Deck 13: Structure Determination

Question 1

Instructions: Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.


-C-C, C-O, C-N, and C-X single-bond vibrations.

A)4000 to 2500 cm^-1
B)2500 to 2000 cm^-1
C)2000 to 1500 cm^-1
D)below 1500 cm^-1

Answer 1

below 1500 cm^-1

Question 2

The amount of energy in electromagnetic radiation is related to the frequency and wavelength of the radiation. High energy radiation, like gamma rays, is of:

A) low frequency and short wavelength
B) low frequency and long wavelength
C) high frequency and short wavelength
D) high frequency and long wavelength

Answer 2

high frequency and short wavelength

Question 3

Assume you are carrying out the conversion of 1-bromobutane to butan-1-ol. How could you use IR spectroscopy to determine when the reaction is complete?

Answer 3

The infrared spectrum of the starting bromide contains only alkyl C-H absorptions which appear in the 2850-2960 cm^-sup>1 region. As the reaction progresses, a broad absorption at 3400-3640 cm^-1, due to the O-H stretch, should develop. When the relative intensity of this band no longer increases, the reaction is complete.

Question 4

Instructions: Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.


-N-H, C-H, and O-H stretching and bending motions.

A)4000 to 2500 cm^-1
B)2500 to 2000 cm^-1
C)2000 to 1500 cm^-1
D)below 1500 cm^-1

Question 5

Which of the following regions in the electromagnetic spectrum corresponds to the radiation with the highest energy?

A) radio waves
B) ultraviolet
C) infrared
D) visible

Question 6

Instructions: Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.


-triple bond stretching vibrations.

A)4000 to 2500 cm^-1
B)2500 to 2000 cm^-1
C)2000 to 1500 cm^-1
D)below 1500 cm^-1

Question 7

Instructions: Refer to the mass spectrum of 2-methylbutane shown below to answer the following question(s). (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. What peak represents the base peak?

Question 8

Cyclohexene and hex-2-yne both have the molecular formula, C₆H₁₀.
a)How would you use infrared spectroscopy to distinguish between the two compounds?
b)How could the mass spectrum be used to distinguish between the two compounds?

Question 9

Below is the mass spectrum of an unknown hydrocarbon. In addition, this hydrocarbon shows characteristic absorption at 2100 cm ^{- 1} in its IR spectrum. Give the structure of this unknown. (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

Question 10

Instructions: Select the most reasonable formula for the compounds with the following mass spectral data.

-Refer to instructions. M⁺ at m/z = 216

A) C₆H₁₃OCl
B) C₄H₈Br₂
C) C₁₀H₁₆
D) C₉H₁₂O

Question 11

Instructions: Match each of the following groups of bond-types to the region of the infrared spectrum in which their absorptions occur.


-C=O, C=N, and C=C bond absorptions.

A)4000 to 2500 cm^-1
B)2500 to 2000 cm^-1
C)2000 to 1500 cm^-1
D)below 1500 cm^-1

Question 12

Examining the infrared spectrum of a compound allows us to:

A) determine the types of functional groups present in the compound
B) determine the carbon-hydrogen framework of the compound
C) determine the molecular weight of the compound
D) determine the nature of the conjugated pi electron system in the compound

Question 13

What are the units for electromagnetic radiation used in infrared spectroscopy?

A) cm
B) cm^-1
C) J.mol^-1
D) none, wavenumber is a dimensionless quantity

Question 14

Which of the following does not involve the interaction of molecules with electromagnetic energy?

A) mass spectrometry
B) infrared spectroscopy
C) ultraviolet spectroscopy
D) nuclear magnetic resonance spectroscopy

Question 15

Which of the following statements best describes the base peak in a mass spectrum?

A) The peak from the most stable radical.
B) The peak from the species that has the isotope with the highest atomic number.
C) The peak of highest intensity.
D) The peak from the molecule minus an electron.
E) The M +1 peak

Question 16

Which of the following bonds undergoes stretching at the highest frequency?

A) C=O
B) C-O
C) C=C
D) C-C

Question 17

The amount of energy in infrared light corresponds to:

A) the amount of energy needed to promote one electron from a bonding to an antibonding molecular orbital
B) the amount of energy needed to fragment a molecule
C) the amount of energy needed to strip a molecule of one electron to generate a cation radical
D) the amount of energy needed to increase certain molecular motions, such as bond vibrations, in organic molecules

Question 18

Instructions: Refer to the mass spectrum of 2-methylbutane shown below to answer the following question(s). (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. What peak represents M⁺?

Question 19

Consider the compound below:
a)At what approximate positions might the compound show IR absorptions?
b)How would this spectrum differ from that of cyclohexanol?

