quench

2. NH2NH2, cat. H+

3. KOH, H2O, reflux

1. Na2Cr2O7, H2SO4

1. HNO3, H2SO4

O

OMe

OH

O

OH

OMe

4


SOCl2

Final product:

Molecular formula = C8H8O

NaBH4, CH3OH

IR : 2250 cm-1

13C NMR: 7 signals

H+/H2O/

H-Al(i-Bu)2

IR : 3200 cm-1

acid chloride

C7H7Br

IR : 3200, 1740 cm-1

NaCN, DMF

H

OPBr3

24 hours

then H+ workup

CH3OH, pyridine

6. (7 pts) Provide a complete mechanism for the following transformation that includes all resonance structures

for the intermediate that is formed.

5

7. (8 pts) Give a complete mechanism for the following nitrile hydrolysis that includes all important resonance structures for any intermediates that are formed.

8. (8 pts) By using curved arrows, show how the following aldol transformation occurs. Draw all important

resonance structures where applicable.

6

9. (8 pts) Draw a complete mechanism for the following alpha-bromination reaction that includes all resonance structures for any intermediates that formed along the way from starting material to product.

10. (8 pts) Give the structure of the major product expected from each step in the following synthetic sequence. No need to show mechanisms here.

OH

1. PCC, CH2Cl2

2. Br2, FeBr3

3. xs CH3OH, cat. H+

4. Mg, ether

5. D2O

6. H+/H2O (hydrolyze)

7. PPh3

1



HDI/Unsaturation Number = [#C atoms – ½#H atoms – ½#Halogen atoms + ½#N atoms] + 1 1. (8 pts) Provide a complete mechanism for the following conversion that includes resonance structures for

any intermediates that are formed. What experimental measures would you take to push this reaction completely to product?

cat. H+

OO O

HOCH2CH2OHH+

OH

OH

HOCH2CH2OH

O

OH

OHH O

OH

OH2H+ trans

O

OH

O O H

ROH

- H2O

Use a drying agent like anhydrous MgSO4 to remove the water and push the equilibrium to product.

2

2. (9 pts) Starting with benzene, provide a synthesis of methyl 3-aminobenzoate using any of the chemistry and reagents seen thus far in 3719 and 3720. Show the major product from each step; however you do not need to show a retrosynthesis unless it helps you to develop the synthetic route.

3. (10 pts) Draw a complete mechanism for the following sequence that includes all resonance structures for

any intermediates that are formed along the reaction profile.

O N HNH2

H

NH2NH2

cat. H+

KOH, H2O

heat

OH

OH

HO N NH2

H

HH2O N NH2

H

NNH2H

NNH2H

NN

H

H NN

H

NN

H

NN

H

H NN

H H HH

H+

NH2NH2 H+ trans

- H2O - H+OH

HO H

OH - N2 OHH

3


1. PCC, CH2Cl2

2. NaBH4, CH3OH

3. Sn, HCl

1. SOCl2

1. H3O+ (hydrolysis)

a.

b.

c.

d.

e.

2. HN(CH2CH3)2

3. LiAlH4, then H2O

2. xs. CH3OH, cat. H+

3. Br2, FeBr3

2. PhMgBr, ether

3. H+ quench

2. NH2NH2, cat. H+

3. KOH, H2O, reflux

1. Na2Cr2O7, H2SO4

1. HNO3, H2SO4

O

OMe

OH

O

OH

Cl

O

NEt2

O

NEt2

H H1. 2. 3.

O NNH2 H H1. 2. 3.

O OH OH1. 2. 3.

NO2 NO2 NH2

OH

O

OCH3

O

OCH3

O1. 2. 3.

Br

H

O

H

O

H

HO1. 2. 3.

Ph PhOMe

4


6. (7 pts) Provide a complete mechanism for the following transformation that includes all resonance structures

for the intermediate that is formed.

5

7. (8 pts) Give a complete mechanism for the following nitrile hydrolysis that includes all important resonance structures for any intermediates that are formed.

CN H+/H2O/

24 hours

O

OH

CN

H

CN

H

C

NH

OH2

C

NH2

OH

C

NH2

OH

C

NH2

OH

C

NH2

OHOH2

C

NH3

OHOH

COH

OH

COH

OH

COH

OH

H+

H2O

OH2

H+ trans

- H+

8. (8 pts) By using curved arrows, show how the following aldol transformation occurs. Draw all important

resonance structures where applicable.

H

O

H

ONaOCH3, CH3OH

reflux

H

H

H

O

H

O

H

O

H

H

OH O

H

OH OH

H

H

OH OH

H

OH OH

CH3O

H OCH3

OCH3

OH_

6

9. (8 pts) Draw a complete mechanism for the following alpha-bromination reaction that includes all resonance structures for any intermediates that formed along the way from starting material to product.

O

Br2/H3O+

O

BrH+

OH

OH

H

OH

OH

Br

OH

BrOH2

Br Br

- H+

10. (8 pts) Give the structure of the major product expected from each step in the following synthetic sequence. No need to show mechanisms here.

1


This exam is worth 200 points out of a total of 700 points for Chemistry 3720/3720L. You have 120 minutes to complete the exam. The spectroscopy sheet is attached as the last page. Good Luck!

HDI/Unsaturation Number = [#C atoms – ½#H atoms – ½#Halogen atoms + ½#N atoms] + 1 1. (8 pts) For the following Wittig reaction sequence, give the products expected from each step and then a

complete mechanism for the conversion of the alkyl halide into the final product.

2

2. (8 pts) A new medicinal compound, isolated from a tropical plant, has one of the following structures. Using the provided spectral data, indicate which structure is correct and then explain your decision by matching the data to the structure.

