orgo 2 chp 12

106) 2-Methylhexane shows an intense peak in the mass spectrum at m/z = 43. Propose a likely structure for this fragment.

Answer: (CH3)2CH+ Diff: 1 Section: 12.15

1) Which bond in the structure below would give rise to the highest absorption frequency in an IR spectrum? A) sp2 C-H B) sp3 C-H C) C-D D) C=C 3) Which sequence correctly ranks the regions of the electromagnetic spectrum in order of increasing energy? 1) infrared 2) ultraviolet 3) radio wave A) 3 < 1 < 2 B) 3 < 2 < 1 C) 2 < 1 < 3 D) 1 < 3 < 2 Answer: A Diff: 1 Section: 12.2 4) Absorption of what type of electromagnetic radiation results in ionization? A) X-rays B) radio waves C) microwaves D) ultraviolet light E) infrared light Answer: A Diff: 2 Section: 12.2 5) Absorption of what type of electromagnetic radiation results in electronic transitions? A) X-rays B) radio waves C) microwaves D) ultraviolet light E) infrared light Answer: D Diff: 2 Section: 12.2 6) Absorption of what type of electromagnetic radiation results in transitions among allowed rotational motions? A) X-rays B) radio waves C) microwaves D) ultraviolet light E) infrared light Answer: C Diff: 2 Section: 12.2 7) Absorption of what type of electromagnetic radiation results in transitions among allowed vibrational motions? A) X-rays B) radio waves C) microwaves D) ultraviolet light E) infrared light Answer: E Diff: 2 Section: 12.2 8) Absorption of what type of electromagnetic radiation results in transitions among allowed nuclear magnetic spin states? A) X-rays B) radio waves C) microwaves D) ultraviolet light E) infrared light Answer: B Diff: 2 Section: 12.2 9) Which of the following equations is equal to frequency? A) hλ B) c/λ C) hc/λ D) 1/λ Answer: B Diff: 2 Section: 12.2 10) The energy of a photon is __________ proportional to its wavelength. Answer: inversely Diff: 1 Section: 12.2 11) The energy of a photon is __________ proportional to its frequency. Answer: directly Diff: 1 Section: 12.2 12) In what units are frequency values typically given? Answer: Hertz or cycles/sec or sec-1 Diff: 1 Section: 12.2 13) Provide an equation which relates the energy of a photon to its wavelength. Answer: E = (hc)/λ Diff: 1 Section: 12.2 14) Arrange the following regions of the electromagnetic spectrum in order of increasing energy: microwave, UV, visible, and IR. Answer: microwave < IR < visible < UV Diff: 1 Section: 12.2 15) Arrange the following regions of the electromagnetic spectrum in order of increasing wavelength: X ray, radio, UV, and IR. Answer: X ray < UV < IR < radio Diff: 1 Section: 12.2 16) Which has the higher speed in a vacuum, ultraviolet or infrared light? Answer: They have the same speed. Diff: 2 Section: 12.2 17) The wavelength and frequency of a given wave of electromagnetic radiation are __________ proportional. Answer: inversely Diff: 2 Section: 12.2 18) Which region of the electromagnetic spectrum, IR or UV, contains photons of the higher energy? Answer: UV Diff: 2 Section: 12.2 19) Which region of the electromagnetic spectrum, radio or visible, is characterized by waves of shorter wavelength? Answer: visible Diff: 2 Section: 12.2 20) Which region of the electromagnetic spectrum, IR or X-ray, is characterized by waves of lower frequency? Answer: IR Diff: 2 Section: 12.2 21) An infrared wavelength of 4.48μm is equivalent to a wavenumber of __________ cm-1. Answer: 2230 Diff: 2 Section: 12.3 22) An infrared wavelength of 5.81μm is equivalent to a wavenumber of __________ cm-1. Answer: 1720 Diff: 2 Section: 12.3 23) At approximately what wavenumber does one expect to find the carbon-carbon