NMR spectroscopy in solids: A comparison to NMR spectroscopy in liquids - PowerPoint PPT Presentation

Loading...

PPT – NMR spectroscopy in solids: A comparison to NMR spectroscopy in liquids PowerPoint presentation | free to view - id: 427d65-NzgxZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

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

Description:

NMR spectroscopy in solids: A comparison to NMR spectroscopy in liquids Mojca Rangus Mentor: Prof. Dr. Janez Seliger Comentor: Dr. Gregor Mali Introduction NMR ... – PowerPoint PPT presentation

Number of Views:1063
Avg rating:3.0/5.0
Slides: 23
Provided by: moj9
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

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


1
NMR spectroscopy in solids A comparison to NMR
spectroscopy in liquids
  • Mojca Rangus
  • Mentor Prof. Dr. Janez Seliger
  • Comentor Dr. Gregor Mali

2
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

3
(No Transcript)
4
Magnetization and magnetism
  • Nuclear magnetic moment
  • When magnetic field is applied, starts
    to precess around its 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

5
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

6
NMR periodic table
7
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

8
Spin echo
  • With a special pulse sequence the magnetic
    moments are gathered before the recording starts
  • An efficient method to avoid dead time problem

9
Types of interaction
  • Zeeman interaction
  • Chemical shift
  • Direct dipole coupling
  • Indirect dipole coupling or J-coupling
  • Quadrupolar interaction

10
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

11
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

12
(No Transcript)
13
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

14
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

15
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

16
Solution-state NMR spectrum
17
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

18
Powder spectra
  • All orientations of the molecules are presented
    equally
  • Resonance lines become extremely broad
  • Anisotropic nature of the interactions comes
    fully into account

19
Magic angle spinning
  • Spinning the sample under the magic angle
    considerably narrows the resonance lines

static
MAS
solution
20
Decoupling
static
  • In the mechanism of decoupling a strong rf field
    is applied so that magnetic moments are flipped
    randomely back and forth to narrow the
    anisotropic broadeneng of the resonance lines

static with low power decoupling
static with high power decoupling
decoupling MAS
solution-state spectrum
21
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

22
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
About PowerShow.com