aroma 1 all - abrigas/w_aroma_1_all.pdfMULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) ... completes each statement or answers the question. 61) ...

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  • Exam

    Name___________________________________

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

    1) Which of the following is an incorrect description of benzene?

    A) The molecule is planar.

    B) The molecule is aromatic.

    C) The molecule can be drawn as a resonance hybrid of two Kekule structures.

    D) The CCC bond angles are all equal to 120.

    E) The molecule is a 6-membered ring which contains alternating single and double

    carbon-carbon bonds.

    1)

    ESSAY. Write your answer in the space provided or on a separate sheet of paper.

    2) Why does benzene undergo a substitution reaction with Br2 while cyclohexene undergoes an addition reaction.

    3) 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?

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

    4) Cyclic hydrocarbons which can be represented as structures containing alternating single

    and double bonds are called __________.

    4)

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

    5) In the molecular orbital representation of benzene, how many molecular orbitals are present?

    A) 8 B) 1 C) 2 D) 6 E) 4

    5)

    6) How many distinct nodal planes which are perpendicular to the molecular plane are present in the

    4* orbital of benzene?

    A) 0 B) 1 C) 2 D) 4 E) 5

    6)

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

    7) 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.

    7)

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

    8) How many pairs of degenerate molecular orbitals are found in benzene?

    A) 3 B) 5 C) 2 D) 6 E) 4

    8)

    ESSAY. Write your answer in the space provided or on a separate sheet of paper.

    9) Show how the participating p orbitals interact to form the highest energy molecular orbital of benzene.

    10) List the criteria which compounds must meet in order to be considered aromatic.

    11) Which is more stable, cyclobutadiene or 1,3-butadiene? Explain.

    1

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

    12) Aromatic molecules contain __________ electrons.

    A) 4n + 1 (with n an integer)

    B) unpaired

    C) 4n + 2 (with n an integer)

    D) 4n (with n an integer)

    E) no

    12)

    ESSAY. Write your answer in the space provided or on a separate sheet of paper.

    13) Is cyclooctatetraene a planar molecule? Explain.

    14) Is the all-cis form of [10]annulene aromatic? Explain.

    15) Is the [10]annulene shown below aromatic? Explain.

    16) Provide the major resonance structures of the ion which results when the most acidic hydrogen of

    cyclopentadiene is lost.

    17) Explain the relative acidities of cyclohexene (pKa of 46) and cyclopentadiene (pKa of 16).

    18) Why would the reaction below proceed at an extremely slow rate if at all?

    19) When cycloheptatriene is deprotonated, an anion with seven resonance forms of equal energy can be drawn.

    Given this fact, explain why cycloheptatriene is only slightly more acidic than propene.

    20) 3-Chlorocyclopropene is solvolyzed in methanol at a much higher rate than is chlorocyclopropane. Offer an

    explanation.

    21) Classify 1,3,5-heptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    22) Classify cyclopentadienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    23) Classify cyclopropenyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network

    24) Classify cycloheptatrienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    25) Classify naphthalene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    2

  • 26) Classify pyridine as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    27) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    28) Classify the compound below as aromatic antiaromatic, or nonaromatic. Assume planarity of the network.

    29) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    30) Classify cycloheptatriene as aromatic antiaromatic, or nonaromatic. Assume planarity of the network.

    31) Classify cyclopentadiene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.

    32) Which is more basic, pyridine or pyrrole? Explain.

    33) Why are researchers interested in the properties of large polynuclear aromatic hydrocrobons?

    34) Provide the structure of the major organic product which results when phenanthrene is treated with Br2 in

    carbon tetrachloride.

    35) Provide an acceptable name for the compound below.

    3

  • 36) Provide an acceptable name for the compound below.

    37) Provide an acceptable name for the compound below.

    38) Provide an acceptable name for the compound below.

    39) Provide an acceptable name for the compound below.

    40) Provide the structure of m-nitrophenol.

    41) Provide the structure of anisole.

