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

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1 Exam Name MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) Which of the following statements is incorrect about benzene? 1) A) All of the carbon atoms are sp hybridized. B) The carbon-carbon bond lengths are all the same. C) It has delocalized electrons. D) The carbon-hydrogen bond lengths are all the same. E) All twelve atoms lie in the same plane. A 2) Which of the following statements about benzene is correct? 2) A) The carbon-carbon bond length is longer than that of ethane. B) It is a planar molecule. C) All of the carbon atoms are sp3 hybridized. D) The carbon-hydrogen bonds are not the same length. E) It has no delocalized electrons. B 3) The delocalized system in benzene is formed by a cyclic overlap of 6 orbitals. 3) A) p B) sp2 C) sp3 D) sp E) s A 4) Which of the following pairs are resonance structures? 4) A) I B) II C) III D) IV E) V C 1

2 5) Which of the following pairs are resonance structures? 5) A) I B) II C) III D) IV E) V C 6) Which of the following is not a resonance structure of the species shown? 6) A) I B) II C) III D) IV D 2

3 7) In which of the following does resonance delocalization of electron density not play a role? 7) A) benzyl anion B) allyl cation C) CO3 2- D) cyclohexyl radical E) O3 D 8) Due to electron delocalization, one would predict that the carbon-oxygen bond in acetamide, CH3CONH2,. 8) A) is longer than the carbon-oxygen bond of dimethyl ether, (CH3)2O B) is formed by overlapping sp3 orbitals C) has more double bond character than the carbon-oxygen bond of acetone, (CH3)2CO D) is nonpolar E) is longer than the carbon-oxygen bond of acetone, (CH3)2CO E SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 9) Draw two other resonance contributors for the following compound: 9) 10) Are the following pairs of structures resonance contributors or different compounds? 10) They are resonance contributors. 11) Draw the important resonance structures of: 11) H C N N: 3

4 12) Draw the important resonance structure of: 12) 13) Draw the important resonance structures of: 13) 14) Draw the important resonance contributing forms for the structure shown below. 14) 4

5 15) Draw the important resonance contributing forms for the structure shown below. 15) 16) Draw the important resonance contributing forms for the structure shown below. 16) 17) Mark the most electron-rich carbon atom in the compound below with an asterisk. 17) CH 3 CH=CHNHCH 3 5

6 18) Draw all major resonance contributors of the species below. 18) 19) Draw all major resonance contributors of the species below. 19) 6

7 20) Draw all major resonance contributors of the species below. 20) 21) Draw all major resonance contributors of the species below. 21) 7

8 22) Provide the major organic product of the following reaction. 22) 23) Provide the major organic product of the following reaction. 23) 8

9 24) Which of the following is the strongest acid? 24) 9

10 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 25) Which of the following is the most stable resonance contributor to acetic acid? 25) A) B) C) D) E) B 10

11 SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 26) Draw four resonance contributors for the following structure and indicate which is the most important contributor. Explain. 26) C is the most important contributor because all the atoms have complete octets and the negative charges are on the most electronegative atoms. 27) Rate the following molecules in decreasing order of stability: 27) a > c > b aromatic > linear > antiaromatic 28) Stabilization of a charged species usually results when this species can be more accurately depicted as a hybrid of several resonance contributing forms. Why is this the case? 28) Stabilization results from delocalization of charge. 29) In the acetate ion (CH3CO2 - ), which of the oxygen atoms bears a greater negative 29) charge? Explain your answer. The acetate ion is a hybrid of the two resonance contributors below. Each oxygen in this ion has the same charge (-1/2); the oxygen atoms are indistinguishable and the carbon-oxygen bonds are identical. 11

12 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 30) Which of the following statements concerning resonance contributors and resonance hybrids is not correct? A) The greater the number of relatively stable resonance contributors, the greater the resonance energy. B) The greater the predicted stability of a resonance contributor, the more it contributes to the resonance hybrid. C) A resonance hybrid is more stable than the predicted stability of any of its resonance contributors. D) The fewer nearly equivalent resonance contributors are in the structure, the greater the resonance energy. E) none of the above 30) D SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 31) What is suggested by the fact that benzene's molar heat of hydrogenation is 36 kcal less than three times the molar heat of hydrogenation of cyclohexene? 31) This suggests that the type of bonding in benzene lends special stability to the molecule. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 32) Which of the following is an allylic cation? 32) A) I B) II C) III D) IV E) V B 12

