Deck 10: Structure Determination: Mass Spectrometry,infrared Spectroscopy,and Ultraviolet Spectroscopy

Question 1

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

Answer 1

the amount of energy needed to increase certain molecular motions,such as bond vibrations,in organic molecules

Question 2

What are the masses of the charged fragments produced by the dehydration of the following compound?

Answer 2

This compound has the formula C₉H₂₀O and a mass of 144.Dehydration will result in the loss of H₂O producing a charged fragment at m/z = 126,18 mass units less than M⁺.

Question 3

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?

Answer 3

The peak at m/z = 43 is the base peak.

Question 4

Arrange the following in order of increasing energy.
A.3842 nm
B.2870 cm^-1
C.2.91 ´ 10¹⁶ Hz
D.1.99 ´ 10^-18 J

Question 5

What are the masses of the charged fragments produced by alpha cleavage of the following?

Question 6

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

Question 7

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?

Question 8

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 9

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

Question 10

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 11

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 12

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 13

Instructions: Select the most reasonable formula for the compounds with the following mass spectral data.
Refer to instructions.M⁺ at m/z = 101

A)C₅H₆Br
B)C₅H₁₂N₂
C)C₆H₁₅N
D)C₉H₁₂O

Question 14

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

Question 15

Loratidine is the active ingredient in the antihistamine Claritin.Mass spectral analysis of loratidine shows M⁺ at m/z = 382.Loratidine is known to contain nitrogen.What is the minimum number of nitrogens in loratidine?

Question 16

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 17

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 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.Propose structures for fragment ions at m/z = 57,43,and 29.

Question 19

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 20

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 21

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

Question 22

What is the horizontal axis of a mass spectrum?

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

Question 23

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

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

Question 24

What region of the IR spectrum would be the most useful in distinguishing between the following two compounds?

A)Above 2850 cm^-1
B)Between 2850 and 2000 cm^-1
C)Between 2000 and 1500 cm^-1
D)Below 1500 cm^-1

Question 25

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 26

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 27

Which of the following peaks is not prominent in the mass spectrum of 2-methylbutan-2-ol?

A)M⁺ - 15
B)M⁺ - 18
C)M⁺ - 21
D)M⁺ - 29

Question 28

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 e for this compound?

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

Question 29

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

A)
B)
C)
D)

Question 30

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

Question 31

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

A)O-H
B)C-H
C)C=O
D)CºC

Question 32

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 33

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 34

Which of the following compounds would have the longest l_max in the UV region of the electromagnetic spectrum?

A)A
B)B
C)C
D)All would have the same l_max.

Question 35

Which of the following compounds gives an infrared spectrum with no significant peaks at ~3300 cm^-1 or 1600-1680 cm^-1?

A)
B)
C)
D)

Question 36

What is the vertical axis of a mass spectrum?

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

Question 37

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 38

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 39

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 40

Match a structure from the list below to the following IR spectra.

Question 41

The source of absorbance of light at a wavelength of 6600 nm would be:

A)p ® p* electron transitions
B)bond stretching
C)in-plane bending
D)out-of-plane bending
E)b,c,d