triple bond stretch in the IR spectrum of an alkyne? Answer: 2100 - 2200 cm-1 Diff: 2 Section: 12.3 24) What wavenumber corresponds to the wavelength of 4 μm? Answer: 2500 cm-1 Diff: 2 Section: 12.3 25) What wavelength in mm is equivalent to a wavenumber of 1750 cm-1? Answer: 5.71 mm Diff: 2 Section: 12.3 26) The frequency of the stretching vibration of a bond in IR spectroscopy depends on what two quantities? A) the stiffness of the bond and the electronegativity of the atoms B) the electronegativity of the atoms and the nuclear charges of the atoms C) the masses of the atoms and the stiffness of the bond D) the nuclear charges of the atoms and the atomic radii E) the electronegativity of the atoms and the masses of the atoms Answer: C Diff: 2 Section: 12.4 27) In IR spectroscopy, the CO bond has a __________ frequency than the CN bond because __________. A) higher, an O atom has more mass than an N atom B) lower, an O atom has more mass than an N atom C) higher, an O atom has more electronegativity than an N atom D) lower, an O atom has more electronegativity than an N atom E) higher, an O atom has an even number of neutrons Answer: B Diff: 2 Section: 12.4 28) Which of the following stretches tends to be the least intense? A) O-H (alcohol) B) O-H (carboxylic acid) C) C-H D) C=O E) C=C Answer: E Diff: 2 Section: 12.4 29) A nonlinear molecule with n atoms generally has __________ fundamental vibrational modes. A) 2n B) 2n - 2 C) 3n D) 3n - 3 E) 3n - 6 Answer: E Diff: 3 Section: 12.4 30) The region of the IR spectrum which contains the most complex vibrations (600-1400 cm-1) is called the __________ region of the spectrum. Answer: fingerprint Diff: 2 Section: 12.4 31) How might pentane and heptane be distinguished by IR spectroscopy? Answer: Very similar spectra; differ most in the fingerprint region; use a spectral library Diff: 2 Section: 12.4 32) Which has a lower characteristic stretching frequency, the C-H or C-D bond? Explain briefly. Answer: C-D; heavier atoms vibrate more slowly Diff: 3 Section: 12.4 33) Which has a lower characteristic stretching frequency, the C=O bond or the C-O bond? Explain briefly. Answer: Stronger bonds are generally stiffer, thus requiring more force to stretch or compress them. The C-O bond is the weaker of the two and hence has the lower stretching frequency. Diff: 3 Section: 12.4 34) Ethyne (HC≡CH) does not show IR absorption in the region 2000-2500 cm-1 because: A) C-H stretches occur at lower energies. B) C≡C stretches occur at about 1640 cm-1. C) there is no change in the dipole moment when the C≡C bond in ethyne stretches. D) there is a change in the dipole moment when the C≡C bond in ethyne stretches. Answer: C Diff: 2 Section: 12.5 35) In order for a vibration mode to be observable in the IR, the vibration must change the __________ of the molecule. Answer: dipole moment Diff: 2 Section: 12.5 36) In an IR spectrometer, the __________ uses prisms or diffraction gratings to allow only one frequency of light to enter the detector at a time. Answer: monochromator Diff: 2 Section: 12.6 37) One of the following functional groups, sometimes shows a single weak to medium IR adsorption peak in the 2100 to 2250 cm-1 range. Depending on the structure of the compound this peak is sometimes not present, making it easy to misinterpret the spectrum. Which functional group is it? A) Carbonyl B) Alkyne C) Alcohol D) Alkene E) Carboxylic acid Answer: B Diff: 1 Section: 12.7 38) Which compound would be expected to show intense IR absorption at 3300 cm-1? A) CH3C≡CCH3 B) butane C) but-1-ene D) CH3CH2C≡CH Answer: