qoi 0809 e1 e2 - ualgw3.ualg.pt/~abrigas/qoi0809t1_elimina.pdf · · 2008-10-09qoi 0809 e1 e2...

QOI 0809 E1 E2

Name___________________________________

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

1) Which of the following are the elimination products of the reaction shown below?

CH3CH2Br + -OH → ?

A) CH3CH2Br+H + O-

B) HOCH2CH2Br

C) CH3CH2OH + Br-

D) CH2CH2 + Br- + H2O

E) CH2CHBr + H2O

1)

SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.

2) Draw the alkene product which results when 1-bromopentane is heated in acetone

containing NaOH. Give a detailed, step-by-step mechanism for the production of this

compound.

2)


3) Which of the following compounds undergoes E2 reactions with the fastest rate?

A)

B) CH3CH2CH2Cl

C) CH3CH2CH2I

D)

E) CH3CH2CH2Br

3)

1

4) Which of the following bases gives the highest anti-Zaitsev product in E2 reactions when reacted

with 2-bromo-2, 3-dimethylbutane?

A)

B)

C)

D)

E)

4)

2

5) What is the major product of the following E2 reaction?

A)

B) CH3CH2CHCH2

C)

D)

E)

5)

6) How many distinct alkene products are possible when the alkyl iodide below undergoes E2

elimination?

A) 1 B) 2 C) 3 D) 4 E) 5

6)

7) Which of the alkyl chlorides listed below undergoes dehydrohalogenation in the presence of a

strong base to give 2-pentene as the only alkene product?

A) 1-chloropentane

B) 2-chloropentane

C) 3-chloropentane

D) 1-chloro-2-methylbutane

E) 1-chloro-3-methylbutane

7)

3

8) When 2-bromo-3-methyl-1-phenylbutane is treated with sodium methoxide, why is the major

product 3-methyl-1-phenyl-1-butene?

A) SN2 predominates over E2.

B) E1 predominates over E2.

C) The bulkiness of the methoxide results in the less substituted alkene.

D) The newly formed double bond in this compound is conjugated with the phenyl ring.

E) The less substituted alkene is always more stable than the more substituted alkene.

8)

9) What is the major organic product of the following reaction?

A) 2,3-dimethyl-1-hexene

B) 2,3-dimethyl-2-hexene

C) 2-isopropyl-1-pentene

D) (Z)-2,3-dimethyl-3-hexene

E) (E)-2,3-dimethyl-3-hexene

9)

10) What is the major organic product of the following reaction?

A) 2,3-dimethyl-1-hexene

B) 2,3-dimethyl-2-hexene

C) 2-isopropyl-1-pentene

D) (Z)-2,3-dimethyl-3-hexene

E) (E)-2,3-dimethyl-3-hexene

10)

11) Which of the following halides is most reactive in an E2 reaction with sodium methoxide?

A) (CH3)3CCH2I

B) (CH3)2CHCHICH3

C) (CH3)2CHCH2Br

D) (CH3)2CHCH2Cl

E) (CH3)2CHCH2CH2Cl

11)

12) Which of the following halides is least reactive in an E2 reaction with sodium methoxide?

A) (CH3)3CCH2I

B) (CH3)2CHCHICH3

C) (CH3)2CHCH2Br

D) (CH3)2CHCH2Cl

E) (CH3)2CHCH2CH2Cl

12)

4

13) Which of the following statements is true concerning the E2 reactions of alkyl fluorides?

A) Alkyl fluorides react more readily in E2 reactions than do alkyl iodides.

B) The transition state of this E2 reaction resembles a carbanion rather than an alkene.

C) The C-F bond is the weakest carbon-halogen bond so SN2 will always predominate over E2

in the reactions of alkyl fluorides.

D) Alkyl fluorides react to form the most stable carbocation intermediate.

E) Alkyl fluorides cannot adopt the proper stereochemical alignment for an E2 reaction to occur.

13)


14) When 1-iodo-1-methylcyclohexane is treated with NaOCH2CH3, the more highly

substituted alkene product predominates. When KOC(CH3)3 is used instead, the less

highly substituted alkene product predominates. Offer an explanation.

14)

15) Provide the structure of the major organic product which results when

2-bromo-2-methylbutane is treated with sodium ethoxide.

15)

16) Draw all likely alkene products in the following reaction and circle the product you expect

to predominate.

16)


to predominate.

17)


to predominate.

18)

5

19) Supply the missing alkyl halide reactant in the elimination reactions shown below. 19)

20) Provide the structure of the major organic product of the following reaction. 20)


6


22) Which of the following alkyl halides undergoes E1 reactions with the fastest rate?

A)

B)

C)

D)

E) CH3I

22)

23) Which of the following alkyl halides forms the most stable carbocation when it undergoes an E1

reaction?

A) I B) II C) III D) IV E) V

23)

24) Which of the following statements correctly describe(s) E1 reactions of alkyl halides (RX)?

