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Flashcards

NMR

Ashlin Deatherage instrumental analysis GRE English 37 cards

Cards in this deck (37)

  1. 1Molecular environment influences the absorption of___ _____ ______ by a nucleus in a magnetic field and can be correlated to molecular structure.radio frequency pulse
  2. 2an atoms electrons have an inherent 'spin', as well as the nucleus, this is based onthe electrons and nucleui’s angular momentum
  3. 3Spin is quantized in integral and half-integral multiples of h/2pih/2pi or h-bar
  4. 4The value of the nuclear spin depends on the number of _______ (Z) and its _______(protons + neutrons)protons
    mass
  5. 5Nuclear spin quantum number (I) determines number of spin states. how do u calc the number of spin states# spin states = 2I + 1
  6. 6Spin states are ________ in energy in the absence of a magnetic fielddegenerate
    Interaction with a magnetic field removes the degeneracy.
  7. 7if the number of protons is equal to the number of neutrons, the spin isno spin
  8. 8if there is an odd number of protons OR neutrons, the spin is1/2 integral
  9. 9if there are an odd number of protons AND neutronsthe spin is a whole number
  10. 10• Because the nucleus is charged, its “spin” gives rise itself to amagnetic field
  11. 11• Absorption of radiation changes the alignment of the nuclear moment in the presence of a _____ ______magnetic field
  12. 12the signal intensity is proportional tomagnetic field strength
  13. 13During the absorption or emission process the ____ ___ __________ must change to oppose the magnetic field.angle of precession
  14. 14In order to flip the angle of precession, we induce a ____ ___ to the precessing dipole.force 90°
  15. 15Pulsed NMR is different from other forms of spectroscopy in that we do not measure the:direct absorption or emission of energy
  16. 16spin aligned with the magnetic feild is _____ energy than spin opposed to the magnetic feildlower
  17. 17each electrically unique nuclei will have a differentmagnetic moment and angle of precession
  18. 18nuclei must release a energy as a photon in anon-radiative way
  19. 19T1 relaxationenergy is released to a lattice, as vibrations that increase the temp of the sample
  20. 20T2 relaxationenergy is transferred intermolecularly, to adjacent nuclei, therefore the Boltzmann distribution doesnt change, nuclei stay in their excited state. Shortens the lifetime of the magnetic moment the nuclei was in.
  21. 21When the sample mobility is high, the interaction between the nuclei and lattice decreases T1and causesline broadening.
  22. 22what can cause line broadening in a magnetvariations in the magnetic feild, it can be corrected with shimming
  23. 23why are NMR magnets cooledto increase the conductivity of the superconducting wire
  24. 24Amount of shielding is determined by the:electron density and distribution around the nucleus.
  25. 25Shielding _____ the amount of magnetic field felt by a nucleusreduces
  26. 26dimagneticopposes the magnetic feild
  27. 27paramagneticsupports the magnetic feild
  28. 28Shielding decreases as the electronegativity of _______ groups increaseadjacent
  29. 29• J-splitting or spin-spin splitting is caused by:magnetic moments associated with adjacent nuclei
  30. 30Coupling of magnetic moments is through:the bonding electrons.
  31. 31The coupling constant (J) is a measure of how strongly a nucleus is affected by:the spin of its neighbor
  32. 32If the spins are paired and aligned with the applied field, the effective field is increased causing a :“downfield” shift (higher oscillator frequency).
  33. 33If the spins are paired and opposed to the applied field, the effective field is decreased, requiring a :higher field to bring the nucleus into
    resonance. "upfield" shift
  34. 34Splitting by neighbors or multiplicity of peaks follows(n+1) rule.
  35. 35Acidic protons (e.g. alcohols, acids, etc…) are effectively decoupled from adjacent nuclear magnetic moments when the exchange frequency is rapid compared to :the J-coupling frequency.
  36. 36Homonuclear decoupling:commonly used in 1H spectra,
    simplifies the spectrum by removing splitting
  37. 37Heteronuclear decoupling:The protons are saturated during
    the acquisition of the FID. This causes the heteronuclear spin multiplets to collapse unto a single peak.

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GRE instrumental analysis Flashcards on NMR, created by Ashlin Deatherage on 28/03/2023.
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