SPIN SPIN coupling, decoupling and shift reagents

SPIN SPIN coupling, decoupling and shift reagents

1. Dept. of Pharmaceutics 1
Seminar on…..
Spin-Spin Coupling
De-Coupling &
Shift Reagent
Presented by:-
NIVEDITHA G
1
st
semMpharm

2. Spin Spin Coupling
Theinteractionbetweenthespinsofthe
neighbouringnucleiinamoleculemaycause
thesplittingoflinesintheNMRspectrum.
Thisphenomenonofsignalsplittingiscalled
SPIN-SPINCOUPLINGorSPLITTING
Thissplittingiscausedbytheinfluenceof
thespinstatesofneighbouringprotons
transmittedthroughchemicalbonds.
Dept. of Pharmaceutics 2

3. Dept. of Pharmaceutics 3

4. Thenumberoflines(multiplicity)observedin
theNMRsignalforagroupofprotonisnot
relatedtonumberofprotoninthatgroup;the
multiplicityoflinerelatedtothenumberof
protoninneighbouringgroup.
Asimplerule(n+1)isusedtofindthe
multiplicity.
n= no. proton in neighbouring group.
Dept. of Pharmaceutics 4

5. SPECTRUM OF ETHYL IODIDE (CH
3CH
2I)--
Dept. of Pharmaceutics 5

6. Methyleneprotonsaresplitintoaquartet(fourpeaks)&
Themethylgroupissplitintotriplet(threepeaks).
Dept. of Pharmaceutics 6

7. Cause of Splitting--
Splittingofsignalcanbedeterminedbytheenvironmentof
theabsorbingprotonwithrespecttoneighbouringproton.
Becauseofdifferentspinstatesofneighbouringprotons,
theactualmagneticfieldexperiencedbygivenprotonmay
bemodifiedinnumberofway.
Absorbingprotonmayexperienceeachofthemodifiedfield
&it’sabsorptionsignalmaybesplitupintodifferentpeaks.
Thisisthespin-spincouplingofabsorbingandneighbouring
protonwhichisresponsibleforsplittingofpeak.
Dept. of Pharmaceutics 7

8. Dept. of Pharmaceutics 8
Fig:-Splitting by one adjacent proton.

9. Dept. of Pharmaceutics 9
Fig:-Splitting by two adjacent proton.

10. Dept. of Pharmaceutics 10

11. Dept. of Pharmaceutics 11

12. Spin-Spin De-Coupling
Theprocessofremovingthespinspinsplitting
betweenspinsofaprotoniscalleddecoupling.
Inthistechnique,radiofrequencysourceisneeded
toirradicatetheprotonatthenecessaryfrequency
&recordingofspectrumisdoneinthesameway,
itiscalled“doubleresonance”or“double
irradiation”
Dept. of Pharmaceutics 12

13. Since multiplet collapses to a singlet in the
process.It is also called spin decoupling.
Irradiate
CH
3 -CH
2 –CH
2OH CH
3–CH
2–CH
2OH
Triplet sextet triplet triplet quartet
Irradiate
CH
3–CH
2-CH
2OH CH
3–CH
2–CH
2OH
Singlet Singlet
Irradiate
CH
3-CH
2-CH
2OH CH
3–CH
2–CH
2OH
Triplet Triplet
Dept. of Pharmaceutics 13

14. 1.Field sweep method:
Inthismethodboththeappliedfrequency(Vl)
&theirradiationfrequency(V2)areKept
constantthemagneticfieldisvarieduntilachara
cteristicchangeoccursinthelinesofparticular-
multiplies.
Dept. of Pharmaceutics 14
METHODS OF DECOUPLING

15. 2.Frequencysweepmethod:
Inthismethodtheappliedmagneticfieldandthe
irradiationfrequency(VI)iskeptconstantandthe
appliedfrequencyisvariedtheirradiation
frequency(V2)bechangedaftereachscan,
permittinganextensiveinvestigationofspinspin
coupling.
Dept. of Pharmaceutics 15

16. Types of decoupling
Off resonance de-coupling.
Proton decoupling or noise decoupling.
Inter nuclear double resonance decoupling
Coherent and broadband decoupling.
Spin tickling
Dept. of Pharmaceutics 16

17. Off resonance de-coupling
Offresonancedecouplingcanbedefineaspartial
decouplingofonetypeofnucleiwhileobservingthe
spectrumofanothertypeofnucleibyapplying
radiofrequencyfieldnotexactlyequaltothelarmour
frequencyofthatnucleusi.e.thesampleisirradiatedata
frequencyclosetobutnotcoincidingwiththeresonance
frequencyofprotonsasaresultthemultipletsbecome
narrowednotremovedalltogetherasinfullydecoupled
spectra.
Dept. of Pharmaceutics 17

18. Irradiatethesampleattwofrequenciesofproton
resonance.
Thefirstfrequencytoaffecttheprotonmagneticresonance
i.e.80MHz.
Thesecondfrequencytoresonanceallprotonatthesame
timeE.g.80MHz.
DecouplingiscarriedoutbyApplingthedecouplingsignal
whichhasalltheH+frequencies(i.e.around80-100Hz)
andtheirforeaformofradiofrequencynoisethusthe
obtainedspectrumisprotondecoupledornoisedecoupled.
Dept. of Pharmaceutics 18
Proton decoupling or noise decoupling

19. Shift Reagent
Shiftreagents,providesausefultechniquefor
spreadingoutPMRabsorptionpatternswhich
normallyoverlap,withoutincreasingthestrength
oftheappliedmagneticfield.
ThePMRspectrumofn-hexanolisreproducedin
figure,whichisnormalrecord.
Dept. of Pharmaceutics 19

20. Whenthesamespectrumisrecordedafterthe
additionofasolubleeuropium(111)complex,Eu
(DMP)3i.e,theshift-reagentthespectrumis
spreadoutoverawiderangeoffrequenciessothat
itisnewsimplifiedalmosttofirstorder.
Dept. of Pharmaceutics 20

21. Dept. of Pharmaceutics 21

22. REFEREENCES
Y.R. Sharma. Elementary Organic
Spectroscopy. 4
th
Ed. 2008;201-32.
G.R. Chatwal. Instrumental methods of
chemical analysis.5
th
Ed. 2008;2.198-2.202.
Internet sources.
Dept. of Pharmaceutics 22

23. Dept. of Pharmaceutics 23
THANKS