    42) Provide the structure of indole.

    43) Provide the structure of o-bromostyrene.

    44) Provide the structure of 2-bromo-4-chlorobenzoic acid.

    45) Provide the structure of 4-isopropylbenzaldehyde.

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

    46) Which of the following compounds has the lowest boiling point?

    A) 1,2,4-tirchlorobenzene

    B) p-dichlorobenzene

    C) 1,2,3-trichlorobenzene

    D) o-dichlorobenzene

    E) m-dichlorobenzene

    46)

    4

  • 47) Which of the following compound has the highest melting point?

    A) toluene

    B) p-dichlorobenzene

    C) o-dichlorobenzene

    D) benzene

    E) m-dichlorobenzene

    47)

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

    48) The IR spectrum of m-xylene contains stretches which are characteristic of most aromatic

    hydrocarbons. List the peaks (in cm-1) associated with the aromatic CC stretch and the

    aromatic CH stretch.

    48)

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

    49) In the proton NMR, in what region of the spectrum does one typically observe hydrogens bound to

    the aromatic ring?

    A) 1.0-1.5 ppm

    B) 2.0-3.0 ppm

    C) 4.5-5.5 ppm

    D) 7.0-8.0 ppm

    E) 9.0-10.0 ppm

    49)

    50) In the carbon NMR, in what region of the spectrum does one typically observe carbons which are

    part of the aromatic ring?

    A) -10-0 ppm

    B) 40-60 ppm

    C) 80-100 ppm

    D) 120-150 ppm

    E) 200-220 ppm

    50)

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

    51) How might one distinguish the isomers of trimethylbenzene by noise-decoupled 13C

    NMR?

    51)

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

    52) Which of the following compounds has the most signals in the noise-decoupled 13C NMR

    spectrum?

    A) o-dibromobenzene

    B) m-dibromobenzene

    C) 1,2,3,4-tetrabromobenzene

    D) 1,3,5-tribromobenzene

    E) p-dibromobenzene

    52)

    53) In the mass spectrum of isobutylbenzene, the base peak occurs at m/z:

    A) 119 B) 105 C) 133 D) 91 E) 134

    53)

    ESSAY. Write your answer in the space provided or on a separate sheet of paper.

    54) Describe the benzenoid band which appears in the UV-visible spectrum of most aromatic hydrocarbons.

    5

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

    55) In the UV-visible spectra of the following compounds, in which does lambda max appear at the

    highest wavelength?

    A) isopropylbenzene

    B) 1-phenylpropene

    C) 3-phenylpropene

    D) benzene

    E) n-octylbenzene

    55)

    56) How many distinct trichlorobenzene isomers are possible?

    A) 3 B) 2 C) 4 D) 6 E) 5

    56)

    57) Which of the following is another accepted name for methyl phenyl ketone?

    A) cresol

    B) anisole

    C) acetophenone

    D) cresone

    E) benzophenone

    57)

    58) Which of the following undergoes SN2 reaction with sodium methoxide most rapidly?

    A) PhCH2CH2Br

    B) PhCH2Br

    C) PhCH2CH2CH2Br

    D) Ph3CBr

    E) PhBr

    58)

    59) Which of the following undergoes solvolysis in methanol most rapidly?

    A) Ph3CBr

    B) PhCH2CH2Br

    C) PhCH2CH2CH2Br

    D) PhCH2Br

    E) PhBr

    59)

    60) Which of the following is not a fused-ring heterocycle?

    A) pyrimidine

    B) benzofuran

    C) indole

    D) purine

    E) quinoline

    60)

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

    61) When cyclohexene is treated with KMnO4, H2O, the syn-1,2-diol is produced. What

    reaction occurs when benzene is similarly treated?

    61)

    6

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

    62) Which of the following is another name for cyclobutadiene?

    A) [6]annulene

    B) antibenzene

    C) Dewar benzene

    D) [4]annulene

    E) [2]annulene

    62)

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

    63) Classify pyrrole as aromatic, antiaromatic, or nonaromatic. Assume planarity of the

    network.