D Diff: 2 Section: 12.7 39) What effect does conjugation typically have on the frequency at which absorption by C=C occurs? A) Conjugation decreases the frequency at which absorption occurs. B) Conjugation increases the frequency at which absorption occurs. C) Conjugation does not affect the frequency at which absorption occurs. Answer: A Diff: 2 Section: 12.7 40) The IR spectrum of a sample contains absorptions at 3050, 2950, and 1620 cm-1. To what class of organic compound does this sample most likely belong? A) alkane B) alkene C) alkyne D) ester E) alcohol Answer: B Diff: 2 Section: 12.7 41) Which of the following most closely matches the CC stretching frequency? A) 3300 B) 3000 C) 2200 D) 1700 E) 1200 Answer: C Diff: 2 Section: 12.7 42) Which of the following has a C→H stretch that occurs at the highest stretching frequency? A) hexane B) hex-1-ene C) (E)-hex-2-ene D) hex-1-yne E) hex-2-yne Answer: D Diff: 2 Section: 12.7 43) Which of the following would not have a C-H stretch at about 3050 cm-1? A) 1-pentene B) 2-pentene C) 2-methyl-2-pentene D) 2,3-dimethyl-2-pentene E) 2,4-dimethyl-2-pentene Answer: D Diff: 2 Section: 12.7 44) Which of the following compounds would contain characteristic IR stretches at 3300 and 2200 cm-1? A) CH3CH2CHO B) CH3CH=CHCH2OH C) (CH3)2CHCN D) CH3CH2CH2C≡CH E) CH3C≡CCH2CH3 Answer: D Diff: 2 Section: 12.7 45) How could IR spectroscopy be used to distinguish between the following pair of compounds? CH2=CHCH2CH(CH3)2 and CH3CH2CH2CH(CH3)2 Answer: C=C stretch around 1640 cm-1; vinylic C=H stretch above 3000 cm-1 Diff: 1 Section: 12.7 46) Which of the following molecules would be expected to have its C=C stretching frequency at the highest wavenumber: benzene, 1,3-pentadiene, or 1-pentene? Answer: 1-pentene Diff: 2 Section: 12.7 47) How could IR spectroscopy be used to distinguish between the following pair of compounds? CH3CH2C≡CH and CH3C≡CCH3 Answer: Terminal alkyne stretch at 3300 cm-1, lower intensity C≡C absorption in internal alkyne Diff: 3 Section: 12.7 48) What m/z characterizes a strong peak in the mass spectrum of cyclopentanol? A) 86 B) 85 C) 84 D) 70 E) 68 Answer: E Diff: 2 Section: 12.8 49) Which compound has a strong and broad IR absorption centered at 3400 cm-1? A) 1-butanol B) octane C) diethyl ether D) 2-hexyne E) benzene Answer: A Diff: 2 Section: 12.8 50) Which compound has a single, weak IR absorption at 3300 cm-1? A) (CH3CH2)2NH B) CH3CH2CH2OH C) CH3CH2CN D) (CH3CH2)2O E) CH3CH=CHCH3 Answer: A Diff: 2 Section: 12.8 51) Which compound lacks a strong, characteristic IR absorption near 1700 cm-1? A) CH3CH2CO2H B) CH3CH2CHO C) (CH3CH2)2C=O D) (CH3CH2)2O E) H3CH2CO2CH3 Answer: D Diff: 2 Section: 12.8 52) Which compound would be expected to show intense IR absorption at 1715 cm-1? A) (CH3)2CHNH2 B) hex-1-yne C) 2-methylhexane D) (CH3)2CHCO2H Answer: D Diff: 1 Section: 12.9 53) Which compound would be expected to show intense IR absorption at 1746 cm-1? A) CH3CH2OCH2CH3 B) CH3CH2CN C) CH3CO2CH2CH3 D) CH3CH2SCH3 Answer: C Diff: 1 Section: 12.9 54) Which compound would be expected to show intense IR absorption at 2820, 2710 and 1705 cm-1? A) CH3COCH2CH3 B) PhCOCH3 C) PhCHO D) CH2=CHCOCH3 Answer: C Diff: 2 Section: 12.9 55) In addition to a carbonyl stretch, which of the following molecules exhibits two characteristic stretches at 2700 and 2800 cm-1? A) (CH3CH2)2CO B) CH3CH2CH2CHO C) CH3CH2CO2CH3 D) CH3CH2CH2CO2H E) CH3CH2CH2COCl Answer: B Diff: 2 Section: 12.9 56) Which of the following molecules would have the highest frequency carbonyl stretch? A) (CH3CH2)2CO B) CH3CH2CH2CHO C) CH3CH2CO2CH3 