Question 20

At what approximate positions might the compound below show IR absorptions?

Question 21

Which of the following compounds would show the longest wavelength $\lambda$ _max in its UV spectrum?

A)
B)
C)
D)

Question 22

Which of the following compounds gives an infrared spectrum with peaks at 3000-3500 cm^-1 and ~1750 cm^-1?

A)
B)
C)
D)

Question 23

Circle any of the following compounds that would be a candidate to produce a UV absorption spectrum.

Question 24

Which type of spectroscopy (IR, UV, or MS) will best distinguish between the pair of compounds below? Give a brief reason.

Question 25

What is the vertical axis of a mass spectrum?

A) mass
B) energy
C) abundance
D) field strength

Question 26

When an organic molecule is irradiated with ultraviolet radiation, the energy absorbed by the molecule corresponds to:

A) the amount necessary to increase molecular motions in functional groups
B) the amount necessary to excite electrons from one molecular orbital to another
C) the amount necessary to "flip" the spin of atomic nuclei
D) the amount necessary to strip a molecule of one electron to generate a radical cation

Question 27

Which of the following bonds undergoes stretching at the highest frequency?

A) O-H
B) C-H
C) C=O
D) C-C

Question 28

Which of the following compounds gives an infrared spectrum with peaks at 3300 cm=^-=¹ (strong, broad peak) and 1640 cm=^-=¹ (sharp, weak peak)?

A)
B)
C)
D)

Question 29

When 2-bromopropane reacts with ethoxide ion, two products are formed; one is the product of S_N2 substitution and the other is the product of E2 elimination. Write the structures of both products, and tell how they could be distinguished using IR spectroscopy.

Question 30

Instructions: The following questions pertain to the charting of NMR spectra. MATCH a term to each description below. Place the letter of the term in the blank to the left of the description.


-Refer to instructions. __________ The exact place on the chart at which a nucleus absorbs is called its __________.

A)TMS
B)high-field or upfield side
C)MHz
D)delta $\delta$
E)low-field or downfield side
F)chemical shift
G)specific absorption

Question 31

Which of the following compounds gives an infrared spectrum with peaks at 3300 cm^-1 (sharp peak) and 2150 cm^-1 (sharp peak)?

A)
B)
C)
D)

Question 32

A 3.42 *10^-5 M solution of dibenzalacetone in ethanol produced an absorbance of 0.753 in a 1.00 cm cell. Based on this data, what is $\varepsilon$ for this compound?

A) 2.57 * 10⁵
B) 2.20 * 10⁴
C) 4.54 *10^-5
D) 2.92 * 10⁴

Question 33

Which of the following compounds gives an infrared spectrum with a peak at ~1750 cm^-1, but no significant peaks at 3000-3500 cm^-1 or 1050-1250 cm^-1?

A)
B)
C)
D)

Question 34

Which of the following compounds gives an infrared spectrum with a peak at strong 1730 cm^-1?

A)
B)
C)
D)

Question 35

Which of the following bonds gives rise to a strong absorbance near 1700 cm^-1 in the infrared spectrum?

A) C=O
B) C-O
C) C=C
D) C-C

Question 36

Nuclear magnetic resonance spectroscopy provides information about a molecule's:

A) conjugated pi electron system
B) size and formula.
C) carbon-hydrogen framework.
D) functional groups.

Question 37

Instructions: The following questions pertain to the charting of NMR spectra. MATCH a term to each description below. Place the letter of the term in the blank to the left of the description.


-Refer to instructions. __________ The calibration standard for ¹H and ¹³C NMR is:

A)TMS
B)high-field or upfield side
C)MHz
D)delta $\delta$
E)low-field or downfield side
F)chemical shift
G)specific absorption

Question 38

What is the horizontal axis of a mass spectrum?

A) mass
B) mass/energy
C) mass/charge
D) charge

Question 39

Which of the following compounds would have the longest $\lambda$ _max in the UV region of the electromagnetic spectrum?

A) A
B) B
C) C
D) All would have the same $\lambda$ _max.

Question 40

Instructions: The following questions pertain to the charting of NMR spectra. MATCH a term to each description below. Place the letter of the term in the blank to the left of the description.


-Refer to instructions. __________ When looking at an NMR chart the right-hand part of the chart is the __________.

A)TMS
B)high-field or upfield side
C)MHz
D)delta $\delta$
E)low-field or downfield side
F)chemical shift
G)specific absorption

Question 41

Instructions: The following questions pertain to the charting of NMR spectra. MATCH a term to each description below. Place the letter of the term in the blank to the left of the description.


-Refer to instructions. __________ The NMR charts are calibrated using an arbitrary scale that is divided into __________ units.