    63)

    ESSAY. Write your answer in the space provided or on a separate sheet of paper.

    64) Provide the structure of pyrimidine.

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

    65) __________ is similar to furan, with a sulfur atom in place of the oxygen. 65)

    ESSAY. Write your answer in the space provided or on a separate sheet of paper.

    66) Provide the structure of anthracene.

    67) Provide an acceptable name for PhSO3H.

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

    68) Which of the following is also an acceptable name for 3-nitrophenol?

    A) m-nitrophenol

    B) p-nitrophenol

    C) hydroquinone

    D) 3-cresol

    E) o-nitrophenol

    68)

    69) Which of the following is also an acceptable name for 1,3,5-trimethylbenzene?

    A) 1,3,5-xylene

    B) styrene

    C) cumene

    D) cymene

    E) mesitylene

    69)

    70) Which of the following is the same as the tropylium ion?

    A) cyclopropenyl anion

    B) cyclopentadienyl cation

    C) cyclopentadienyl anion

    D) cycloheptatrienyl anion

    E) cycloheptatrienyl cation

    70)

    7

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

    71) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume

    planarity of the network.

    71)

    72) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume

    planarity of the network.

    72)

    73) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume

    planarity of the network.

    73)

    74) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume

    planarity of the network.

    74)

    8

  • 75) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume

    planarity of the network.

    75)

    76) Provide an acceptable name for the compound below. 76)

    77) Provide the structure of m-xylene. 77)

    78) Provide the structure of o-toluic acid. 78)

    79) Provide the structure of 2,5-dichlorophenol. 79)

    80) Name two of the three common allotropes of carbon. 80)

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

    81) What is the bond order of the carbon-carbon bonds in benzene?

    A) 0.5 B) 2 C) 1 D) 3 E) 1.5

    81)

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

    82) Describe the occupied p molecular orbitals in the gound state of cyclobutadiene. 82)

    83) What compound results when cyclooctatetraene is treated with excess potassium metal? 83)

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

    84) Nitrogen's lone pair electrons occupy what type of orbital in pyridine?

    A) p B) s C) sp D) sp2 E) sp3

    84)

    9

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

    85) Provide the structure of o-chlorotoluene. 85)

    86) Provide the structure of tropylium bromide. 86)

    87) Provide the structure of p-aminobenzoic acid. 87)

    88) Provide the structure of sodium cyclopentadienide. 88)

    89) Provide the structure of 2,4,6-trichlorophenol. 89)

    90) Provide the structure of m-iodobenzoic acid. 90)

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

    91) What is the major difference between an antiaromatic and aromatic compound?

    A) Aromatic compounds cannot have a charged atom in the structure

    B) Antiaromatic compounds can assume a chair-like structure while aromatic compounds are

    nearly flat

    C) Antiaromatic compounds have at least one sp3 hybridized atom in the ring

    D) Only aromatic compounds follow Huckle's rule.

    E) The structure must be cyclic for aromatic but not antiaromatic compounds?

    91)

    10

  • 92) Which of the following structures is aromatic?

    A)

    B)

    C)

    D)

    E)

    92)

    11

  • 93) Which of the following structures, if flat, would be classified as antiaromatic?

    A)

    B)

    C)

    D)

    E)

    93)

    12

  • 94) Which of the labeled H atoms (1 -5) in the following molecule would be predicted to be the most

    acidic?

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

    94)

    95) Rank the following in order of increasing pKa (from lowest to highest pKa)

    A) 1 < 2 < 3 B) 2 < 1 < 3 C) 3 < 2 < 1 D) 2 < 3 < 1 E) 3 < 1 < 2

    95)

    13

  • Answer KeyTestname: AROMA_1_ALL

    1) E

    2) Addition of Br2 to benzene is highly unfavorable because it would result in a nonaromatic product.

    3) This suggests that the type of bonding in benzene lends special stability to the molecule.

