Orgo 12.1-12.5

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  1. __ is the measurement of the amt. of light absorbed by a compound as a function of the wavelength of light. In general, a __ irradiates the sample with light, measures the amount of light transmitted as a function of wavelength, and plots the results on a graph. Unlike chemical tests most spectroscopic techniques are __; that is, the sample is not destroyed. Many different kinds of spectra can be measured with litle or no loss of sample.
    • absorption spectroscopy
    • spectrometer
    • nondestructive
  2. There are __ spectroscopic or related techniques.
    1) __ observes the vibrations of bonds and provides evidence of the functional groups present.
    2) __ is not a spectroscopic technique because it does not measure absorption or emission of light. A __ bombards molecules with electrons and breaks the molecules into fragments. Analysis of hte masses of the fragments gives the molecular weight, possibly the molecular formula, and clues to the structure and functional groups. Less than a mg of sample is destroyed in the analysis.
    • 4
    • infrared spectroscopy
    • Mass spectrometry x2
  3. 3) __ observes the chemical environments of the hydrogen atoms or the carbon atoms and provides evidence for the structure of the alkyl groups and clues to the functional groups.
    4) __ observes electronic transitions and provides info on the electronic bonding in the sample.
    • nuclear magnetic resonance (NMR) spectroscopy
    • ultraviolet (UV) spectroscopy
  4. These spectroscopic techniques are complementary and they are most powerful when used together. In many cases, an unknown compound can be completely __ from one spectrum without additional information, yet the __ can be determined with confidence using two or more different types of spectra.
    • identified
    • structure
  5. __, __, __, __, and __ are examples of electromagnetic radiation. They all travel at the __, about 3 x 10^10 cm/second but differ in __ and __.

    __ of a wave is the number of complete wave cycles that pass a fixed point in a second. __ is usually given in __, meaning cycles per second. The __ is the distance between any two peaks (or troughs) of the wave.
    • visible light
    • infrared light
    • UV light
    • microwaves
    • radiowaves
    • frequency
    • wavelength
    • frequency x2
    • hertz
    • wavelength
  6. The wavelength and frequency, which are __, are related by the equation __.
    inversely proportional

    • vλ= c
    • where
    • c= speed of lght
    • v= frequency in hertz
    • λ= wavelength in cm
  7. Electromagnetive waves travel as __, which are massless packets of energy. The energy of a __ is proportional to its frequency and inversely proportional to its wavelength. A __ has an energy given by __.
    • photons
    • photon x2
    • E=hv=hc/λ
    • where h is Planck's constant, 6.62 x 10^-37 kJ*sec
  8. Under certain conditions, a molecule struct by a photon may __. In this case, the molecule's eneregy is increased by an amount equal to the phonton's energy, __. For this reason, we often represent the __ of a reaction mixture by a symbol __.
    • absorb the photon's energy
    • hv
    • irradiation
    • hv
  9. The __ is the range of all possible frequencies, from zero to infinity. In practice, the spectrum ranges from the very low radio frequencies used to the very high frequencies of gamma rays. 

    The __ is continuous, and the exact positions of the dividing lines between the different regions are somewhat arbitrary. Energies in the UV-visible range excite electrons to higher energy levels within molecules. __ excite molecular vibrations, and __ excite rotations. __ excite the nuclear spin transitions observed in NMR spectroscopy.
    • electromagnetic spectrum x2
    • Infrared energies
    • microwave energies
    • Radio-wave frequencies
  10. The __ of the spectrum corresponds to frequencies from just below the visible frequencies to just above the highest __ and __: wavelengths of about 8 x 10^-5 cm to 1 x 10^-2 cm. Common __operate in the middle of this region, at wavelengths between .00025 and .0025 cm, corresponding to energies of about 4.6 to 46 kJ moles.
    • infrared region 
    • microwave and radar frequencies
  11. __ do not have enough energy to cause electronic transitions, but they can cause groups of atoms to vibrate with respect to the bonds that connect them. Like __, these vibrational transitions correspond to distinct energies, and molecules absorb __ only at certain wavelengths and frequencies.
    • infrared photons
    • electronic transitions
    • infrared radiation
  12. The position of an __ can be specified by its __, measured as __. A __ corresponds to one millionth of a meter. A more common unit is the __, which corresponds to the number of cycles in a centimeter. The __ is the reciprocal of the wavelength and can be calculated by dividing 10,000 by the wavelngth in microns. The units are __.
    • infrared band
    • wavelength
    • micron
    • wavenumber x2
    • cm^-1
  13. __ have become the most common method for specifying __. The __ is proportional to the frequency of the wave, so it is also proportional to the __ of this frequency.
    • wavenumberes
    • IR absorptions
    • wavenumber
  14. If a bond is stretched, what happens? 

