Exam 3 - 2019 - Key - Exam 3 answer key PDF

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Name: _____________________________________

ORGANIC CHEMISTRY II CHEM2220 Wednesday, November 20, 2019 KEY Instructions: Print your name in the spaces provided on every sheet of the exam. Failure to do so will lead to loss of credit. Make sure that you do the problems on the front and back of every sheet. On multiple choice questions, clearly circle the answer that you think is correct. Exams that are done in pencil, red ink, erasable ink, or that have white-out on them will not be considered for regrades. Question #

Possible Points

Points Scored

1

30

__________

2

8

__________

3

8

__________

4

32

__________

5

12

__________

6

10

__________

__________ 100 TOTAL

1

1. Multiple Choice Questions. Clearly circle your chosen answer.

(30 points; 3 each)

a) The reagent best used to convert C6H5CH2C(O)OH to C6H5CH2C(O)Cl would be HCl

HOCl

SOCl2

Cl2

b) For the following transformation, the most likely product would be

NH2

1) NaNO2, HCl 2) CuCN 3) H3O+, heat

Cl

OH

NO2

CO2H

CH3

CH3

CH3

CH3

? CH3

c) One method for synthesis of a carboxylic acid involves conversion of a bromide to the corresponding cyano compound, followed by hydrolysis. This reaction sequence would work with any of the following halides, except _____.

Br

Br

CH3

OH

Br

Br

Br

d) Of the following reaction conditions, which one will drive the equilibrium of a Fischer esterification towards ester formation? addition of catalytic base

addition of water

removal of water as it is formed

removal of the amine as it is formed 2

Name: ________________________________________ e) A Dean-Stark trap is used to _______. a) heat a reaction at the boiling point of a solvent.

b) remove water from an equilibrium reaction by azeotrope formation. -

c) separate two non volatile compounds.

d) separate two volatile compounds based on their boiling points.

f) Of the following compounds, the one that should undergo nucleophilic attack at the carbonyl group the most rapidly would be ------. (circle one). O

O

O

O

O

O NH

NH

O

g) The reaction shown below would be expected to yield which product? O NH

Br

+

1) base 2) H2NNH2, heat ?

Br O

Br H2N

NH2 Br

NH2

NHNH2 Br

3

H2N

h) Carboxylic acids can be reduced to aldehydes by:

1) conversion to the ester followed by treatment with LiAlH 4

2) conversion to the amide followed by treatment with NaBH4

3) treatment with a limited amount of LiAlH4

4) conversion to the acid chloride followed by treatment with LiAlH[OC(CH3) 3]3.

i) Which of the reagents listed below would accomplish the following transformation? O O

?

Cl

H2C=CHLi

(H2C=CH)2CuLi

H2C=CHMgBr

Any of these three reagents would work.

j) As shown below, this reaction would yield___. O

O

a) H3 C O

O OH

b)

OH

O O

O

OH H3 CCOCCH3

O

O

OH

OH and

4

O 2 HOCCH3

d)

O HOCCH3

CH3 O

H

c)

OH and

O O

OH and

CH3 O HOCCH3

Name: ________________________________________ 2. Comparison Questions. Clearly circle your chosen answer.

(8 points; 2 each)

a) When methyl benzoate is subjected to acid catalyzed hydrolysis in H218O, which product will contain the 18O isotope?

Methanol

Benzoic Acid

b) The starting material which would give the desired product under the conditions shown below should be -------- (circle one). O

1) DIBAL + 2) H3 O

H

?

CN

OH

or

c) Protonation of ethyl acetate would be expected to favor which structure?

: O: C .. OCH2CH3 H or H :O C .. OCH2CH3 H3C .. H3C

+ H

O H3C

C

OCH2CH3

d) Which compound is the stronger acid? H3CCO2H

or

5

F3CCO2H

3. Provide short answers for each of the following questions: (4 each) a) When aniline was treated under the conditions shown below, a single product was obtained which gave deceptively simple spectral data. The 13C NMR of the product is shown below. On the basis of this data, propose a structure for this product. (Note, no resonances were observed below 100 ppm in the carbon spectrum).

NH2

NaNO2, HCl 0 °C, H2O

C 6H5OH NaOH 0 °C, H2O

OH

?