D) CH3CH2CH2CO2H E) CH3CH2CH2CONH2 Answer: C Diff: 2 Section: 12.9 57) Which of the following compounds has the lowest carbonyl stretching frequency? Answer: Diff: 2 Section: 12.9 58) Which compound would be expected to show intense IR absorption at 1680 cm-1? Answer: Compound C Diff: 3 Section: 12.9 59) How does the O-H stretch in the IR spectrum of a carboxylic acid differ from the O-H stretch of an alcohol? Answer: Because of the unusually strong hydrogen bonding in carboxylic acids, the broad O-H stretch is shifted to about 3000 cm-1 centered on top of the usual C-H absorption. This broad O-H absorption gives a characteristic overinflated shape to the peaks in the C-H region. Diff: 2 Section: 12.9 60) Which compound would be expected to show intense IR absorption at 2250 cm-1? A) CH3CH2CH2CO2H B) (CH3)2CHCH2OH C) (CH3)2CHCN D) CH3CH2CH2CONH2 Answer: C Diff: 2 Section: 12.10 61) Which of the following bonds, C-N, C=N, or C≡N, has an IR stretch around 1600 cm-1? Answer: C=N Diff: 2 Section: 12.10 62) Which IR band is typically more intense, the C≡C stretch or the C≡N stretch? Explain briefly. Answer: The C≡N stretch tends to be more intense because stretching resulting in a greater change in the bond dipole. Diff: 2 Section: 12.10 63) Which compound would be expected to show intense IR absorption at 3367, 3282 cm-1? A) but-1-ene B) PhCO2H C) CH3OCH2CH3 D) PhCH2NH2 Answer: D Diff: 1 Section: 12.11 64) Which compound would be expected to show intense IR absorption at 1640 cm-1? A) hex-1-ene B) 2-methylheptane C) CH3CH2CH2OH D) CH3CH2COCH3 Answer: A Diff: 1 Section: 12.11 65) Which of the following does not have a broad absorption with one or more spikes that is centered about 3300 cm-1 in the IR? A) (CH3CH2CH2)3N B) (CH3CH2CH2)2NH C) CH3CH2CH2NH2 D) (CH3)3CNH2 E) (CH2=CHCH2)2NH Answer: A Diff: 2 Section: 12.11 66) How could IR spectroscopy be used to distinguish between the following pair of compounds? (CH3)3N and CH3NHCH2CH3 Answer: N-H absorption near 3300 cm-1 Diff: 2 Section: 12.11 67) Rank the following bonds in order of increasing stretching frequency (cm-1) in IR spectroscopy: C-H, C≡C, C-O, C=O. Answer: C-O < C=O < C≡C < C-H Diff: 2 Section: 12.11 68) Rank the following bonds in order of increasing stretching frequency (cm-1) in IR spectroscopy: O-H, C≡N, C-N, and C=O. Answer: C-N < C=O < C≡N < O-H Diff: 2 Section: 12.11 69) Arrange the following IR bond stretches in order of increasing wavenumber: C-O, C≡C, O-H, and C=C. Answer: C-O < C=C < C≡C < O-H Diff: 2 Section: 12.11 70) Deduce a possible structure for the compound with the IR absorptions below. C3H3Br: 3300, 2900, 2100 cm-1 Answer: HC≡CCH2Br Diff: 2 Section: 12.11 71) Deduce a possible structure for the compound with the IR absorptions below. C3H5N: 2950, 2250 cm-1 Answer: CH3CH2CN Diff: 2 Section: 12.11 72) Deduce a possible structure for the compound with the IR absorptions below. C6H10: 3040, 2980, 1660 cm-1 Answer: cyclohexene Diff: 2 Section: 12.11 73) Deduce a possible structure for the compound with the IR absorptions below. C5H8O: 2950, 1750 cm-1 Answer: cyclopentanone Diff: 3 Section: 12.11 74) Deduce a possible structure for the compound with the IR absorptions below. C4H8O: 2950, 2820, 2715, 1715 cm-1 Answer: CH3CH2CH2CHO Diff: 3 Section: 12.11 75) Which of the following structures is consistent with the IR spectra shown below? A) B) C) D) E) Answer: A Diff: 1 Section: 12.12 76) Which compound would be expected to show intense IR absorption at 3363, 3185, 1660 cm-1? A) CH3CH2CH2OH B) (CH3)2CHNH2 C) CH3CH2CONH2 D) but-1-ene Answer: C Diff: 2 Section: 12.12 