NMR spectroscopy in solids: A comparison to NMR spectroscopy in

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					NMR spectroscopy in solids:
A comparison to NMR
spectroscopy in liquids

Mojca Rangus

Mentor: Prof. Dr. Janez Seliger
Comentor: Dr. Gregor Mali
Introduction

   NMR specrtometer
   Basics of NMR
   Types of interaction (concentrate on: spin ½
    nuclei, diamagnetic compounds)
   Solution-state spectra
   Solid-state spectra
   Methods for improving solid-state NMR spectra
Magnetization and magnetism
   Nuclear magnetic moment
   When magnetic field       is applied,  starts to
    precess around it’s direction with Larmor
    frequency
   We describe the movement of the magnetic
    moment with equation


   It is conventent to go from lab. frame to
    rotating frame, which rotates around
    direction with the same frequency that
    precesses:
NMR
   We observe the total magnetization of the sample

   Magnetization is fliped in xy plane with the aid of rotating
    radiofrequency (rf) field


   Projection of the magnetization on the xy plane is then recorded
   The nuclei with nonzero spin (nonzero magnetic moment) can be
    observed
NMR periodic table
Single pulse
   The same coils are used for excitation and recording
   After a pulse a delay is needed before the start of the recording
   From recorded signal (FID) a spectrum is obtained with Fourier
    transormation
   This means that the magnetic moments are alredy scattered in xy
    plane
Spin echo
   With a special pulse sequence
    the magnetic moments are
    gathered before the recording
    starts
   An efficient method to avoid dead
    time problem
Types of interaction

   Zeeman interaction
   Chemical shift
   Direct dipole coupling
   Indirect dipole coupling or J-coupling
   Quadrupolar interaction
Zeeman interaction
   It can be described with a Hamiltonian



    or in ternsor form

   In the magnetic field the two spin states
    have different energies



   It is far the strongest interaction and all
    other types of interaction can be
    considered as corrections
   Order of the magnitude:
Chemical shift
   Indirect interaction of the nuclear spins with
    the external magnetic field through the
    surrounding electrons
   If the electronic environment of nuclei differ,
    the local mag. fields differ and therefore the
    resonance frequencies are different
   Contains information about electronic states
   Chemical shifts also depend on the
    orientation of the molecule in the magnetic
    field
Direct dipole coupling
   Two neighbouring nuclei are coupled through their magnetic dipole
    moments




   Useful for molecule structure studies and
    provides a good way to estimate distances
    between nuclei and hence the geometrical
    form of the molecule
J-coupling
   Nuclear spins are coupled with the help of the molecular electrons
   It is exclusively intramolecular
   The mechanism responsible for the multiplet structure
   It can be viewed only in solution-state NMR spectra where the
    spectral lines are narrow enough to observe the interaction
Electric quadrupole coupling
   Nucleus with the electric quadrupole moment intarects strongly
    with the electric field gradients generated by surrounding
    electron clouds




   Quadrupole interaction is totaly averaged
    in liquids, but in solids is the strongest after
    Zeeman
   In solids we often need to take into account
    second order contributions
Solution-state NMR spectrum
Single crystal spectra
   All interactions are orientation dependent
   Therefore it is possible to conduct NMR
    experiments in similar way as X-ray
    diffraction
   From single crystal spectra it is possible to
    reconstruct the interaction tensors and from
    there the electronic and geometric
    characteristics of the compound
Powder spectra
   All orientations of the molecules are
    presented equally
   Resonance lines become extremely
    broad
   Anisotropic nature of the interactions
    comes fully into account
Magic angle spinning
   Spinning the sample under the magic angle
    considerably narrows the resonance lines




                                                static



                                                MAS



                                                solution
Decoupling
                                      static
   In the mechanism of
    decoupling a strong rf field is
    applied so that magnetic
                                      static with low
    moments are flipped
                                      power decoupling
    randomely back and forth to
    narrow the anisotropic
                                      static with high
    broadeneng of the resonance
                                      power decoupling
    lines


                                      decoupling + MAS


                                      solution-state
                                      spectrum
Cross polarization (CP)
   Cross polarization (CP) is one of
    the most important techniques in
    solid-state NMR
   Polarization from abundant spins
    is transferred to dilute ones via
    the direct diploe coupling
Summary
   Basic principles of NMR
   Viewed the most important type of interactions
    that are encountered in a compound
   Similarities and differences of solution-state and
    solid-state spectra
   The most important techniques used to improve
    powder NMR spectra

				
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