13 33) Which of the following is a benzylic cation? 33) A) I B) II C) III D) IV E) V D 34) Which of the following is the most stable cation? 34) A) I B) II C) III D) IV E) V C 35) How many allylic hydrogen atoms are present in the following molecule? 35) A) 2 B) zero C) 5 D) 3 E) 4 B 36) How many benzylic hydrogens are present in the following molecule? 36) A) 2 B) 3 C) 5 D) zero E) 4 D 13

14 37) Which of the following is the most stable diene? 37) A) I B) II C) III D) IV E) V C 38) Which of the following compounds contains the longest carbon-carbon single bond? 38) A) 1, 3-butadiyne B) 1, 3-butadiene C) propyne D) ethane E) allene D 39) What is the hybridization of the central carbon of allene (1,2-propadiene)? 39) A) sp B) p C) sp2 D) sp3 E) none of the above A 40) What descriptive term is applied to the type of diene represented by 2,4-hexadiene? 40) A) cumulated diene B) alkynyl diene C) conjugated diene D) isolated diene E) none of the above C 41) What descriptive term is applied to the type of diene represented by 1, 5-octadiene? 41) A) alkynyl diene B) conjugated diene C) cumulated diene D) isolated diene E) none of the above D 14

15 42) Which of the following is a cumulated diene? 42) A) I B) II C) III D) IV E) V C 43) Which of the following is a conjugated diene? 43) A) I B) II C) III D) IV E) V A SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 44) Which of the following numbered hydrogens is most easily abstracted by heterolytic cleavage? Explain. 44) Hydrogen #3 is most easily abstracted by heterolytic cleavage because the carbocation produced from the cleavage is allylic. 45) Which of the following compounds is more stable? Explain. 45) (a) and (b) are both benzylic cations. (b) is more stable because it is more alkyl substituted. 46) Rank the following dienes in order of increasing stability: trans-1, 3-pentadiene, cis-1, 3-pentadiene, 1, 4-pentadiene, and 1, 2-pentadiene. 46) 1, 2-pentadiene < 1, 4-pentadiene < cis-1, 3-pentadiene < trans-1, 3-pentadiene 15

16 47) Among a series of isomeric trienes, the more negative the H of the hydrogenation reaction of a given triene, the stable it is relative to the others in the isomeric series. 47) less 48) Consider the hydrogenation reaction of each compound listed and rank the compounds in order of increasing H of this reaction. The most negative H should be listed first. cis-2-pentene, 2, 3-pentadiene, and trans-1, 3-pentadiene 48) 2, 3-pentadiene < trans-1, 3-pentadiene < cis-2-pentene 49) Consider the hydrogenation reaction of each compound listed and rank the compounds in order of increasing H of this reaction. The most negative H should be listed first. 49) 2, 5-dimethyl-1, 3-cycloheptadiene, 1, 4-dimethyl-1, 3-cycloheptadiene, and 3, 6-dimethyl-1, 4-cycloheptadiene 3, 6-dimethyl-1, 4-cycloheptadiene < 2, 5-dimethyl-1, 3-cycloheptadiene < 1, 4-dimethyl-1, 3-cycloheptadiene 50) Arrange the following unsaturated hydrocarbons in order of decreasing reactivity toward HBr addition: 50) III > II > IV > I MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 51) In the molecular orbital representation of benzene, how many molecular orbitals are present? 51) A) 4 B) 1 C) 8 D) 2 E) 6 E 16

17 52) Which species is represented by the following distribution of electrons in the molecular orbitals and energy levels diagram? 52) A) I B) II C) III D) IV E) V C 53) Excluding the horizontal node which is coincident with the molecular plane, how many nodes are present in 4 of the 1, 3, 5-hexatriene system? 53) A) 3 B) 6 C) 0 D) 5 E) 4 A SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 54) Provide a diagram which depicts the relative energies of the molecular orbitals of benzene. Show which molecular orbitals are filled in benzene's ground state. 54) 55) Show how the p orbitals overlap to form the nonbonding molecular orbital of the allyl system. 55) 56) Which MOs are bonding MOs in the ground state of 1,3,5-hexatriene? 56) 1, 2, 3 17

