chemistry 2220 final exam - university of manitobahultin/chem2220/archive/2017/2017... · page 1 of...

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CHEM 2220 Organic Chemistry II: Reactivity and Synthesis Prof. P.G. Hultin

FINAL EXAM – Winter Session 2017R

Tuesday April 25, 2017 8:00 am – 11:00 am Frank Kennedy Gold Gym

PRINT LEGIBLY PLEASE

Name: Student Number: Email:

This is a closed-book time-limited invigilated exam. Students are permitted to bring into the exam room

ONE SHEET of LETTER-SIZE (8½ x 11 inches) paper with any HANDWRITTEN notes they wish (both sides).

Molecular model kits, rulers and calculators are permitted but no other aids may be used.

The exam is divided into 5 parts, with total marks as noted below. All answers are to be written in the spaces

provided in this stapled package. Submit this package when you are finished writing the exam. Please do not put

your name or student number on individual pages of this package. Only put identification on this title page.

The separate spectroscopy page will not be handed in and you should not write answers there.

Part 1 – Reactions and Products (40 Marks)

Part 2 – Synthesis (15 Marks)

Part 3 – Mechanism (14 Marks)

Part 4 – Mechanism pot-pourri (24 Marks)

Part 5 – Spectroscopy (7 Marks)

TOTAL: (100 Marks)

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1. (40 MARKS) Reactions and Products. Supply the missing molecular structure or reagent/solvent/reaction

conditions to correctly complete the following reactions. Show stereochemistry when necessary. If a

compound is racemic, indicate this by writing “racemic” or “+/-“. Simple aqueous acid or base workups can be

assumed but any “special” workup conditions should be specified.

(a) (2 Marks)

(b) (2 Marks)

(c) (2 Marks)

(d) (2 Marks)

(e) (2 Marks)

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(f) (4 Marks)

(g) (2 Marks)

(h) (2 Marks)

(i) (2 Marks)

(j) (2 Marks)

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(k) (4 Marks)

(l) (4 Marks)

(m) (4 Marks)

(n) (2 Marks)

(o) (4 Marks)

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2. (15 MARKS) Propose a practical synthetic route to prepare 2-chromanone starting from phenol. You

may use any other reagent or solvent needed. There are at least 2 routes based on reactions covered in

CHEM 2220 that require fewer than SIX steps.

(a) (5 Marks) Give a stepwise retrosynthetic analysis describing your route. Remember to use the

correct retrosynthetic arrows for each disconnection step in your analysis.

(b) (10 Marks) Re-write your route in the forward synthetic direction. For each step, provide the specific

reagents and conditions and the structure of the product formed.

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3. (14 MARKS TOTAL) The following reaction was a key step in a synthesis of a cytotoxic alkaloid called

Crispine A published in 2011. The researchers noted that the intermediate X was formed very rapidly at room

temperature, and it could be observed by NMR in the reaction mixture. The spectra clearly showed that

compound X contained an RCH2Cl group. Intermediate X was converted more slowly into the final product.

(a) (2 Marks) Identify the most nucleophilic atom in the reactants.

(b) (2 Marks) An acetal can be hydrolyzed by aqueous acid. There is no water in this reaction, but

there is an acid present! Use these facts to write an arrow-pushing mechanism showing

how an electrophilic site is created from the acetal reactant.

(c) (2 Marks) Number the carbon atoms in the acetal reactant and then apply the same numbers to the

corresponding atoms in the product structure. (The atoms from the amino-ester should

be obvious).

Part d of this question is on the next page of this exam!

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(d) (8 Marks) Use the information you now have to write a mechanism for the overall reaction, and

identify intermediate X in your mechanism.

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4. (24 MARKS TOTAL) Mechanism pot-pourri! Assorted shorter mechanisms from across the course.

(a) (8 Marks) The beauty of pericyclic reactions is their ability to achieve enormous structural changes

with exquisite stereochemical control. Provide mechanisms for the two transformations of

compound A shown below. Identify the type of reaction, how many pi electrons are

involved and whether the processes are conrotatory or disrotatory.

(b) (6 Marks) When the α,β-unsaturated ketone shown was boiled in the presence of polyphosphoric

acid, 3-phenyl-1-indanone was obtained in moderate yield. Provide a stepwise

mechanism for this transformation. You can represent polyphosphoric acid by “H+”.

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(c) (4 Marks) Di-iodination of alkenes and alkynes is not usually a thermodynamically favourable

reaction, but this interesting process was extremely efficient, giving the product in 94%

isolated yield. Taking into account the fact that sp2 cations are very high-energy

intermediates, write a plausible mechanism to explain this process.

(d) (6 Marks) Provide a plausible reaction mechanism for the following reaction. Notice the

stereochemical relationships between the starting material and the product.

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5. (7 MARKS Total) Spectroscopy. The molecular formula of an unknown organic compound is C9H7NO3.

The IR, 13C NMR and 1H NMR spectra of this compound are attached to the exam. Answer the following

questions about this compound based on these spectra.