A)TMS
B)high-field or upfield side
C)MHz
D)delta $\delta$
E)low-field or downfield side
F)chemical shift
G)specific absorption

Question 42

Which feature in the ¹H NMR spectrum provides information about the relative numbers of hydrogen atoms of each type found in a compound?

A) number of signals
B) integration of signals
C) splitting of signals
D) chemical shift

Question 43

Instructions: For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 44

Instructions: For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 45

Which of the following compounds would produce the most downfield signal in a ¹³C NMR spectrum?

A) A
B) B
C) C
D) D

Question 46

Which of the following would produce only singlets in an ¹H NMR spectrum?

A) A
B) B
C) C
D) D
E) all of these produce only singlets

Question 47

Instructions: Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).
Refer to instructions. What is the ratio of peak areas upon integration of the spectrum for A, B, and C respectively?

A) 3:1:3:3
B) 1:1:6.
C) 1 : 1: 6
D) 3:1:6

Question 48

A compound with the molecular formula C₆H₄ClBr produces only two doublets in the ¹H NMR spectrum.
a)Propose a structure for this compound.
b)How many signals would be present in the ¹³CNMR for this structure?

Question 49

Instructions: For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 50

Instructions: For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 51

Instructions: Predict the splitting patterns you would expect for each proton in the molecules below:
Predict:

Question 52

Instructions: Answer the following question(s) for the compound whose ¹H NMR spectra is shown below.
C₄H₈O (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)
Refer to instructions. Propose a structure for this compound.

Question 53

Treatment of tert-butyl alcohol with hydrogen chloride yields a mixture of tert-butyl chloride and 2-methylpropene. a)After chromatographic separation, how would you use ¹H NMR to help you decide which was which?
b)How would the ¹³C NMR for the two compounds differ?

Question 54

Instructions: Answer the following question(s) for the compound whose ¹H NMR spectra is shown below.
C₄H₈O (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

-Refer to instructions. Describe each signal in terms of its integration, splitting and chemical shift.

Question 55

Instructions: Predict the splitting patterns you would expect for each proton in the molecules below:
Predict:

Question 56

A compound with the molecular formula C₅H₁₂O produces only two singlets in the ¹H NMR spectrum.
a)Propose a structure for this compound.
b)How many signals would be present in the ¹³C NMR for this structure?

Question 57

Instructions: For each of the compounds below tell how many signals you would expect the molecule to have in its normal, broadband decoupled ¹³C NMR spectra.
Number of signals:

Question 58

Which structure of molecular formula C₄H₈Cl₂ fits the ¹H NMR and ¹³C NMR spectra shown below? (Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/)

A)
B)
C)
D)

Question 59

Instructions: The following questions pertain to the charting of NMR spectra. MATCH a term to each description below. Place the letter of the term in the blank to the left of the description.


-Refer to instructions. __________ The NMR charts are calibrated using an arbitrary scale that is divided into __________ units.

A)TMS
B)high-field or upfield side
C)MHz
D)delta $\delta$
E)low-field or downfield side
F)chemical shift
G)specific absorption

Question 60

Instructions: Refer to the structure of 3-methylbutan-2-one below to answer the following question(s).
Refer to instructions. What is the splitting pattern for the hydrogens in 3-methylbutan-2-one labeled A, B, and C, respectively?

A) singlet, singlet, singlet
B) singlet, septet, quartet
C) singlet, septet, doublet
D) singlet, septet, doublet, doublet

Question 61

Which of the following combinations of peaks appears in the ¹H NMR spectrum of 2-methylpropane?

A) two singlets
B) a singlet and a nonet
C) a singlet and a decet
D) a doublet and a decet

Question 62

Which feature in the ¹H NMR spectrum provides information about the electronic environment of the protons in a compound?

A) number of signals
B) integration of signals
C) splitting of signals
D) chemical shift

Question 63

Which of the following compounds gives a ¹H NMR spectrum consisting of only two singlets?

A) CH₃OCH₂CH₂OCH₂CH₃
B) CH₃OCH₂CH₂CH₂CH₂OH
C) CH₃OC(CH₃)₂OCH₃
D) CH₃OCH₂CH(CH₃)OCH₃

Question 64

Which of the following combinations of peaks appears in the ¹H NMR spectrum of diethyl ether, CH₃CH₂OCH₂CH₃?

A) a triplet and a doublet
B) a quartet and a sextet
C) two singlets
D) a triplet and a quartet

Question 65

Which feature in the ¹H NMR spectrum provides information about the number of neighboring protons of each proton in the compound?

A) number of signals
B) integration of signals
C) splitting of signals
D) chemical shift