Question 1

In IR spectroscopy, an absorption occurs any time

Accepted Answer

A)  a vibration is located in a magnetic field. 
B)  vibrating bonds are conjugated. 
C)  any vibrating bond interacts with a light wave vibrating with the same frequency. 
D)  a vibrating dipole moment interacts with a light wave vibrating with the same frequency. 
E)  the mass of one atom involved in the vibration is much less than the mass of the others. 
A)  a vibration is located in a magnetic field. 
B)  vibrating bonds are conjugated. 
C)  any vibrating bond interacts with a light wave vibrating with the same frequency. 
D)  a vibrating dipole moment interacts with a light wave vibrating with the same frequency. 
E)  the mass of one atom involved in the vibration is much less than the mass of the others. D

Question 2

What is the energy (in kJ mol-1) of infrared radiation that has a wavenumber of 1600 cm-1? (Planck's constant = 3.99 × 10-13 kJ mol-1 sec; the velocity of light = 3 × 1010 cm sec-1)

Accepted Answer

Even if you do not remember the formula, this sort of problem can be done by dimensional analysis:
 $$E = h c { v } = \left( 3.99 \times 10 ^ { - 13 } \mathrm {~kJ} \mathrm {~mol} ^ { - 1 } \mathrm { sec } \right) \left( 3 \times 10 ^ { 10 } \mathrm {~cm} \mathrm { sec } ^ { - 1 } \right) \left( 1600 \mathrm {~cm} ^ { - 1 } \right) = 19.1 \mathrm {~kJ} \mathrm {~mol} ^ { - 1 }$$

Question 3

A compound with an unknown structure is investigated by determining both its EI (electron ionization) and CI (chemical ionization) mass spectra. Why would you use both and what information is gleaned from each?

Accepted Answer

Molecular ions in electron ionization are very high energy and likely to undergo fragmentation. In many cases, the molecular ion is not visible in the spectrum or too weak to be diagnostic. Chemical ionization is a milder process, where a gas is ionized instead, leading to formation of positive ions with the unknown structure. This leads to an easily identifiable M+1 peak, allowing the user to deduce the molecular mass. Electron ionization gives complementary fragmentation information, which can be used to deduce other aspects of the structure.

Question 4

Which species shown would not be detected in the electron ionization (EI) mass spectrometry?

Accepted Answer

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

Question 5

The C=C stretching absorption in the IR spectrum occurs at about 1650 cm-1. The C-C stretching vibration occurs but is not observed. Which of these frequencies would be closest to the frequency of the C-C stretching vibration?

Accepted Answer

A)  3300 cm-1 
B)  815 cm-1 
C)  2330 cm-1 
D)  1165 cm-1 
E)  (1650 cm-1)/2F1F1F1S1F1F1F10c, where c is the speed of light. 
A)  3300 cm-1 
B)  815 cm-1 
C)  2330 cm-1 
D)  1165 cm-1 
E)  (1650 cm-1)/2F1F1F1S1F1F1F10c, where c is the speed of light.

Question 6

The -C≡N stretching frequency in the infrared spectrum occurs at about 2220 cm-1. The C-N stretching frequency should occur at about

Accepted Answer

A)  740 cm-1 
B)  1010 cm-1 
C)  1280 cm-1 
D)  1820 cm-1 
A)  740 cm-1 
B)  1010 cm-1 
C)  1280 cm-1 
D)  1820 cm-1

Question 7

Methane (CH4) is vaporized in a vacuum chamber and bombarded with an electron beam of high energy to give the mass spectrum below. (a) Identify each of the labeled m/z peaks. (b) Explain the presence of the small peak at m/z 17.

Accepted Answer

(a) Methane is bombarded by a beam of hi

Question 8

Select the two true statements.

Accepted Answer

A)  An organic compound with a dipole moment absorbs all wavelengths of IR radiation equally. 
B)  Wavelength is proportional to the energy of a light wave. 
C)  IR absorption is caused by the interaction of the electric field of light with a vibrating bond dipole. 
D)  A necessary but not sufficient condition for IR absorption is a match between the frequency of the vibrational mode and the frequency of light. 
E)  A sufficient condition for IR absorption is a match between the frequency of the vibrational mode and the frequency of light.f. 
Every IR absorption corresponds to the vibration of an individual bond. 
A)  An organic compound with a dipole moment absorbs all wavelengths of IR radiation equally. 
B)  Wavelength is proportional to the energy of a light wave. 
C)  IR absorption is caused by the interaction of the electric field of light with a vibrating bond dipole. 
D)  A necessary but not sufficient condition for IR absorption is a match between the frequency of the vibrational mode and the frequency of light. 
E)  A sufficient condition for IR absorption is a match between the frequency of the vibrational mode and the frequency of light.f. 
Every IR absorption corresponds to the vibration of an individual bond.