Selected data: IR : 3350, 3000, 1690 cm-1 ; 13C NMR : 170, 150, 120 ppm ; 1H NMR : 6.0 ppm (s, 1H)

3. (8 pts) In the following reaction one major product is formed with molecular formula C7H5N3O6. The

molecule has 5 signals in its 13C NMR spectrum and 2 signals in the 1H NMR. Draw the product; give a mechanism for the first nitration, and finally a brief explanation for the observed regioselectivity.

3

4. (8 pts) Provide a detailed mechanism for the following prostaglandin synthesis that includes all important resonance structures for intermediates that are formed. Use “R” groups for brevity where possible.

5. (8 pts) Draw a detailed mechanism for the following ester conversion that includes all important resonance structures for any intermediates that are formed.

4

6. (20 pts) Provide the expected major products from each step of the following reaction sequences. Be sure to take tautomerism into consideration where applicable.

1. PCC, CH2Cl2

2. H+ quench

3. NaBH4, CH3OH

1. Br2, H3O+

1. PhMgBr, ether

a.

b.

c.

d.

e.

2. KOt-Bu

3. NaBH4, CH3OH

2. NH2NH2, cat. H+

3. KOH, D2O,

2. H+ quench

3. m-CPBA, CH2Cl2

2. LDA, THF

3. CH3CH2CH2Br

1. H2, Pd

1. (CH3)2CuLi, THF

O

OH

O

O

O

5


H+ quench

Final product:

Molecular formula = C9H20O3Si

Na2Cr2O7, H2SO4

IR : 1740 cm-1

IR 3300, 1740 cm-1

NaOEt, EtOH

(CH3)3SiCl

IR : 2700, 1740 cm-1

IR 1750, 1710 cm-1

C2H3ClO

EtOH, pyridine

SOCl2

NaBH4, EtOH

OH

Et3N

C6H9NaO3

6. (8 pts) Provide a complete mechanism for the following transformation that explains how the two regio-

isomeric products are formed.

6

7. (9 pts) Starting with benzene, provide an efficient synthesis of 4-nitrobenzoic acid that employs any of the chemistry seen throughout Chemistry 3719 and 3720. Provide the product from each step.

8. (10 pts) Give a retrosynthesis for this molecule that goes back to cyclohexanol and ethanol as the only

sources of carbon. Then build the molecule in the forward direction showing the product from each step.

O

7

9. (8 pts) Draw Frost circles and apply Hückel’s rule to decide if each of the following molecules is aromatic or not. You need to show the results of your Hückel calculations for full credit.

10. (8 pts) Draw the structure of the monomer precursor that would be needed to produce each of the four

polymers below. Label each polymer as being either the “addition” or “condensation” type.

a.

b.

c.

N

H

O

CH3

N

H

O

CH3

N

H

O

O

O

OO

O

O

O

d.

8

11. (8 pts) Draw a complete mechanism for the following cyclization process that includes all resonance structures for any intermediates that formed along the way from starting material to product. Use “R” groups to abbreviate structures as appropriate.

12. (8 pts) Give the structure of the major product expected from each step in the following synthetic sequence as well as detailed mechanisms for their formation.

N

O

O

H

1. KOH, EtOH

Br2.

3. NH2NH2

9

13. (14 pts) An unknown organic compound has the molecular formula C11H14O2; the mass spectrum shows M+ = 178.10 a.m.u., the IR spectrum shows significant signals at 1740, 1050, 760 and 690 cm-1, and the 1H and 13C NMR spectra are given below. Suggest a structure for the unknown molecule that matches the data and then indicate which signals belong to which protons in the 1H NMR spectrum.

1H NMR (CDCl3) ppm : 1.20 (d, 6H, J = 7.1 Hz), 2.87 (septet, 1H, J = 7.1 Hz), 3.89 (singlet, 3H), 7.35 (t, 1H, J

= 7.5 Hz), 7.49 (d, 1H, J = 7.5 Hz), 7.89 (d, 1H, J = 7.5 Hz), 7.99 (s, 1H).

13C NMR (CDCl3) ppm : 23.3 (q, double intensity), 33.2 (d), 51.5 (q), 127.1 (d), 127.2 (d), 128.3 (d), 129.8 (s), 130.4 (d), 150.0 (s), 165.9 (s)

10

14. (7 pts) Provide a complete mechanism for the following Baeyer-Villiger oxidation. Then try to explain the regioselectivity observed in this reaction.

15. (7 pts) Give a detailed mechanism for the following reductive amination reaction that includes resonance structures for any intermediates that are formed.

16. (7 pts) Draw a detailed mechanism for the following cyclization reaction that includes resonance structures for any intermediates that are formed.

11

17. (8 pts) Provide a complete mechanism for the following “iodoform” reaction that includes all resonance structures for any intermediates that are formed.

18. (8 pts) Give the expected products for the two epoxide reactions shown below as well as mechanisms for their formation that include any important resonance structures. How do your mechanisms explain the observed optical rotation data?

12

19. (8 pts) For the following Robinson annulation, provide a detailed step-by-step mechanism that explains the formation of the third cycle. Include resonance structures where relevant.

20. (8 pts) The following molecule is a pentasaccharide that induces antibodies to epithelial cancer cells when conjugated to various proteins. When this molecule is treated with H+/H2O it is hydrolyzed to the five individual monosaccharides by cleavage of each of the acetal linkages. Circle each acetal carbon in the pentasaccharide and then draw the five reducing sugars expected to be formed after acetal hydrolysis.







Approximate 13



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Chemistry 3720 Old Exams - hyperconjugation.com · Organic Chemistry Spectral Data Sheet Approximate 1H NMR Chemical Shifts (parts per million) R 3 C-H (alkyl) 0.9 to 1.8 R 3 N-C-H