FACULTY OF SCIENCE

TERM TEST #2

A N S W E R S

COURSE NAME Organic Chemistry

COURSE NUMBER CHEM 2120U

INSTRUCTOR J.W. Easton

DATE 2011-03-15

TIME 1.0 hour

INSTRUCTIONS TO STUDENTS

1. A complete test includes answers to: PART A………………………… 10 multiple-choice questions ………………..… 10 marks PART B………………………... 3 questions ……………….........………...........… 10

marks PART C................................ 3 questions ..................................................

10 marks

2. Multiple choice questions have one and only one answer. Answer each of the questions by circling the letter (A,B,C,D,E) on the question booklet that represents the correct answer.

3. Please keep the Booklet intact. Do not remove any pages from the Booklet. At the conclusion

of the test, the complete Term Test Booklet and the Seating Arrangement Form should be submitted.

4. Unless noted otherwise, all chemical structures should be in the condensed form (CH3-, -CH2-, etc) and should not be in skeletal form.

5. This is a closed book exam. Rough work can be done on the blank pages at the end of the test.

6. Calculators are not permitted nor required.

PART A - Multiple-choice Questions (10 x 1 = 10 marks)

Answer the following questions by circling the letter (A,B,C,D,E) on the question booklet that represents the correct answer.

1. Given the following compounds, arrange them in order of increasing acid strength (the weakest acid is identified first and the strongest acid is identified last):

I II III IV V

A. III, IV, V, II, IB. IV, III, V, I, IIC. I, II, III, IV, VD. V, II, I, III, IVE. II, I, V, III, IV

2. Given the following compounds, which will react rapidly with bromine (Br2) at room temperature in the dark?

I II III IV V

A. I, III, V B. II, IV C. III, IVD. I, II, III, IV, V E. II, IV, V

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3. Given the following compounds, which compounds will undergo electrophilic nitration more rapidly than benzene?

I II III IV V VI

A. III, IV, VIB. I, II, VC. I, II, III, VID. II, IV, V E. IV, V, VI

4. Given the following compounds, which compounds give meta substitution under electrophilic bromination conditions?

I II III IV V VI

A. III, IV, VB. I, II, VC. I, II, III, VID. III, IV, VI E. IV, V

5. The first step in the acid-catalyzed hydrolysis of an ester is the addition of an acid which increases the rate of the overall reaction by:

A. protonating the carbonyl-carbon atom thereby making the carbon atom more susceptible to nucleophilic addition.

B. protonating the carbonyl-carbon atom thereby making the carbon atom more susceptible to electrophilic addition.

C. protonating the carbonyl-oxygen atom thereby making the carbon atom more susceptible to nucleophilic addition.

D. protonating the carbonyl-oxygen atom thereby making the carbon atom more susceptible to elecphilic addition.

E. protonating the alkoxy-oxygen thereby making the alcohol part of the ester easier to remove.

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6. The compound below has two aromatic (benzene) rings. The two aromatic rings are different and are labeled A and B. If an electrophilic substitution, such as bromination, is carried out on each compound, from your knowledge of substituent effects, which of the two rings would be preferentially attacked and what would be the orientation of the substituent?

A. Ring A; ortho/para substitutionB. Ring B; ortho/para substitutionC. Ring A; meta substitutionD. Ring B; meta substitution E. Ring B; all sites

7. In the classic reaction of carbonyl compounds, a nucleophile (Z) adds to the carbonyl carbon as shown below:

An sp3 hybridized carbon bonded to an oxygen atom as well as to two electronegative atoms will be unstable. The result will be the following transformation:

A. The π-bond will reform and Y- will be preferentially eliminated if it is a stronger base than Z-.

B. The π-bond will reform and Z- will be preferentially eliminated if it is a stronger base than Y-.

C. The π-bond will reform and both Y- and Z- will be eliminated.D. The π-bond will reform and neither Y- and Z- will be eliminated. E. The π-bond will reform and Y- will be preferentially eliminated if it is a

weaker base than Z-.

8. In the acid-catalyzed formation of an ester, which of the following structures is an intermediate in that reaction?

I II III IV V

A. I B. II C. IIID. IV E. V

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9. Given the following Diels-Alder reaction,

And given below a list of possible structures

I II III IV V

the structure of Compound A is expected to be

A. I B. II C. IIID. IV E. V

10.Ethyl benzoate can be prepared by the Fischer Esterification reaction as shown below by using benzoic acid and ethyl alcohol. A small amount of sulfuric acid is added as a catalyst. You are working for a company where it is desirable to have as high a yield of ethyl benzoate as possible. However, the reaction is an equilibrium reaction and the overall yield of product is somewhat determined by the value of the equilibrium constant, K.

However, the best way to achieve a high yield is by:

A. Adding more of the catalyst, H2SO4. B. Adding an excess amount of ethyl alcohol. C. Adding an excess amount of benzoic acid.D. Adding an excess of ethyl alcohol; carrying out the reaction at less

than 100oC E. Adding an excess of ethyl alcohol; carrying out the reaction at greater

than 100oC

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PART B – Mechanisms and Related Questions (10 marks)

Answer the following three (3) questions. Your answers should be brief and should be specific.

QUESTION B1 (4 marks)Show all the steps in the mechanism for the electrophilic aromatic substitution reaction given below:

Clearly and completely, write each of steps in the boxes below.

STEP 1

STEP 2

STEP 3

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QUESTION B2 (3 marks)

(a) Draw the structure of the product from the following reaction in the box provided.

(b)Show all of the steps in the mechanism for the reaction given above.

B is some base….could be water.

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QUESTION B3 (3 marks)The reaction below shows the addition of HBr to 1-phenylpropene. The only product that is produced is (1-bromopropyl)benzene.

(1-bromopropyl)benzene

(a) Propose a mechanism for the reaction.

(b)Explain (and use appropriate diagrams) why none of the other regioisomer in produced.

Protonation of the double bond at carbon 2 of 1-phenylpropene leads to an intermediate that can be stabilized by resonance involving the aromatic ring. As a result, only one product is formed.

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PART C – Questions on the Synthesis of Organic Compounds (10 marks)

QUESTION C1 (4 marks)The structure of Compound E is shown below. Benzene could be converted into Compound E in four (4) reactions if the reactions are carried out in a proper sequence. If any reaction produces more than one isomer, assume that they are easily separated and you can choose the appropriate isomer to use.

Show how benzene could be converted into Compound E by drawing the reactants (including all reagents) that are required for Reactions A, B, C, and D in the boxes below. Just the basic reagents should be identified…….don’t include any ‘work-up’ reagents such as H3O+.

Compound E

Reaction A Reaction B Reaction C Reaction D

OR

Reaction A Reaction B Reaction C Reaction D

QUESTION C2 (3 marks)Starting from benzene, show how you could legitimately synthesize ONE (1) of the following compounds whose structures are given below. You have access to all inorganic reagents and any organic compound having no more than three carbon atoms.

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The problem that we did in class started with the acylation using acetyl chloride followed by Wolff-Kishner reduction.

Acceptable alternative reactions would Br2/uV rad’n for the bromination and any strong base for the last reaction.

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QUESTION C3 (3 marks)Analyze the following sequence of organic reactions and determine the structure of the final product. Draw the correct structure of the final product in the appropriate box provided. To avoid duplication, in cases where ortho/para directing has resulted in two isomeric compounds, complete the sequence using only the para-isomer. Be certain to consider the regiochemistry and stereochemistry where applicable.

(a)

(b)

(c)

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COMPOUND A

COMPOUND B

COMPOUND C

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