Question 9

Which compound has an absorption at 700 cm-1?

Accepted Answer

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

Question 10

Two students perform a hydrolysis reaction on cis-2-pentene. Two alcohols are isolated and one of the students argues that he can prove the structure of each using electron ionization mass spectrometry. Do you agree with his argument? Explain.

Accepted Answer

First, determine the products expected i

Question 11

Use the structure, including the labels on appropriate protons and bonds, to answer the questions. Please note: Protons are uppercase, bonds are lowercase.

Accepted Answer

a. f
b. 20

Question 12

Which molecular vibration does not have an absorption in the IR spectrum?

Accepted Answer

A)  O=C=O symmetrical stretch 
B)  O=C=O unsymmetrical stretch 
C)  the carbonyl stretch in acetone, CH3C(=O)CH3 
D)  the alkene stretch in CH2=C(CH3)2 
A)  O=C=O symmetrical stretch 
B)  O=C=O unsymmetrical stretch 
C)  the carbonyl stretch in acetone, CH3C(=O)CH3 
D)  the alkene stretch in CH2=C(CH3)2

Question 13

Outline a synthesis for the transformation. Describe how you could use IR spectroscopy or mass spectrometry to monitor the completion of the reaction.

Accepted Answer

@#IMG-DLM& The first step is hydration of the alke

Question 14

Identify the compound that corresponds to the IR spectrum.

Accepted Answer

A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
E)  compound E 
A)  compound A 
B)  compound B 
C)  compound C 
D)  compound D 
E)  compound E

Question 15

The electron ionization mass spectrum of 1-hexanol barely exhibits a molecular ion peak at m/z 102 due to rapid fragmentation to the next largest fragment at m/z 84. Predict the structure corresponding to the fragment and draw a curved arrow mechanism to show how it is formed.

Accepted Answer

An electron is first lost from the hydro

Question 16

The IR absorption that occurs at the highest wavenumber is

Accepted Answer

A)  the C≡C stretching vibration of 1-butyne. 
B)  the C=C stretching vibration of 1-butene. 
C)  the asymmetric C-O stretching vibration of diethyl ether. 
D)  the =C-H bending vibrations of 1-butene. 
A)  the C≡C stretching vibration of 1-butyne. 
B)  the C=C stretching vibration of 1-butene. 
C)  the asymmetric C-O stretching vibration of diethyl ether. 
D)  the =C-H bending vibrations of 1-butene.

Question 17

These two compounds have similar molecular weights. Explain how to use mass spectrometry to differentiate between the two.

Accepted Answer

Bromine consists of equal amounts of ⁷⁹Br

Question 18

The electron ionization of an unknown neutral compound gives this mass spectrum. Which combination of elements most likely comprises the molecule?

Accepted Answer

A)  two carbons, three hydrogens, and one nitrogen 
B)  three carbons and five hydrogens 
C)  one carbon, five hydrogens, and two nitrogen atoms 
D)  two carbons, four hydrogens, and one nitrogen 
A)  two carbons, three hydrogens, and one nitrogen 
B)  three carbons and five hydrogens 
C)  one carbon, five hydrogens, and two nitrogen atoms 
D)  two carbons, four hydrogens, and one nitrogen

Question 19

A graduate student is cleaning out the refrigerator in the laboratory and stumbles upon an unlabeled beaker in the back. The IR analysis of the compound shows a large broad peak at 3300 cm-1 and no other significant peaks. The electron ionization mass spectrum shows the molecular ion at m/z 100 at 15% relative abundance and an ion at m/z 101 with a 1% relative abundance. Propose a structure for the unknown compound. Hint: Start with the relative abundance data to determine the number of carbons in the molecule.

Accepted Answer

Let's start by comparing the relative ab

Question 20

Typical IR absorptions occur in the 650-3700 cm-1 wavenumber range. These result from energy absorption from IR radiation by
(Pay attention to your units!)

Accepted Answer

A)  molecular vibrations that occur roughly 1013 to 1014 times per second. 
B)  molecular rotations that occur roughly 1013 to 1014 times per second. 
C)  molecular vibrations that occur roughly 10-13 to 10-14 times per second. 
D)  molecular vibrations that occur roughly 1010-1011 times per second 
E)  molecular vibrations that occur roughly 10-11 to 10-12 times per second. 
A)  molecular vibrations that occur roughly 1013 to 1014 times per second. 
B)  molecular rotations that occur roughly 1013 to 1014 times per second. 
C)  molecular vibrations that occur roughly 10-13 to 10-14 times per second. 
D)  molecular vibrations that occur roughly 1010-1011 times per second 
E)  molecular vibrations that occur roughly 10-11 to 10-12 times per second.

