Set4

Chem 210 Training Set IV

All rights reserved: © P. Maslak 2013

Page 1 of 23

Organic Chemistry: Chem 210

Training Set IV

The questions are arranged approximately in the order of the coverage of material in the lecture. This set covers the material of the final exam. Questions 1-50 cover the material of the typical makeup exam.

Notes: I. When listing reagents, a slash (/) is used between reagents that are employed

simultaneously, and a semicolon (;) is used between reagents that are employed in a stepwise fashion.

II. The stereochemistry conventions are illustrated below:

Br

OH

Br

OH

Br

OH

Br

OHNo stereochemistry shown

(all stereoisomers possible) Absolute stereochemistry shown

Relative stereochemistry shown (racemic mixture)

Absolute stereochemistry on one center, unspecified

stereochemistry on the other

III. Abbreviations: Me = methyl, Et = ethyl, Pr = propyl, Bu = butyl, Pe = pentyl, Ph = phenyl (i.e. benzene as a substituent), AcO = acetate (H3CCOO), MCPBA = m-chloroperbenzoic acid., TosO = TsO = tosylate

1. The bond angle in H2O is:

a) 109.5° because the oxygen is sp3 and therefore tetrahedral.

b) 120° because the oxygen is sp2 and therefore flat.

c) Slightly smaller than 109.5° because of increased s character in the lone pairs. d) Larger than 109.5° because the hydrogens want to avoid each other (steric).

2. Which of the following contains at least one sp2

carbon?

a) I only b) I, II, and IV c) I, III, and IV d) II, III, and IV



Page 2 of 23

3. Which orbital of butadiene is involved in the following reaction with HBr? 4. What are the formal charges on the three atoms of ozone in the resonance structure

shown (in order from left to right)?

a) 0, +1, –1 b) +1, 0,–1 c) -1, +1, –1 d) 0, 0, –1

5. Which of the following is not a resonance structure of the others? 6. Which of the following has the lowest barrier to rotation about the indicated bond?



Page 3 of 23

7. A four-bonded carbon atom uses two sp3 and one sp2 hybrids to make three bonds. What is the remaining hybrid that is used to make the fourth bond?

a) pure s e) sp3 b) pure p f) sp4 c) sp g) sp5 d) sp2 h) sp6

i) cannot be determined without knowing the bond angles

8. There are twelve constitutional cycloalkane isomers with a formula C6H12. What is the largest possible number of primary hydrogens in any of these isomers?

a) 3 b) 4 c) 5 d) 6 e) 7 f) 8 g) 9 h) 10 i) 11 j) 12

9. Which of the following conformations has the highest energy? 10. What is the energy difference (in kcal/mol) between the two chair conformations of

the following compound?

a) 2.2 b) 3.2 c) 1.2 d) 0.6 11. Which of the following equilibria has the lowest (smallest) G?



Page 4 of 23

12. Compound A is in equilibrium with which isomer at room temperature? 13. One of the two chair conformations of cis-1-ethyl-3-methylcyclohexane is more

stable than the other by 4.20 kcal/mol. What is the energy cost (in kcal/mol) of 1,3-diaxial interaction between an ethyl and a methyl group?

a) 4.20 b) 2.35 c) 3.25 d) 2.40

14. Even though the rings are of different size, cyclopropane and cyclobutane have

similar overall strain energies. This is because:

a) They have similar angle compression from the optimal 109.5°. b) Strain energies are a kinetic phenomenon (depend on G‡). c) Cyclobutane has more eclipsing interactions, but less angle strain. d) Cyclopropane has a larger overall heat of combustion than cyclobutane.

15. Molecules in sample A are diastereomers of molecules in sample B. Neither sample

shows optical activity in solution. Which of the following statements about them cannot be true?

a) A and B contain cis and trans isomers of the same compound. b) A contains a meso compound, and B contains a racemic mixture. c) Molecules in A have no stereogenic centers, and molecules in B have two

chiral centers related by a symmetry plane. d) Both A and B contain equimolar mixtures of enantiomers.