77) What two functional groups are represented in the following IR spectrum? Answer: aromatic ring and nitrile Diff: 2 Section: 12.12 78) Which of the following structures is consistent with the IR spectra shown below? A) B) C) D) E) Answer: E Diff: 3 Section: 12.12 79) Sodium borohydride can be used to reduce cyclohexanone to cyclohexanol. How could one use IR to determine if all starting material had been consumed? Answer: Presence of C=O stretch would indicate incomplete reaction. Diff: 2 Section: 12.12 80) 3-Pentanol can be oxidized to 3-pentanone using sodium dichromate. How can the completeness of conversion be gauged using IR spectroscopy? Answer: The absence of a strong, broad O-H peak (3200-3600 cm-1) would indicate complete reaction of the alcohol starting material. Diff: 2 Section: 12.12 81) How could IR spectroscopy be used to distinguish between the following pair of compounds? CH3OCH2CH3 and CH3CH2CH2OH Answer: O-H stretch at 3300 cm-1 Diff: 1 Section: 12.12 82) How could IR spectroscopy be used to distinguish between the following pair of compounds? HOCH2CH2CHO and CH3CH2CO2H Answer: A carboxylic acid will have a very broad O-H absorption near 3000 cm-1; an aldehyde has characteristic C-H stretches at 2820 and 2720 cm-1. Diff: 2 Section: 12.12 83) How could IR spectroscopy be used to distinguish between the following pair of compounds? CH3COCH=CHCH2CH3 and CH3COCH2CH2CH=CH2 Answer: C=O absorption in conjugated carbonyl appears at lower wavenumber Diff: 3 Section: 12.12 84) When a high energy electron impacts molecule M in the ionization chamber, what type of species is initially produced? A) cation B) anion C) radical D) radical cation E) radical anion Answer: D Diff: 2 Section: 12.13 85) In a mass spectrum, the peak of greatest abundance is referred to as the __________. Answer: base peak Diff: 1 Section: 12.13 86) Describe the fate of a molecule from introduction to detection in a mass spectrometer. Answer: Upon introduction, sample molecules are ionized by an electron beam passing through a vacuum chamber. The resulting radical cation and fragment cations are accelerated into the flight tube of the magnet by a negatively charged plate. In the flight tube, the path of the ions is bent by the existing magnetic field. For a given magnetic field strength, only one m/z will be bent in such a way that its path matches the curvature of the tube and reaches the detector. The entire m/z range is scanned by varying the strength of the magnetic field. Diff: 2 Section: 12.13 87) Which compound would show a larger than usual M+2 peak in the mass spectrum? A) CH3CH2SCH3 B) (CH3)2CHNH2 C) CH3CH2CO2H D) CH3(CH2)2CH3 Answer: A Diff: 1 Section: 12.14 88) An __________ molecular ion peak usually indicates the presence of an odd number of nitrogen atoms in the molecule. A) even B) odd C) intense D) absent Answer: B Diff: 1 Section: 12.14 89) The presence of which element is indicated by a peak at m/z 127 and a characteristic 127-unit gap in the mass spectrum? A) Br B) Cl C) I D) N E) S Answer: C Diff: 1 Section: 12.14 90) The two most abundant isotopes of boron are 10B and 11B, with 11B being about 4 times more abundant. In the mass spectrum of trimethylborate [(CH3O)3B], __________. A) the peaks at m/z 103 and m/z 104 have equivalent intensities B) the peak at m/z 103 has an intensity which is 4 times that of the m/z 104 peak C) the peak at m/z 103 has an intensity which is 1/4 the intensity of the peak at m/z 104 D) none of the above Answer: C Diff: 2 Section: 12.14 91) Which of the following structures is consistent with the mass spectrum