I. Rate = k[base]

II. Rate = k[base][RX]

III. Rate = k[RX]

IV. The reactions occur in two distinct steps.

V. Rearrangements are sometimes seen.

A) II and IV

B) III and V

C) I, IV, and V

D) I only

E) III, IV, and V

24)

7

25) Consider the following experimental data for the rate of the reaction given below:

Experiment #1 [Alkyl Halide] [Base] Rate

1 0.01 0.01 1

2 0.02 0.01 2

3 0.01 0.02 1

What is the mechanism for the reaction?

A) first order, SN1

B) first order, SN2

C) first order, E1

D) first order, E2

E) none of the above

25)

26) Which of the following correctly reflects relative stabilities of carbocations?

A) 3° allylic > 2° > 1° benzylic

B) methyl > 2° benzylic > 3°

C) 3° benzylic > vinyl > 1°

D) 2° allylic > 2° > vinyl

E) 1° benzylic > 3° > 3° allylic

26)


27) When 1-bromo-2, 2-dimethylcyclopentane is heated in ethanol, one of the products which

results is shown below. Provide a detailed, stepwise mechanism for the production of this

compound, and give the name of the mechanism by which it is produced.

27)

28) List the following compounds in order of increasing reactivity in an E1 elimination.

CH3CH2CHBrCH3, CH3CH2CH2CH2Br, (CH3)3CBr

28)


29) Dehydrohalogenation of 2-bromobutane in the presence of a strong base proceeds via which of the

following mechanistic pathways?

A) SN1

B) SN2

C) E1

D) E2

E) none of the above

29)

8


30) Provide the structure of the major organic product in the following reaction. 30)

31) Why is the E1 not a likely mechanism when 1-chloropentane is heated in ethanol? 31)


32) Which of the following is least likely to be found in the product mixture which results when

2-iodopentane reacts with sodium ethoxide in ethanol?

A) 1-ethoxypentane

B) 2-ethoxypentane

C) (Z)-2-pentene

D) (E)-2-pentene

E) 1-pentene

32)

33) What is the major product which results when (2R,3S)-2-chloro-3-phenylbutane is treated with

sodium methoxide in methanol?

A) (E)-2-phenyl-2-butene

B) (Z)-2-phenyl-2-butene

C) (S)-3-phenyl-1-butene

D) (R)-3-phenyl-1-butene

E) (R)-2-methoxy-2-phenylbutane

33)

34) Why is the alkyl halide below not capable of undergoing an E2 reaction upon treatment with

sodium ethoxide?

A) Br- is too poor a leaving group.

B) The substrate is too hindered.

C) Too much angle strain would be present in the alkene product.

D) Sodium ethoxide is a poor base to use in E2 reactions.

E) The C-H and C-Br bonds which need to break cannot achieve an anti-periplanar orientation.

34)

9

35) Which of the compounds shown below is/are the product(s) of this reaction:

A) I only

B) II only

C) I and II are of equal yield.

D) I is major, II is minor.

E) I is minor, II is major.

35)

36) Which of the following compounds is/are the products of this reaction:

A) I only

B) II only

C) I and II are of equal yield.

D) I is major, II is minor.

E) I is minor, II is major.

36)


37) Provide the structure of the major organic product which results in the following reaction. 37)

10


39) Which diastereomer of 1-bromo-4-t-butylcyclohexane, the cis or the trans, undergoes

elimination more rapidly when treated with sodium ethoxide? Explain your answer.

39)


41) Provide the structure of the major elimination product which results when the alkyl

bromide below is heated in ethanol.

41)


42) A primary kinetic isotope effect could most likely be observed in which of the following

mechanisms?

A) SN1 and SN2

B) SN2

C) E1 and SN1

D) E2

E) E1

42)

11

43) What is the major product of the following reaction?

A) CH2CHCH2CH3

B) CH3CHCHCH3

C)

D) CH3CH2CH2CH2OCH2CH3

E)

43)


A) CH2CHCH2CH3

B) CH3CHCHCH3

C)

D) CH3CH2CH2CH2OCH2CH3

E)

44)

12



45)

46) What is/are the product(s) of the following reaction?

A)

B) CH2CH2

C)

D) A and B

E) A and C

46)

47) Predict the two most likely mechanisms for the reaction of 2-iodohexane with sodium ethoxide.

A) SN2 and SN1

B) E1 and E2

C) SN2 and E2

D) E1 and SN1

E) E2 and SN1

47)

13

48) Predict the two most likely mechanisms which occur when 2-iodohexane is heated in ethanol.

A) SN2 and SN1

B) E1 and E2

C) SN2 and E2

D) E1 and SN1

E) E2 and SN1

48)

49) What is/are the product(s) of the following reaction?

A)

B) CH2CH2

C)

D) A and B

E) A and C

49)

50) What mechanism predominates in the reaction below?

A) SN2

B) SN1 without rearrangement

C) SN1 with rearrangement

D) E2

E) E1

50)

14


A) SN2



D) E2

E) E1

51)


A) SN2



D) E2

E) E1

52)

53) Which of the following is least likely to be found in the product mixture which results when the

alkyl iodide below is heated in water?


