It contains what are the shift reagents, and how they will use in NMR spectroscopy. It includes lanthanide shift reagents and their effect using NMR spectroscopy. It has mostly used shift reagents like Europium and their importance. paramagnetic species that affect the NMR spectra are also explained in detail. What are contact shift and pseudo-contact shift also explained. It contains what are the chiral shift reagent, and the advantages, and disadvantages of lanthanide shift reagents. Reference books are also included.

1. SHIFT REAGENTS
Presented By:
K. Muthu Kannan
II M.Sc.,Chemistry
S.B.K.College
Aruppukottai.

2.  Complex spectra
 Shift reagents
 History
 Paramagnetic materials
 Contact shift
 Pseudo-contact shift
 Chiral shift reagents
 Advantages
 Disadvantages
2
CONTENTS

3. COMPLEX SPECTRA
3

4. 4
COMPLEX SPECTRA

5. 5
SHIFT REAGENTS

6. Shift reagents were first introduced by Hinckley in 1969.
Shift reagents provide a useful method for spreading out normal
NMR absorption pattens without increasing the strength of the
applied magnetic field.
The shift reagents are usually enolic ß-dicarbonyl complexes of a
rare earth (lanthanide) metals and these complexes are mild Lewis
acids.
Europium is probably the most commonly used metal for shift
reagents. Two of its widely used complexes are Eu(dpm)3 and
Eu(fod)3.
6
HISTORY

7. 7
MOSTLY USED SHIFT REAGENTS

8. 8
OTHER SHIFT REAGENTS
Pirkle’s alcohol TRISPHAT –
tris(tetrachlorocatecholato)phosphate(-1)

9. 9
RARELY USED SHIFT REAGENTS

10.  Complexes of europium, erbium, thulium and ytterbium shift resonances to down
field (larger δ).
 Complexes of cerium, praseodymium, neodymium, samarium, terbium and
holmium generally shift resonances to up field (lower δ).
 Olefins and arenes do not show Lanthanide shift reagents induced shifts since they
cannot form complexes with the lanthanide ion.
 These lanthanide complexes produce spectral simplifications in the NMR
spectrum of any compound with a relatively basic pair of electrons (an unshared
pair) which can coordinate with Eu3+. Typically aldehydes, ketones, alcohols,
thiols, ethers and amines all interact.
 The fully deuteriated derivative of Eu(fod)3 is also commercially available, and
this eliminates the signals from ligand protons.
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IMPORTANTS OF SHIFT REAGENTS

11. 11
EFFECT OF LANTHANIDE SHIFT REAGENT

12.  Paramagnetic materials by shortening relaxation times cause line broadening.They
also cause a shift in signals.
 Co and Ni cause several line broadening thus cannot be used.
 Lanthanide ions are found to cause line broadening.
 Europium and praseodymium are an extraordinary exception giving a very low shift
broadening.
 The NMR spectrum of paramagnetic compounds cannot be obtained because the
unpaired electrons broaden the spectrum by both electron spin - nuclear spin
coupling mechanism.
12
PARAMAGNETIC MATERIALS

13. Contact shifts result from spin polarization conveyed through the molecular
orbitals of the molecule.
The origin of contact shift can be understood if we consider coupling between
the electron and the nucleus, which would give a doublet in the NMR spectrum
under conditions of slow electronic spin-lattice relaxation, but with a large
(millions of Hz) coupling constant.
With such a large coupling, the intensities of the two resonances are not equal, so
their weighted mean position is not mid way between them.
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CONTACT SHIFT

14. 14
 Under fast relaxation conditions the doublet collapses back to a singlet at
the weighted mean position, and so may fall some thousands of Hz away
from the expected position.
 Contact shifts give a measure of unpaired spin density at the resonating
nucleus, and so are particularly useful in studying the spin distribution in
radical species, or in ligands in organometallic compound.
CONTACT SHIFT

15. 15
PSEUDO-CONTACT SHIFT
 There is a through-space dipolar interaction between the magnetic moments of the
electron and the resonating nucleus, which gives a dipolar shift, also some times
known as a pseudo-contact shift.
 The chemical shift is caused by the dipolar coupling between the magnetic
moments of the nucleus and of the unpaired electron.
 This situation is some what similar to the case of j-coupling where we would
expect the NMR peak to split into a doublet due to the coupling with the magnetic
moment of the unpaired electron.

16. 16
Lanthanide complexes give shifts primarily by the pseudo-contact
mechanism.
The principal factor is the distance between the metal ion and the proton;
the shorter the distance, the greater the shift obtained. On the other hand,
the direction of the shift depends on the lanthanide complex used.
PSEUDO-CONTACT SHIFT

17. 17
EFFECT OF LANTHANIDE SHIFT REAGENT

18. 18
EFFECT OF LANTHANIDE SHIFT REAGENT

19. 19
A chiral shift reagents is a reagent used in analytical chemistry for determining
the optical purity of a sample.
Compounds must contain Lewis bases.
Some of the more effective reagents developed are Eu(facam)3 (tris(3-
trifluoroacetyl-d-camphorato)europium(III)) and Eu(hfc)3 (tris(3-
heptafluoropropylhydroxymethylene)-d-camphorato)europium(III).
CHIRAL SHIFT REAGENTS

20. 20
 Often sufficient separation between the R and S enantiomers can be obtained
so that the enantiomeric purity can be determined directly by NMR
integration.
CHIRAL SHIFT REAGENTS

21. 21
EFFECT OF CHIRAL SHIFT REAGENTS

22. Give spectra which are much easier to interpret.
More easily obtained, don’t require high frequency instruments.
Identifying enantiomeric mixtures in solution.
No chemical manipulation of the sample required with the use of shift
reagents.
Shift reagents cause a small amount of line broadening.
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ADVANTAGES
DISADVANTAGES

23. Organic spectroscopy by L.D.S.Yadav.
Introduction to spectroscopy by Pavia 4th edition.
Organic spectroscopy by Willam kemp 3rd edition.
https://www.researchgate.net/figure/Commonly-used-shift-reagents-top-and-first-
generation-commercial-contrast-agents-for_fig1_37428740
https://inis.iaea.org/collection/NCLCollectionStore/_Public/05/125/5125697.pdf
https://organicchemistrydata.org/hansreich/resources/nmr/?page=08-tech-07-
lis%2F
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REFERENCES