    4) annulenes

    5) D

    6) C

    7)

    8) C

    9) All adjacent interactions are antibonding.

    10) 1. The structure must be cyclic.

    2. Each atom in the ring must have an unhybridized p orbital.

    3. The structure must be planar or nearly planar so that overlap of these p orbitals is effective.

    4. The network must contain 4n + 2 electrons (where n is a whole number), so that delocalization of the electrons

    results in a lowering of the molecule's electronic energy.

    11) 1,3-Butadiene is more stable. Cyclobutadiene is antiaromatic since it contains 4 (i.e., 4n) electrons. Antiaromatic

    systems are less stable than their open-chain counterparts.

    12) C

    13) No. In addition to increasing other forms of strain, a planar conformation would make this molecule antiaromatic.

    14) No. Planarity, which is required for aromaticity, is precluded due to excessive angle strain.

    15) No. The ring cannot achieve a planar conformation since such a conformation would result in severe and unfavorable

    steric interactions between the two H's oriented inside the ring.

    16)

    17) The conjugate base of cyclopentadiene is aromatic.

    18) The carbocation intermediate involved in this reaction is antiaromatic. Based on Hammond's Postulate, one can

    surmise that the activation energy required to produce this intermediate would be very high.

    19) Each resonance form of the cyclopehtatrienyl anion is antiaromatic.

    20) Cyclopropenyl cation, the carbocationic intermediate in the case of 3-chlorocycloprene, is aromatic and via

    Hammond's Postulate we can say that the activation energy required to form it is lower.

    21) nonaromatic

    14

  • Answer KeyTestname: AROMA_1_ALL

    22) antiaromatic

    23) aromatic

    24) aromatic

    25) aromatic

    26) aromatic

    27) aromatic

    28) aromatic

    29) aromatic

    30) nonaromatic

    31) nonaromatic

    32) Pyrrole is a much weaker base than pyridine. When pyrrole is protonated, the system's aromaticity is destroyed.

    33) These compounds are formed to some extent in nearly all combustion reactions of organic compounds and are known

    to be potent carcinogens.

    34)

    35) aniline or aminobenzene or benzeneamine

    36) para-dichlorobenzene or 1,4-dichlorobenzene

    37) 2,4-dinitrotoluene

    38) imidazole

    39) ortho-xylene or 1,2-dimethylbenzene

    40)

    41)

    42)

    43)

    15

  • Answer KeyTestname: AROMA_1_ALL

    44)

    45)

    46) B

    47) B

    48) CC: around 1600 cm-1

    CH: just above 3000 cm-1 (usually around 3030 cm-1)

    49) D

    50) D

    51) 1,3,5-trimethylbenzene: 3 signals

    1,2,4-trimethylbenzene: 9 signals

    1,2,3-trimethylbenzene: 6 signals

    52) B

    53) D

    54) Band centered at 254 nm; 3-6 small, sharp peaks; weak molar absorptivity.

    55) B

    56) A

    57) C

    58) B

    59) A

    60) A

    61) No reaction takes place.

    62) D

    63) aromatic

    64)

    65) Thiophene

    66)

    67) benzenesulfonic acid

    68) A

    69) E

    70) E

    71) antiaromatic

    72) aromatic

    73) nonaromatic

    74) nonaromatic

    75) aromatic

    16

  • Answer KeyTestname: AROMA_1_ALL

    76) 1,3,5-trinitrobenzene

    77)

    78)

    79)

    80) diamond; graphite; fullerenes (like buckminsterfullerene)

    81) E

    82) Two electrons are paired in a bonding p molecular orbital, while the other two electrons are unpaired and singly

    occupy two nonbonding p molecular orbitals.

    83) dipotassium cyclooctatetraene dianion

    84) D

    85)

    86)

    17

  • Answer KeyTestname: AROMA_1_ALL

    87)

    88)

    89)

    90)

    91) D

    92) E

    93) E

    94) D

    95) B

    18

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