18 57) Draw the LUMO of 1,3,5-hexatriene. 57) 58) Draw the HOMO of 1,3,5-hexatriene. 58) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 59) Which of the following is/are the major product(s) of the following reaction? 59) A) II B) I and II C) III D) I E) I and III D 60) Which of the following is the strongest acid? 60) A) B) C) CH3OCH3 D) CH3CH2OH E) B 18

19 61) Which of the following is the strongest acid? 61) A) I B) II C) III D) IV E) V D 62) Which of the following ions is most acidic? 62) A) C6H5CH2NH3 + B) CH3CH2NH3 + C) CH3NH3 + D) C6H5NH3 + E) (CH3)2CHNH3 + D 63) Which of the following is the weakest base? 63) A) phenolate ion (C6H5O-) B) ethoxide ion (CH3CH2O-) C) acetate ion (CH3CO2 - ) D) methoxide ion (CH3O-) E) hydroxide ion (HO-) C 19

20 SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 64) Provide the structure of the major organic product(s) in the reaction below. 64) 65) Why is phenol a stronger acid than cyclohexanol? 65) The anion of phenol is stabilized by resonance, causing the proton to be more easily abstracted than that of cyclohexanol. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 66) Which of the following is/are the main product(s) of the following reaction? 66) CH 2 CH CH CH 2 A) HBr? B) C) D) A and B E) A and C E 20

21 67) What is/are the product(s) from the following reaction? 67) A) I only B) II only C) equal amounts of I and II D) I is major, II is minor E) I is minor, II is major D 68) What is/are the product(s) of the following reaction? 68) A) I only B) II only C) III only D) I and II E) I and III E 69) What compound results from the 1, 4-addition of one equivalent of HBr to 1, 3-butadiene? 69) A) 4-bromo-1-butene B) 2-bromo-2-butene C) 1-bromo-2-butene D) 1-bromo-1-butene E) 3-bromo-1-butene C 21

22 70) Which of the following is/are the major product(s) of the following reaction? 70) A) I B) II and III C) I and III D) III E) II E 71) What is/are the product(s) from the following reaction? 71) A) I and IV B) II and III C) II and IV D) I and II E) I and III D SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 72) Provide the structure of the major organic product(s) in the reaction below. 72) 22

23 73) Provide the structure of the major product which results from 1, 2-addition of HBr to the diene shown below. 73) 74) Provide the structure of the major product which results from 1, 4-addition of Br2 to 74) the diene shown below. 23

24 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 75) What is the thermodynamic product for the following reaction? 75) A) I B) II C) III D) IV E) V D 24

25 76) What is the kinetic product for the following reaction? 76) A) I B) II C) III D) IV E) V E 77) Which of the following is a correct statement considering thermodynamic versus kinetic control of organic reactions? A) When a reaction is under thermodynamic control, the relative amounts of products depend on the activation energies of the steps leading to their formation. B) Higher temperatures and longer reaction times typically favor the kinetic product over the thermodynamic product. C) When the products are in equilibrium under the reaction conditions, the relative amounts of products depend on their stabilities and the reaction is under thermodynamic control. D) The kinetic product always predominates when the reaction is reversible. E) none of the above 77) C 25

26 78) What is/are the product(s) from the following reaction? 78) A) II Major, III Minor B) II Minor, III Major C) III only D) I and II E) II and III A 79) What is/are the product(s) from the following reaction? 79) A) I only B) II only C) III only D) II and III E) I and II C SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 80) What is the major product obtained from the addition of one mole of HCl at high temperature to 1, 3-butadiene? 80) 1-chloro-2-butene (thermodynamic product) 26

27 81) Draw the structure of the major product which results when the diene shown is treated with HBr at 40 C. 81) 82) Draw the structure of the major product which results when the diene shown is treated with HBr at -80 C. 82) 83) In the addition of HBr to conjugated dienes, is the product which results from 1, 2-addition or that which results from 1, 4-addition typically the product of kinetic control? 83) The product of kinetic control typically results from 1, 2-addition. 27