(a) (1 Mark) What is the unsaturation number for this compound?

(b) (1 Mark) What functional group contains the nitrogen atom, and what spectroscopic evidence

supports your conclusion?

(c) (2 Marks) What specific functional group gives rise to the 13C NMR signal at 192 ppm? What other

spectroscopic evidence supports your conclusion?

(d) (1 Mark) There are two doublets each integrating for 2H in the 1H NMR spectrum at 8.31 and 7.76

ppm. What structural conclusion can be drawn from these?

(e) (1 Mark) What do the two 1H signals at 7.57 and 6.83 ppm tell us about the structure? Explain their

J-coupling.

(f) (1 Mark) Draw the structure of this compound in the box below.

Structure for C9H7NO3

CHEM 2220 Final 2017R THIS PAGE NOT TO BE HANDED IN Page 1 of 2

Spectra for Part 5

IR

C9H7NO3

13C NMR C9H7NO3

NB: solvent peaks have been edited out.

1H NMR

C9H7NO3

1H

d

2H

d

2H

d

1H

dd 1H

d

J = 16.2 Hz J = 16.2 Hz

and 7.5 Hz

J = 7.5 Hz

THIS PAGE NOT TO BE HANDED IN Page 2 of 2

Spectroscopy “Crib Sheet” for CHEM 2220 – Introductory Organic Chemistry II

1H NMR – Typical Chemical Shift Ranges

Type of Proton Chemical Shift (δ) Type of Proton Chemical Shift (δ)

C CH3 0.7 – 1.3 C C H 2.5 – 3.1

C CH2 C 1.2 – 1.4

O

H

9.5 – 10.0

C H

C

C

C

1.4 – 1.7

O

OH

10.0 – 12.0

(solvent dependent)

C H

1.5 – 2.5 C OH

1.0 – 6.0

(solvent dependent)

O

H

2.1 – 2.6 CO H

3.3 – 4.0

Aryl C H 2.2 – 2.7 CCl H

3.0 – 4.0

H

4.5 – 6.5 CBr H

2.5 – 4.0

Aryl H 6.0 – 9.0 CI H

2.0 – 4.0

13C NMR – Typical Chemical Shift Ranges

IR – Typical Functional Group Absorption Bands

Group Frequency

(cm-1) Intensity Group

Frequency (cm-1)

Intensity

C–H 2960 – 2850 Medium RO–H 3650 – 3400 Strong, broad

C=C–H 3100 – 3020 Medium C–O 1150 – 1050 Strong

C=C 1680 – 1620 Medium C=O 1780 – 1640 Strong

C≡C–H 3350 – 3300 Strong R2N–H 3500 – 3300 Medium, broad

R–C≡C–R′ 2260 – 2100 Medium (R ≠ R′) C–N 1230, 1030 Medium

Aryl–H 3030 – 3000 Medium C≡N 2260 – 2210 Medium

Aryl C=C 1600, 1500 Strong RNO2 1540 Strong

12 11 10 9 8 7 6 5 4 3 2 1 0

R3C–H

Aliphatic, alicyclic X–C–H

X = O, N, S, halide

Y

H H

Aromatic,

heteroaromatic

Y

H

RCO2H

Y = O, NR, S Y = O, NR, S

“Low Field” “High Field”

220 200 180 160 140 120 100 80 60 40 20 0

CH3-CR3

CHx-C=O

CR3-CH2-CR3

CHx-Y: Y = O, N Alkene

Aryl

Amide

Ester Ketone,

Aldehyde

Acid RCN RCCR

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CHEM 2220 Organic Chemistry II: Reactivity and Synthesis Prof. P.G. Hultin

FINAL EXAM – Winter Session 2017R

Tuesday April 25, 2017 8:00 am – 11:00 am Frank Kennedy Gold Gym

PRINT LEGIBLY PLEASE

Name: ANSWER KEY Student Number: Email:

This is a closed-book time-limited invigilated exam. Students are permitted to bring into the exam room

ONE SHEET of LETTER-SIZE (8½ x 11 inches) paper with any HANDWRITTEN notes they wish (both sides).

Molecular model kits, rulers and calculators are permitted but no other aids may be used.

The exam is divided into 5 parts, with total marks as noted below. All answers are to be written in the spaces

provided in this stapled package. Submit this package when you are finished writing the exam. Please do not put

your name or student number on individual pages of this package. Only put identification on this title page.

The separate spectroscopy page will not be handed in and you should not write answers there.

Part 1 – Reactions and Products (40 Marks)

Part 2 – Synthesis (15 Marks)

Part 3 – Mechanism (14 Marks)

Part 4 – Mechanism pot-pourri (24 Marks)

Part 5 – Spectroscopy (7 Marks)

TOTAL: (100 Marks)

of 10

1. (40 MARKS) Reactions and Products. Supply the missing molecular structure or reagent/solvent/reaction

conditions to correctly complete the following reactions. Show stereochemistry when necessary. If a

compound is racemic, indicate this by writing “racemic” or “+/-“. Simple aqueous acid or base workups can be

assumed but any “special” workup conditions should be specified.