shown below? A) B) C) D) E) Answer: E Diff: 2 Section: 12.14 92) What are the predicted m/z values (masses )and relative heights of all the molecular ions of 1-bromoethane that would appear on a mass spectrum (excluding peaks produced by 13C and 2H)? A) M+ peak at m/z =108 and an M+1 peak at m/z =110 The M+1 peak is approximately 1/2 the height of the M+ peak. B) M+ peak at m/z = 79 and an M+1 peak at 81 The M+1 peak is approximately the same height as the M+ peak. C) M+ peak at m/z = 108 and an M+2 peak at m/z = 110 The M+2 peak is approximately the same height as the M+ peak. D) M+ peak at m/z = 108 and an M+2 peak at m/z = 110 M+2 peak is approximately 1/2 the height of the M+ peak. E) M+ peak at m/z = 79 and an M+1 peak at 81 The M+1 peak is approximately 1/2 the height of the M+ peak. Answer: C Diff: 2 Section: 12.14 93) The mass spectrum of which compound has M+ and M+2 peaks of approximately equal intensity? A) 3-bromopentane B) 3-pentanol C) pentane D) 3-chloropentane E) 3-iodopentane Answer: A Diff: 2 Section: 12.14 94) The mass spectrum of which compound has an M+2 peak that has intensity that is about 25% of its M+ peak? A) 3-bromopentane B) 3-pentanol C) pentane D) 3-chloropentane E) 3-iodopentane Answer: D Diff: 2 Section: 12.14 95) The mass spectrum of which compound has an M+2 peak that has intensity that is about 4% of its M+ peak? A) (CH3CH2)2S B) (CH3CH2)2O C) CH3CH2CH2Br D) CH3CH2CH2NH2 E) CH3CH2CH2Cl Answer: A Diff: 2 Section: 12.14 96) When a compound contains a sulfur atom, its mass spectrum contains a larger than usual __________ peak. A) M-2 B) M-1 C) M D) M+1 E) M+2 Answer: E Diff: 3 Section: 12.14 97) What spectroscopic technique can be used to determine the molecular formula of a compound? Answer: high resolution mass spectrometry Diff: 2 Section: 12.14 98) If the mass spectrum of chlorobenzene shows a peak with an m/z value of 114, having an abundance of 15%, calculate the m/z value and approximate abundance of the molecular ion peak. Answer: m/z = 112, approximate abundance = 45% Diff: 2 Section: 12.14 99) In a mass spectrum, what m/z value would correspond to the following fragment? Answer: 148/2 = 74 amu Diff: 2 Section: 12.14 100) The natural abundances of chlorine's two major isotopes are 35Cl (75.5%) and 37Cl (24.5%). If the mass spectrum of chlorobenzene contains a peak at m/z 114 with an abundance of 15.0%, calculate the % abundance of the peak at m/z 112. Answer: 46.2% Diff: 2 Section: 12.14 101) Describe the molecular ion region in the mass spectrum of CH3CH2Br. Answer: The natural abundance of the isotopes 79Br and 81Br are about the same; therefore, there will be peaks of equal intensity at m/z 108 and 110. Diff: 3 Section: 12.14 102) Which of the following fragment peaks would not be present in the mass spectrum of n-hexane? A) 87 B) 71 C) 57 D) 43 E) 29 Answer: A Diff: 1 Section: 12.15 103) The mass spectrum of alcohols often fail to exhibit detectable M peaks but instead show relatively large __________ peaks. A) M+1 B) M+2 C) M-16 D) M-17 E) M-18 Answer: E Diff: 2 Section: 12.15 104) At what m/z would the base peak of (E)-2-hexene occur? A) 84 B) 69 C) 55 D) 41 E) 28 Answer: C Diff: 2 Section: 12.15 105) What compound has a significant m/z 70 in its mass spectrum? A) 1-pentanol B) 2-butanol C) diethyl ether D) octane E) (E)-2-pentene Answer: A Diff: 2 Section: 12.15 PAGE \* MERGEFORMAT 1

Answer: A Diff: 2 Section: 12.2

2) Absorption __________ is the measurement of the amount of light absorbed by a compound as a function of the wavelength of light. Diff: 1 Section: 12.1

Answer: spectroscopy