Exam 13: Introduction to Spectroscopy

In IR spectroscopy, an absorption occurs any time

What is the energy (in kJ mol-1) of infrared radiation that has a wavenumber of 1600 cm-1? (Planck's constant = 3.99 × 10-13 kJ mol-1 sec; the velocity of light = 3 × 1010 cm sec-1)

A compound with an unknown structure is investigated by determining both its EI (electron ionization) and CI (chemical ionization) mass spectra. Why would you use both and what information is gleaned from each?

Which species shown would not be detected in the electron ionization (EI) mass spectrometry?

The C=C stretching absorption in the IR spectrum occurs at about 1650 cm-1. The C-C stretching vibration occurs but is not observed. Which of these frequencies would be closest to the frequency of the C-C stretching vibration?

The -C≡N stretching frequency in the infrared spectrum occurs at about 2220 cm-1. The C-N stretching frequency should occur at about

Methane (CH4) is vaporized in a vacuum chamber and bombarded with an electron beam of high energy to give the mass spectrum below. (a) Identify each of the labeled m/z peaks. (b) Explain the presence of the small peak at m/z 17.

Select the two true statements.

Which compound has an absorption at 700 cm-1?

Two students perform a hydrolysis reaction on cis-2-pentene. Two alcohols are isolated and one of the students argues that he can prove the structure of each using electron ionization mass spectrometry. Do you agree with his argument? Explain.

Use the structure, including the labels on appropriate protons and bonds, to answer the questions. Please note: Protons are uppercase, bonds are lowercase.

Which molecular vibration does not have an absorption in the IR spectrum?

Outline a synthesis for the transformation. Describe how you could use IR spectroscopy or mass spectrometry to monitor the completion of the reaction.

Identify the compound that corresponds to the IR spectrum.

The electron ionization mass spectrum of 1-hexanol barely exhibits a molecular ion peak at m/z 102 due to rapid fragmentation to the next largest fragment at m/z 84. Predict the structure corresponding to the fragment and draw a curved arrow mechanism to show how it is formed.

The IR absorption that occurs at the highest wavenumber is

These two compounds have similar molecular weights. Explain how to use mass spectrometry to differentiate between the two.

The electron ionization of an unknown neutral compound gives this mass spectrum. Which combination of elements most likely comprises the molecule?

Typical IR absorptions occur in the 650-3700 cm-1 wavenumber range. These result from energy absorption from IR radiation by (Pay attention to your units!)

Chemical Bonding and Chemical Structure

Alkanes and Organic Nomenclature

The Curved-Arrow Notation, Resonance, Acids and Bases, and Chemical Equilibrium

Introduction to Alkenes and Alkynes

Addition Reactions of Alkenes and Alkynes

Principles of Stereochemistry

Cyclic Compounds and Reaction Stereochemistry

Nomenclature and Noncovalent Intermolecular Interactions

The Chemistry of Alkyl Halides

Free-Radical Reactions, Main-Group Organometallic Compounds, and Carbenes

The Chemistry of Alcohols and Thiols

The Chemistry of Ethers, Epoxides, Glycols, and Sulfides

Nuclear Magnetic Resonance Spectroscopy

Dienes and Aromaticity

The Chemistry of Benzene and Its Derivatives

Allylic and Benzylic Reactivity

The Chemistry of Aryl Halides, Vinylic Halides, and Phenols

The Chemistry of Aldehydes and Ketones

The Chemistry of Carboxylic Acids

The Chemistry of Carboxylic Acid Derivatives

The Chemistry of Enolate Ions, Enols, and Α,β-Unsaturated Carbonyl Compounds

The Chemistry of Amines

Carbohydrates

The Chemistry of Thioesters, Phosphate Esters, and Phosphate Anhydrides

The Chemistry of the Aromatic Heterocycles and Nucleic Acids

Amino Acids, Peptides, and Proteins

Pericyclic Reactions

Filters

What is the energy (in kJ mol^-1) of infrared radiation that has a wavenumber of 1600 cm^-1? (Planck's constant = 3.99 × 10^-13 kJ mol^-1 sec; the velocity of light = 3 × 10¹⁰ cm sec^-1)

The C=C stretching absorption in the IR spectrum occurs at about 1650 cm^-1. The C-C stretching vibration occurs but is not observed. Which of these frequencies would be closest to the frequency of the C-C stretching vibration?

The -C≡N stretching frequency in the infrared spectrum occurs at about 2220 cm^-1. The C-N stretching frequency should occur at about

Methane (CH₄) is vaporized in a vacuum chamber and bombarded with an electron beam of high energy to give the mass spectrum below. (a) Identify each of the labeled m/z peaks. (b) Explain the presence of the small peak at m/z 17.

Which compound has an absorption at 700 cm^-1?

Typical IR absorptions occur in the 650-3700 cm^-1 wavenumber range. These result from energy absorption from IR radiation by (Pay attention to your units!)