6

N

N

Name: ________________________________________ b) A student in organic lab, who may (or may not) have been prepared for the experiment, treated the aldehyde 3b in the sequence of reactions shown below. When the product was isolated, it gave the following NMR spectra. Propose a structure for this product that would be consistent with these spectra. O 1) LiAlH4 H 3b OH

H2NOH H+

2) H3O+

? 3c

1

NH2 OH 3 2 _ __ 2 1

7

4. Synthesis and mechanisms.

(32 points; 8 each)

a) A sequence of several steps is required to convert compound 4a to the desired product 4b. List the reagents required for each step in this sequence. You can use any necessary inorganic reagents and any organic reagents containing two carbons or less.

???

CH2CO2H

CH2CH2NHCH2CH3

4a

4b 1) SOCl2 2) H2 NCH2 CH3 3) LiAlH4 4) H2 O (or H+/H2 O)

b) The reaction shown below generates an intermediate which cannot be isolated because it is rapidly consumed by further reaction. a. Propose a reasonable mechanism for formation of the intermediate A from the initial reagents, and b. Briefly explain why this intermediate cannot be isolated from this reaction.

O MgBr H

O CH2CH3

+

2

A

O O H H

O CH2 CH3 A

MgBr The aldehyde A is a more reactive electrophile than the original ester.

8

H3O+

B

Name: ________________________________________ c) When the amine 4c is allowed to react with methyl iodide followed by treatment with silver oxide, a crystalline compound is obtained (4d). This product is sufficiently stable to be isolated, but when it is heated it undergoes further reaction to give one major final product (4e). Considering this information, a. Provide a reasonable structure for the intermediate compound 4d, and b. Provide a detailed mechanism that explains the formation of the product 4e from intermediate 4d.

H3CCHCH2CH3 NH2

1) excess ICH3 2) Ag2O, H2O

heat 4d

4e

4c H2C CHCH2CH3 OH H H2C __CHCH2CH3 N(CH3)3

d) Describe below an efficient synthesis of the carboxylic acid ester 4g from the alkane 4f. Multiple steps may be required. ? H3CCH2CH2CH2CH2CO2CH2CH3 H3CCH2CH2CH2CH2Br

4f

4g H3 CCH2 OH

Na + CN-

H+ H3O+

H3 CCH2 CH2 CH2 CH2 CN

H3CCH2CH2 CH2 CH2 CO2 H

9

5. Provide the missing product(s) or reactants for the following reactions. More than one step may be necessary. If more than one product is formed, indicate which is the major and which is the minor product. If any reaction gives a mixture of ortho and para products, you can assume that they are separable. If there is no reaction, clearly indicate that. (12 points; 4 each) a)

CH3

1) ? 2) ?

?

?

CH3 HO2C

Br2,FeBr3

Mg, ether 1) CO2 2) H3O+ (or Gatterman-Koch strategy to aldehyde and oxidation of resulting aldehyde)

b)

H2N O

?NH2

O

H

1) LiAlH4 + 2) H3O

? H

Cl

O

N

H N

N H

N

c)

Br

NH2

?

?

?

OH

N3

OH 1) LiAlH4

NaN3

2) H3O+

10 OH (or Gabriel synthesis)

Name: ________________________________________ 6. (10 pts) A synthetic chemical that is commonly found in cosmetics and soaps was determined to have the formula C9H10O3, and gave the NMR spectra shown below. (The 13C resonances are found at 167.6, 160.8, 132.0, 122.2, 115.4, 61.2, and14.3 ppm.) Propose a structure for this compound that would be consistent with this data. solvent

3 2 2 2 1

O OCH2CH3 HO

11

Type of Hydrogen

δ(ppm)

sp3 C-H RCH3 R2CH2 R3CH

0.9 – 2 ~0.9 ~1.3 ~1.7

Z

Z = C, O, N

C

C

H

1.5 – 2.5

-C≡C-H

~2.5 H

Z = N, O, X

2.5 – 4

C Z

H C

R

4.5 – 6

C

O

O

C

C

H

R

H

6.5 – 8

OH

9 – 10 10 – 12

RO-H or R2N-H

1–5 12

Type of Carbon

δ (ppm)

sp3 C-H

5 – 45

―C≡C―

65 – 100

H Z = N, O, X

C

30 - 80

Z C

C

100 – 140

C

120 – 150

C O

160 – 210

13...