16. Which of the following compounds are chiral?

a) I only b) III only c) I and II only d) I, II and III



Page 5 of 23

17. Assign stereochemistry to the following compound:

H2N

O

OH

NH2

H2N

12

3

a) 1S, 2S, 3S b) 1S, 2S, 3R c) 1S, 2R, 3R d) 1R, 2S, 3S 18. The structure of E-(S)-1-chloro-1-bromo-2-methyl-2-hexene is best represented by:

a) b) c) d)

19. The following molecule can exist as E, Z isomers. Which isomer is shown?

a) E b) Z

20. How many chiral centers are present in the following molecule?

a) 0 b) 1 c) 2 d) 3 e) 4 f) 5

H CH3

BrH

Cl

CH3

H BrH

Cl

H

CH3

Cl Br

H

H CH3

BrCl

H

F

HO CO2H

O

OCO2H



Page 6 of 23

21. Which of the following reactions is the most exothermic? 22. Which of the following is the worst electrophile? 23. The acid catalyzed reaction of acetaldehyde with methanol involves the following

steps shown below. What is the critical HOMO involved in the first step?

+OHCH3OH

H3CCHH3CCH + H+

O

C

OH

OCH3

H3C

H

+ H+

a) A orbital in acetaldehyde b) s orbital of H+ ion c) orbital in acetaldehyde

d) * orbital in acetaldehyde e) orbital in acetaldehyde f) non-bonded electron pair in acetaldehyde

24. Hyperconjugation is more important for stablizing carbocations than neutral alkenes

because:

a) The carbocation is flat. b) In alkenes, hyperconjugation uses an anti-bonding orbital which partly breaks

the bond. c) There are no empty orbitals on an alkene, so hyperconjugation cannot occur. d) The carbocation is more stable than the alkene.



Page 7 of 23

25. Put the following in order of reactivity with HCl (starting with the least reactive)?

a) I, II, III, IV b) II, I, III, IV c) IV, III, I, II d) II, I, IV, III 26. For the following reaction, which mechanism best describes how this transformation

occurred?

27. Which reaction has the lowest G‡?

H2SO4O

a)H+

OH2 product

b)H+

OH

-H+

product

c)H+

OH-H+

product

d)H+

OH-H+

product

e) H+OH OH

-H+product

OH

-H+

OH



Page 8 of 23

28. Based on the mechanistic arrows in the following sequence, what is the product of this transformation?

H Br

Br Br

Br

Br

Br

A B C D E 29. Where do you expect the best site of protonation for 2-methoxy-butadiene? 30. The product(s) of the following reaction can best be described as:

a) a racemic mixture b) a single enantiomer c) a pair of diastereomers d) an achiral molecule.

31. Which of the following carbocations would not likely rearrange to a more stable

carbocation?



Page 9 of 23

32. Electrophilic addition of HBr to an alkene can best be characterized as:

a) Anti-Markovnikov b) Anti-addition. c) Syn-addition d) None of the above.

33. Which of the following compounds was the starting material for the oxidation shown

below?

KMnO4/H+

O

OHO

OH

O

+ CO2

A B C D 34. Rank the alkenes below from most stable to least stable:

A B C

a) A>B>C b) B>A>C c) C>A>B d) B>C>A e) C>B>A 35. What is the degree of unsaturation for: C6H8FN?

a) 2 b) 3 c) 4 d) 5 36. Which conditions would you use to perform the following transformation?



Page 10 of 23

37. Which of the listed molecules is the product of the following reaction? 38. What will be the products of the following reaction?

a) II and III b) III and IV c) I and IV d) I, II, III, and IV 39. Consider the following synthesis. What is wrong with these transformations?

