Worksheet: Comparing Spectroscopic Methods
In this worksheet, we will practice comparing the applications of spectroscopic methods and the processes responsible for the production of signals.
What does proton NMR tell you, primarily, about a molecule?
- AWhether there are any hydrogens present in the molecule and what their chemical shift is with respect to a standard (TMS)
- BThe kind of heteroatoms near the hydrogens you observe in the spectrometer
- CThe kind of hydrogens present (what each kind is bonded to) and exactly how many there are relative to each other
- DWhether electron-donating or electron-withdrawing groups are present in the molecule
Which of the following is an accurate definition of mass spectrometry?
- ACareful weighing of molecules using supersensitive nanobalances constructed with microlithography
- BThe breakdown and ionization of molecules with high-energy electrons, followed by magnetic separation of the charged fragments and analysis of their mass-to-charge ratios
- CAnalysis of the charges of molecular ions produced by fragmentation of molecules in a magnetic field
- DAnalysis of the masses of whole molecules that have been given an electric charge using a voltameter
What does the combination of broad peaks and sharper ones that UV spectroscopy generally shows tell us?
- AHow many heteroatoms are in the molecule
- BThe degree of conjugation ( electron delocalization) and something about substitution patterns
- CWhat atoms are attached to a double bond or aromatic ring
- DWhat the elemental composition of the molecule is
How is infrared spectroscopy different from UV-vis and NMR spectroscopies?
- AInfrared spectroscopy overlaps with UV-vis spectroscopy in the electromagnetic spectrum, providing complimentary information on functional groups, while NMR looks at electronic configuration and bonding.
- BInfrared spectroscopy detects vibrational motions of functional groups whereas UV-vis spectroscopy sees electronic transitions and NMR spectroscopy looks at the nuclear magnetic moment transition energy.
- CThey all see different parts of the molecule, and, specifically, different atoms and how they’re joined together.
- DIt uses a different energy range from UV-vis spectroscopy but the same range as NMR spectroscopy.
Which of the following best describes the relative interaction energies used in various kinds of spectroscopic methods?
- ANMR < IR < UV-Vis ≤ mass spectrometry
- BThe energy used does not matter since this can vary independently of frequency or wavelength.
- CNMR < UV-Vis < mass spectrometry < IR
- DYou cannot compare the energies since each type of spectroscopy uses a unique mixture of frequencies.
Which of the following is a general description of spectroscopic methods?
- AThe excitation of molecules with heat or light so that they emit vibrational energy that can be detected with spectrometers
- BThe use of visible or ultraviolet light to illuminate molecules so that they can be observed using a microscope
- CThe use of electromagnetic waves to change the shape or structure of molecules so that they can be observed using a microscope
- DThe measurement of chemical interactions with electromagnetic waves to obtain information about molecular structure and properties
Infrared was one of the first spectroscopic methods and is still widely used today to characterize molecules because:
- AIt is easy to do, takes very little sample and gives specific information about what functional groups are present in the molecule.
- BIt tells you more about the molecule than any other technique.
- CIt uses the least expensive analytical equipment available.
- DYou can sample solids, liquids or gases although the information obtained is not useful without combining with other techniques of analysis.
Which of the following is true for ultraviolet spectroscopy?
- AWe can see the broad peaks in the spectrum given by ionized fragments, and this tells us what kinds of bonds are involved.
- BIt is most sensitive to carbonyl bonds and less sensitive to aromatic and conjugated double bonds.
- CAll types of bonding can be detected, from bonds to bonds, to conjugated and aromatic bonding.
- DDouble bonds, aromatic rings, and conjugated unsaturation can be detected.
Which of the following information about a molecule is determined mainly using infrared spectroscopy?
- AThe exact kind and number of each functional group in the analyte.
- BIts purity and what kinds of impurities are present in the mixture.
- CThe total number of atoms and what kind of them is in the molecule.
- DWhat kinds of functional groups like amides, ethers, and alkene double bonds are present in the molecule.