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Worksheet: Comparing Spectroscopic Methods


How is infrared spectroscopy different from UV-Vis and NMR spectroscopies?

  • A Infrared spectroscopy overlaps with UV-Vis spectroscopy in the electromagnetic spectrum, providing complimentary information on functional groups, while NMR looks at electronic configuration and bonding.
  • BIt uses a different energy range from UV-Vis spectroscopy but the same range as NMR spectroscopy.
  • CThey all see different parts of the molecule, and specifically, different atoms and how theyโ€™re joined together.
  • DInfrared spectroscopy detects vibrational motions of functional groups while UV-Vis spectroscopy โ€œseesโ€ electronic transitions, and NMR spectroscopy looks at the nuclear magnetic moment transition energy.


Ultraviolet and visible radiation affect which of the following?

  • ANuclear spin
  • BCore electrons
  • CMolecular vibrations
  • DValence electrons
  • EMolecular rotations


Infrared radiation affects which of the following?

  • AValence electrons
  • BCore electrons
  • CMolecular rotations
  • DMolecular vibrations
  • E Nuclear spin


Infrared spectroscopy is used mainly for determining what about a molecule?

  • 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 each are in the molecule.
  • DWhat kinds of functional groups like amides, ethers and alkene double bonds are present in the molecule.


Infrared was one of the first spectroscopic methods and is still widely used today to characterize molecules because:

  • AIt tells you more about the molecule than any other technique.
  • BYou can sample solids, liquids or gases although the information obtained is not useful without combining with other techniques of analysis.
  • CIt uses the least expensive analytical equipment available.
  • DIt is easy to do, takes very little sample and gives specific information about what functional groups are present in the molecule.


UV spectroscopy generally shows a combination of broad peaks and sharper ones that tell us what?

  • AHow many heteroatoms are in the molecule.
  • BWhat atoms are attached to a double bond or aromatic ring.
  • CWhat the elemental composition of the molecule is.
  • DThe degree of conjugation ( ๐œ‹ electron delocalization) and something about substitution patterns.


Which of the following is a general description of spectroscopic methods?

  • AThe use of visible or ultraviolet light to illuminate molecules so that they can be observed using a microscope.
  • BThe use of electromagnetic waves to change the shape or structure of molecules so that they can be observed using a microscope.
  • CThe excitation of molecules with heat or light so that they emit vibrational energy that can be detected with spectrometers.
  • DThe measurement of chemical interactions with electromagnetic waves to obtain information about molecular structure and properties.


Which of the following is an accurate definition of mass spectrometry?

  • AAnalysis of the charges of molecular ions produced by fragmentation of molecules in a magnetic field.
  • BAnalysis of the masses of whole molecules that have been given an electric charge using a voltameter.
  • CCareful weighing of molecules using super-sensitive nano-balances constructed with microlithography.
  • DThe 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.


Which of the following best describes the relative interaction energies used in various kinds of spectroscopic methods?

  • AYou cannot compare the energies since each type of spectroscopy uses a unique mixture of frequencies.
  • B NMR < UV-Vis < mass spectrometry < IR
  • CThe energy used does not matter, since this can vary independently of frequency or wavelength.
  • DNMR < IR < UV-Vis โ‰ค mass spectrometry


Ultraviolet spectroscopy looks at what kinds of molecular segments?

  • AWe can see the fragments that give us broad peaks or humps in the spectrum and this tells us what kinds of bonds are involved.
  • BAll types of bonding from ๐œŽ bonds to ๐œ‹ bonds to conjugated and aromatic bonding.
  • CIt is most sensitive to carbonyl bonds and less to aromatic and conjugated double bonds.
  • DDouble bonds, aromatic rings and conjugated unsaturation, and non-bonded heteroatoms all absorb in the UV spectrum and can be detected.


The primary purpose of proton NMR is to tell you what about a molecule?

  • AWhether electron-donating or withdrawing-groups are present in the molecule.
  • BWhether there are any hydrogens present in the molecule and what their chemical shift is with respect to a standard (TMS).
  • CWhat kind of heteratoms are near the hydrogens you observe in the spectrometer.
  • DWhat kind of hydrogens are present (what each kind is bonded to) and exactly how many there are relative to each other.