    If a bond is compressed, what happens?

    If it is stretched or compressed and then released, what happens?
    a restoring force pulls the two atoms together toward their equilibrium bond length

    the restoring force pushes the two atoms apart

    the atoms vibrate
  15. The frequency of the stretching vibration depends on the __ and __. __ vibrate more slowly than __. In a group of bonds with similar bond energies, the __. 

    __ are generally stiffer, requiring more force to stretch or compress them. Thus, _ usually vibrate faster than weaker bonds. ___ are stronger than __, so __ vibrate at higher frequencies than __. Similarly, __ vibrate at higher frequencies than __. In a group of bonds having atoms of similar masses, the __.
    • masses of the atoms
    • stiffness of the bond
    • heavier atoms
    • lighter ones 
    • frequency decreases with increasing atomic weight
    • stronger bonds
    • stronger bonds
    • triple bonds
    • double bonds
    • triple bonds
    • double bonds x2 
    • single bonds
    • frequency increases with bond energy
  16. An __ is a graph of the energy absorbed by a molecule as a function of thefrequency or wavelength of light. In the __, absorptions generally result from __. Even with simple compounds, infrared spectra contain many different absorptions not just one absorption for each bond. In a bending vibration, the __ stay constant, but the __ vibrate about their equilibrium values.
    • infrared spectrum 
    • IR spectrum
    • exciting the vibrational modes of the bonds in the molecule
    • bond lengths
    • bond angles
  17. The two O-H bonds can stretch in phase with each other (__) or they can stretch out of phase (__). The H-O-H bond angle can also change in a __, making a __ motion.
    • symmetric stretching
    • antisymmetric stretching
    • bending vibration
    • scissoring
  18. A nonlinear molecule with n atoms generally has __. We also observe __ and __ of these simple fundamental vibrational modes. The number of __in an __ can be quite large, even for simple molecules.
    • 3n-6
    • combos and multiples (overtones) 
    • absorptions 
    • infrared spectrum
  19. It is highly unlikely that the __ of two different compounds will show the same frequencies for all their various complex vibrations. For this reason, the __ provides a __ of a molecule. In fact, the region of the __ containing most of these complex vibrations is commonly called the __ of the spectrum.
    • IR spectra
    • infrared spectrum
    • fingerprint
    • IR spectrum
    • fingerprint region
  20. The simple stretching vibrations in the 1600 to 3500 cm^-1 region are the most characteristic and predictable. 

    Not all molecular vibrations absorb __. To understand which ones do and which ones do not, we need to consider how an __ interacts with a molecular bond. The key to this interaction lies with the __ of the bond, measured as its __. A bond with a dipole moment can be visualized as a __. If this bond is placed in an electric field, it is either __ or __, depending on the direction.
    • infrared radiation
    • electromagnetic field
    • polarity
    • dipole moment
    • positive and negative charge separated by a spring
    • stretched or compressed
  21. One of the components of an electromagnetic wave is a __. This field alternately stretches and compresses a __. When the electric field is in the same direction as the __, the bond is __and its dipole moment __. When the field is opposite the dipole moment the bond __and its dipole moment __. If this __ and __ of the bond occurs at the frequency of the molecule's natural rate of vibration, energy may be __. Vibrations of bonds with dipole moments generally result in __ and are said to be __.
    • rapidly reversing electric field (E with arrow above head)
    • polar bond
    • polar bond
    • compressed
    • decreases
    • stretches 
    • increases
    • alternate stretching and compressing
    • absorbed
    • IR absorptions
    • IR-active
  22. If a bond is symmetrical and has zero dipole moment, the electric field __.

    Because the vibration produces no change in the dipole moment, there is __.

    This vibration is said to be __, and it produces no absorption in the __.

    The key to an __ is that the __.
    does not interact with the bond.

    no absorption of energy

    • IR-inactive
    • IR spectrum

    IR-active vibration

    vibration must change the dipole moment of the molecule
  23. In general, if a bond has a dipole moment, its __ causes an __ in the IR spectrum. If a bond is symmetrically subbed and has zero dipole moment, its __ is weak or absent in the spectrum. Bonds with zero dipole moments sometimes produce absorptions (usually weak) because __, __, and __ make them unsymmetrical part of the time. Strongly polar bonds may absorb so strongly that they also proudce __ peaks, which are relatively small peaks at a multiple of the __.
    • stretching frequency
    • absorption
    • stretching vibration
    • molecular collisions
    • rotations
    • vibrations
    • overtone
    • fundamental vibration frequency
Card Set:
Orgo 12.1-12.5
2013-12-26 15:43:16
CHM 202
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