H2O/Hg2+/H2SO4

NaOEt;CH3I

O

CH3

a) The keto form of the final enol product actually forms the more substituted

ketone. b) The starting material only consists of a five-carbon chain while the final

product contains a six-carbon chain. c) The sulfuric acid present in the second set of reagents cleaves the triple bond. d) The acetylide anion cannot form because ethoxide is not strong enough to

deprotonate the alkyne. e) The reagents in the first step yield a compound with both an alcohol and

halide functional group.



Page 11 of 23

40. What is the best route to synthesize (1-bromoethyl)benzene from ethylbenzene?

a) HBr in ether b) Br2/CCl4 c) NBS/H2O/DMSO d) NBS/CCl4/h e) NaNH2/NH3/CH3Br

41. The product of the following set of reactions forms through a bromonium ion

intermediate in the second step. What is the major organic product of these reactions?

cyclohexeneNBS

CCl4/h1.

HBr product2.

a) trans-1,2-dibromocyclohexane b) cis-1,2-dibromocyclohexane c) trans-1,3-dibromocyclohexane d) cis-1,3-dibromocyclohexane

42. The wavelength of light absorbed by a conjugated system of double bonds depends

on:

a) the difference in energy between HOMO and LUMO. b) the energy of the HOMO. c) the energy of the LUMO. d) the amount of aromatic stablization.

43. Rank the free radicals below from the most stabilized to the least stabilized:

A. B. C. D.

a) A>C>B>D b) C>A>B>D c) C>D>A>B d) A>D>C>B e) D>A>C>B



Page 12 of 23

44. Compound A could react to form compound B or C as shown in the reaction diagram below. Which of the following is true?

a) Compound C will be the major product under kinetic conditions. b) Compound B will be the major product under thermodynamic conditions. c) Compound C will always be the major product because it has the lowest

energy. d) Compound B will be the major product at low temperatures.

45. Which of the following is not aromatic? 46. Which of the following reactions is the most exergonic?



Page 13 of 23

47. 1,3,5,7-Cyclononatetraene can be converted to an aromatic substance by: a) hydrogen atom abstraction b) hydride abstraction c) proton abstraction d) H2 elimination e) it cannot be converted to an aromatic compound

48. The radical chain reaction of Cl-Br with 2,3-dimethylbutane gives a mixture of

products. Which products (and in what ratio) are formed?

49. What is the most likely product of the following reaction?

Br

Br=

1600

6

6

5=

Br

Br

6

1600=

Cl

Cl

6=

Cl

Cl5

a)

b)

c)

d)



Page 14 of 23

50. 1-Fluorobutane undergoes free-radical chlorination with Cl2. Including stereoisomers, how many mono-chlorinated substitution products will form?

a) 2 b) 3 c) 4 d) 5 e) 6 f) 7 g) 8

51. According to MO theory, SN2 reactions occur by backside displacement of the

leaving group with the nucleophile because: a) the shape of the HOMO of the nucleophile makes any other displacement

impossible. b) the HOMO - LUMO gap is the smallest. c) the LUMO of the electrophile must donate electrons into the HOMO of the

nucleophile. d) the shape of the LUMO of the electrophile controls the side of attack.

52. Consider the rate equation of the following reaction. How would the rate be effected

if the concentration of KCN were doubled?

a) No effect b) The rate would double. c) The rate would be halved. d) It depends on the concentration of starting material (chloropropane).

53. Consider the following reaction:

Which type of reaction mechanism best explains what has occurred? a) E1 f) SN1 with a 1,2-hydride shift b) E2 g) SN2 with a 1,2-hydride shift c) SN1 h) E2 with a 1,2-hydride shift d) SN2 i) SN1 with a 1,2-methyl shift e) E1 with a 1,2-hydride shift j) E1 with a 1,2-methyl shift 54. Which of the following is the most nucleophilic?

Br OH

( R )-2-bromo-3-methylbutane 2-methyl-2-

H2O



Page 15 of 23

55. Which of the following is the best nucleophile? 56. What is the major product of the following reaction?

a) 2-methyl-1-butene b) 2-methyl-2-butene c) 2-hydroxy-2-methylbutane d) 2-hydroxy-3-methylbutane

57. The following reaction will likely follow which mechanism?

a) E1 b) E2 c) SN1 d) SN2 58. Which of the following SN2 reactions would be the fastest? 59-62. For each of the following pairs of SN2 reactions, decide which one occurs with the

larger rate constant?

