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Worksheet: Comparing Spectroscopic Methods

Q1:

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.

Q2:

Ultraviolet and visible radiation affect which of the following?

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

Q3:

Infrared radiation affects which of the following?

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

Q4:

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.

Q5:

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.

Q6:

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.

Q7:

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.

Q8:

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.

Q9:

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

Q10:

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.

Q11:

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.