28 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 84) What is the product of the following reaction? 84) A) I B) II C) III D) IV E) V E 85) What is the product from the following reaction? 85) A) I B) II C) III D) IV E) V B 28

29 86) Which of the following conjugated dienes would not react with a dieneophile in a Diels-Alder reaction? 86) A) I B) II C) III D) IV E) I and III E 87) Which of the following dienes is the most reactive in a Diels-Alder reaction? 87) A) I B) II C) III D) IV E) V C 29

30 88) What diene and what dieneophile would be used to synthesize the following compound? 88) A) I B) II C) III D) IV E) V B 89) Which of the following terms best describes a Diels-Alder reaction? 89) A) a 1, 3-dipolar cycloaddition B) a sigmatropic rearrangement C) a [4+2] cycloaddition D) a [2+2] cycloaddition E) a substitution reaction C 90) When 1, 3-butadiene reacts with CH2 CHCN, which of the terms below best describes the 90) product mixture? A) a single compound B) a mixture of bicyclic compounds C) a racemic mixture D) a mixture of two diastereomers E) optically active C 91) The Diels-Alder reaction is a concerted reaction; this means: 91) A) the reaction follows Markovnikov's rule. B) a mixture of endo and exo products is formed. C) all bond making and bond breaking occurs simultaneously. D) the products contain rings. E) the reaction is highly endothermic. C 30

31 92) Which of the following statements is (are) true of the Diels-Alder reaction? 92) A) Secondary orbital interactions typically cause the endo product to be favored kinetically over the exo. B) Substituents which are cis in the dienophile remain cis in the product. C) When the diene is electron-rich, the reaction works best when the dienophile contains one or more electron-withdrawing groups conjugated to its C C. D) Dienes which cannot achieve an s-cis conformation do not react in Diels-Alder reactions. E) all of the above E 93) When 1, 3-cyclopentadiene reacts with the cis-isomer of NCCH=CHCN, the major product is. A) optically active B) a meso compound C) a fused bicyclic compound D) a spirocyclic compound E) a racemic mixture 93) D SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 94) Draw (Z)-1, 3-hexadiene in its s-trans conformation. 94) 95) What is the product of the following Diels-Alder reaction? 95) 31

32 96) What diene and what dieneophile could be used to prepare the following? 96) 97) How could the following compound be synthesized using a Diels-Alder reaction? 97) 98) Cyclopentadiene can react with itself in a Diels-Alder reaction. Draw the endo and exo products. 98) 32

33 99) Provide the structure of the major organic product in the following reaction. 99) (plus enantiomer) 100) Provide the structure of the major organic product in the following reaction. 100) (plus enantiomer) 101) Provide the structure of the major organic product in the following reaction. 101) 33

34 102) Provide the structure of the major organic product in the following reaction. 102) 103) Provide the structure of the major organic product in the following reaction. 103) 104) Provide the structure of the major organic product in the following reaction. 104) 34

35 105) What diene and dienophile would react to give the product below? 105) 106) What diene and dienophile would react to give the product below? 106) 107) What diene and dienophile would react to give the product below? 107) 35

36 108) What diene and dienophile would react to give the product below? 108) 109) Why does the (E,E)-isomer of 2, 4-hexadiene react much more rapidly with dienophiles than does the (Z,Z)-isomer? 109) The s-cis conformation, which is required for participation in a Diels-Alder reaction, is hindered by a severe CH 3 /CH 3 steric interaction in the (Z,Z)-isomer. 110) What diene and dienophile should be used to synthesize the compound below? 110) 36

37 111) What diene and dienophile should be used to synthesize the compound below? 111) 112) What diene and dienophile should be used to synthesize the compound below and its enantiomer? 112) 113) What diene and dienophile should be used to synthesize the compound below and its enantiomer? 113) 37

38 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 114) Which of the following is an isolated diene? 114) A) I B) II C) III D) IV E) V D SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 115) What is the hybridization of the carbons labeled A, B, and C? 115) sp2, sp3, sp 38