53)


54) Which base, ammonia (NH3) or triethylamine [(CH3CH2)3N], would be a better choice for

use in converting 1-chlorohexane to 1-hexene? Explain briefly.

54)

15


56) Can primary alkyl halides react by SN2, SN1, E2, and E1 mechanisms? Are any of these

mechanisms prohibited? What conditions favor a particular mechanism?

56)

57) What reaction mechanism predominates when 1-bromo-1-propylcyclopentane is treated

with sodium methoxide in methanol?

57)

58) What reaction mechanism predominates when 1-bromo-1-propylcyclopentane is heated

in ethanol?

58)

59) Provide the major organic product(s) in the reaction below. 59)


60) Starting with 2-butene, which of the following is the best method for preparing 2-butyne?

A) HBr; H2/Ni; Zn/H+

B) HBr; Zn/H+; H2/Ni

C) Br2/CCl4; Zn/H+; H2/Ni

D) Br2/CCl4; 2NaNH2

E) HBr; NaNH2

60)


61) Which of the following alkyl chlorides would undergo substitution most rapidly when

treated with NaCCH: chloroethane, 2-chloropropane, or 1-chloro-2, 2-dimethylpropane?

Provide the structure of the substitution product.

61)

62) Show the best way to prepare CH3OCH(CH3)2 by an SN2 reaction. 62)

16

63) Write the structures for the products of the following SN2 reactions. 63)



A) CH2 CHCH2CH CH2

B)

C) CH2 CHCH CHCH3

D)

E) CH2 CHCH2CH2 CH2OH

64)

65) Which sequence of reagents works best to convert 3-hexene to 3-hexyne?

A) 1. HCl 2. NaNH2

B) 1. BH3·THF 2. HO-, H2O2 3. NaNH2

C) 1. NaNH2 2. HI 3. H3O+

D) 1. Br2, CH2Cl2 2. NaNH2 (excess)

E) 1. Cl2, CH2Cl2 2. NaCN (excess)

65)

66) Which sequence of reagents works best to convert 1-bromobutane to hexane?

A) 1. NaOCH3, CH3OH 2. NaCN 3. Na, NH3

B) 1. NaC≡CH 2. H2 (excess), Pd/C

C) 1. CH3CH2OH, delta 2. H2 (excess), Pd/C

D) 1. NaCN 3. BH3*THF 4. HO-, H2O2

E) 1. NaC≡CCH2CH3 2. Na, NH3

66)

17




18

Answer KeyTestname: UNTITLED1

1) DID: oc5b 9-1Diff: 0Skill:

2)

ID: oc5b 9-2Diff: 0Skill:


4) EID: oc5b 9-4Diff: 0Skill:

5) CID: oc5b 9-5Diff: 0Skill:




9) BID: oc5b 9-9Diff: 0Skill:



12) AID: oc5b 9-12Diff: 0Skill:

19



14) The unhindered ethoxide produces the more stable alkene product (ie, the more highly substituted alkene possible).

When the bulky t-butoxide is used, the most accessible hydrogen is removed. This results in the least highly

substituted alkene possible.ID: oc5b 9-14Diff: 0Skill:

15)


16)


17)


20


18)


19) a) bromomethylcyclohexane

b) CH3CH2CHBrCH2CH3

c) CH3CH2CH(CH3)CH2Br


20)


21)



21






27)


28) CH3(CH2)3Br < CH3CH2CHBrCH3 < (CH3)3CBr



22


30)


31) Primary halides cannot undergo E1 reactions because of the difficulty encountered in forming primary carbocations.ID: oc5b 9-31Diff: 0Skill:






37)


38)


23


39) The cis isomer reacts more quickly. An axial orientation of the C-Br bond is required for E2 in six-membered ring

systems. In order for this to occur in the trans isomer, the bulky t-butyl group must also assume an axial orientation;

this requires substantial energy of activation.ID: oc5b 9-39Diff: 0Skill:

40)


41)








24








54) Triethylamine. Amines can serve as both nucleophiles and as bases in reactions with alkyl halides. Increasing the steric

bulk about the nitrogen diminishes the nucleophilicity while allowing the amine to continue to function effectively as a

base.ID: oc5b 9-54Diff: 0Skill:

55)


56) Only SN2 and E2 pathways are available to primary halides. SN1 and E1 cannot occur due to the instability of primary

carbocations. SN2 will typically predominate over E2 unless there is steric hindrance in the alkyl halide or

nucleophile/base.ID: oc5b 9-56Diff: 0Skill:

57) E2ID: oc5b 9-57Diff: 0Skill:

25


58) SN1


59)



61) Chloroethane reacts most rapidly; CH3CH2CCH is produced.


62) CH3I + NaOCH(CH3)2ID: oc5b 9-62Diff: 0Skill:

63) a) 3-cyclopentyl-1-propyne

b) 2-iodo-4-methylpentane

c) 1-methoxypropaneID: oc5b 9-63Diff: 0Skill:




67)


26


68)


27

qoi 0809 e1 e2 - ualgw3.ualg.pt/~abrigas/qoi0809t1_elimina.pdf · · 2008-10-09qoi 0809 e1 e2...

Documents