59 a) Br + H2O or b) Br + HO

60 + HOBr

c) or + HOBr

d)

61 e) Cl + CH3O or f) Cl + CH3S 62 g) Cl + CN or h) I + CN



Page 16 of 23

63. Consider the following E1/SN1 reaction.

The major missing product(s) is (are):

a) A b) B c) C d) D

e) A and B f) C and D g) B and C h) A, B, C, and D 64. What is the product of the following SN2 reaction?

Ph

O

OCH3

TosONaBr

DMSO

Ph

O

OCH3

Br

Ph

O

OCH3

Br

Ph

O

OCH3

Br

Ph

O

OCH3

Br

a) b) c) d) 65. The following rate equation corresponds to which reaction mechanism?

a) E1 b) E2 c) SN1 d) SN2

Br

H

CH3

H3C

H2OEthanol /

OH

HH3C

CH3CH3

H3CH

+

H

OH

H3C

CH3

H3CH

HCH3

CH3

H3CH

CH3

A B C D



Page 17 of 23

66. Which will be the major product of the following E2 reaction? 67. Consider the energy diagram for the two step E1 reaction. The transition state of the

slowest step (rate determining step) most resembles:

a) the starting material b) the carbocation c) the product d) none of the above since the starting material and product have similar energies

68. Which of the following molecules has the lowest pKa? 69. Which reaction conditions would be best to perform the following transformation?



Page 18 of 23

70. Which HOMO and LUMO are involved in the following aromatic substitution? 71. Which reaction conditions would be best to perform the following transformation? 72. Which would not be a good method to prepare compound A?



Page 19 of 23

73. Which reaction conditions would be best to perform the following transformation?

CH3

OCH3

Br

a) NBS/CH3OH b) OsO4/NaHSO3; HBr; NaOH; CH3I c) MCPBA; HBr; NaOH, CH3I d) Br2; CH3O

–Na+ e) HBr/CH3OH

74. What is the major product of the following reaction?

O 1. CH3CH2MgBr

2. H3O+

OH OHOH OH

a) b) c) d)

OH

e)



Page 20 of 23

Total Strain Energies in Cycloalkanesring size kJ/mol kcal/mol

3 115 27.6 4 110 26.4 5 27 6.5 6 0 0 7 26 6.3 8 40 8.6

Energy Costs for Interactions in Alkane Conformers

Interaction kJ/mole kcal/mole H-H eclipsed 4.0 1.0

H-CH3 eclipsed 6.0 1.4

CH3-CH3 eclipsed 11.0 2.6

CH3-CH3 gauche 3.8 0.9



Page 21 of 23

Selectivity of halogen radicals (per H)

3o 2o 1o

F· 2 1 1 Cl· 5 3.5 1 Br· 1600 80 1 I· 97000 1100 1



Page 22 of 23



Page 23 of 23

Answer key: Set IV

1. C 2. C 3. A 4. A 5. C 6. C 7. G 8. G 9. A 10. C 11. C 12. C 13. B 14. C 15. C 16. C 17. A 18. D 19. A 20. D 21. C 22. C 23. F 24. B 25. A 26. D 27. D 28. A 29. A 30. C 31. B 32. D 33. A 34. E 35. B 36. C 37. C 38. C 39. D 40. D 41. A 42. A 43. A 44. D 45. D

46. B 47. C 48. C 49. D 50. F 51. D 52. B 53. F 54. B 55. C 56. B 57. D 58. C 59. B 60. C 61. F 62. H 63. E 64. A 65. B 66. D 67. B 68. B 69. C 70. A 71. A 72. B 73. A 74. A

Set4

Documents

training set

carbon chain

strain energies

rights reserved

hydride shift

och3 ph

cl br

br br