(a) (2 Marks)

(b) (2 Marks)

(c) (2 Marks)

(d) (2 Marks)

(e) (2 Marks)

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(f) (4 Marks)

(g) (2 Marks)

(h) (2 Marks)

(i) (2 Marks)

(j) (2 Marks)

of 10

(k) (4 Marks)

(l) (4 Marks)

(m) (4 Marks)

(n) (2 Marks)

(o) (4 Marks)

of 10

2. (15 MARKS) Propose a practical synthetic route to prepare 2-chromanone starting from phenol. You

may use any other reagent or solvent needed. There are at least 2 routes based on reactions covered in

CHEM 2220 that require fewer than SIX steps.

(a) (5 Marks) Give a stepwise retrosynthetic analysis describing your route. Remember to use the

correct retrosynthetic arrows for each disconnection step in your analysis.

(b) (10 Marks) Re-write your route in the forward synthetic direction. For each step, provide the specific

reagents and conditions and the structure of the product formed.

Several variations in reagents are possible, and we can’t really tabulate every single one. Any

chemistry that works gets marks.

Likewise, there are probably other retrosynthetic analyses that can be devised, which would lead

to different syntheses. If the chemistry is ok, there is no problem.

of 10

3. (14 MARKS TOTAL) The following reaction was a key step in a synthesis of a cytotoxic alkaloid called

Crispine A published in 2011. The researchers noted that the intermediate X was formed very rapidly at room

temperature, and it could be observed by NMR in the reaction mixture. The spectra clearly showed that

compound X contained an RCH2Cl group. Intermediate X was converted more slowly into the final product.

(a) (2 Marks) Identify the most nucleophilic atom in the reactants.

(b) (2 Marks) An acetal can be hydrolyzed by aqueous acid. There is no water in this reaction, but

there is an acid present! Use these facts to write an arrow-pushing mechanism showing

how an electrophilic site is created from the acetal reactant.

(c) (2 Marks) Number the carbon atoms in the acetal reactant and then apply the same numbers to the

corresponding atoms in the product structure. (The atoms from the amino-ester should

be obvious).

Part d of this question is on the next page of this exam!

The amine nitrogen in the amino acid is the most nucleophilic.

of 10

(d) (8 Marks) Use the information you now have to write a mechanism for the overall reaction, and

identify intermediate X in your mechanism.

of 10

4. (24 MARKS TOTAL) Mechanism pot-pourri! Assorted shorter mechanisms from across the course.

(a) (8 Marks) The beauty of pericyclic reactions is their ability to achieve enormous structural changes

with exquisite stereochemical control. Provide mechanisms for the two transformations of

compound A shown below. Identify the type of reaction, how many pi electrons are

involved and whether the processes are conrotatory or disrotatory.

(b) (6 Marks) When the α,β-unsaturated ketone shown was boiled in the presence of polyphosphoric

acid, 3-phenyl-1-indanone was obtained in moderate yield. Provide a stepwise

mechanism for this transformation. You can represent polyphosphoric acid by “H+”.

Protonating the C=C bond directly will

also form a carbocation at the required

location, but 1) the oxygen is more basic,

and 2) the cation is more delocalized

hence likely lower in energy.

of 10

(c) (4 Marks) Di-iodination of alkenes and alkynes is not usually a thermodynamically favourable

reaction, but this interesting process was extremely efficient, giving the product in 94%

isolated yield. Taking into account the fact that sp2 cations are very high-energy

intermediates, write a plausible mechanism to explain this process.

(d) (6 Marks) Provide a plausible reaction mechanism for the following reaction. Notice the

stereochemical relationships between the starting material and the product.

of 10

5. (7 MARKS Total) Spectroscopy. The molecular formula of an unknown organic compound is C9H7NO3.

The IR, 13C NMR and 1H NMR spectra of this compound are attached to the exam. Answer the following

questions about this compound based on these spectra.

(a) (1 Mark) What is the unsaturation number for this compound?

(b) (1 Mark) What functional group contains the nitrogen atom, and what spectroscopic evidence

supports your conclusion?

(c) (2 Marks) What specific functional group gives rise to the 13C NMR signal at 192 ppm? What other

spectroscopic evidence supports your conclusion?

(d) (1 Mark) There are two doublets each integrating for 2H in the 1H NMR spectrum at 8.31 and 7.76

ppm. What structural conclusion can be drawn from these?

(e) (1 Mark) What do the two 1H signals at 7.57 and 6.83 ppm tell us about the structure? Explain their

J-coupling.

(f) (1 Mark) Draw the structure of this compound in the box below.

Structure for C9H7NO3

Unsaturation = 7

Probably NO2 – IR band at ~1550, no evidence of N-H in IR or 1H NMR.

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