3. INTRODUCTION
⚫Nuclear magnetic resonance Spectroscopy isa
powerful analytical technique used tocharecterise
organic molecule by identifying Carbon-Hydrogen
frameworks with in molecule.
⚫Twotypesof NMR Spectroscopyare used to
charecterise organic structure :-
⚫H-1 NMR :-Todetermine the typeand numberof H
atoms in a molecule.
⚫C-13 NMR:- Used todetermine typeof carbon atoms in
the molecule.
4. HISTORY
⚫NMR was firstdescribed
and measured in molecular
ISIDOR RABI in 1938 by
⚫extending the Stern-
Gerlach experiment
⚫In 1944 RABI wasawarded
the Nobel Prize in Physics.
ISIDOR ISAAC RABI
RABI, Photographed in 1944
5. PRINCIPLE
⚫ Nuclear magnetic resonance concern
the magnetic properties of certain
atomic nuclei.
⚫ It concern the atom having spin quantum number.
⚫ C-12 nucleus is not magnetic active because
; C-12:- Proton 6 ,Neutron 6
Nuclear
spin (I)=0 C-13:-
Proton
6,Neutron 7
Nuclear spin (I)=1/2
⚫ Relatively new technique as compared to proton NMR.
6. C-13 NMR
⚫C-12 have no magneticspin and produce no NMR
signal.
⚫C-13 have magneticspin(I)=1/2
⚫C-13 account foronly 1.1%of naturallyoccurring
carbon.
Nocoupling between C-13 and C.
C-13 haveweak signal.
C-13 havestrong coupling with H.
C-13 haveweak coupling with C.
7. C-13 NMR
⚫C-13 has onlyabout 1.1% natural abundance (of carbon
atoms).
⚫C-12 does notexhibit NMR behavior.
⚫Asa result, C is about 400 times less sensitive than H
nucleus to the NMR phenomena.
⚫Chemical shift range is normally 0 to 220ppm.
⚫Normal C-13 Spectraare “broadband, proton
decoupled”so the peaks showas single lines.
⚫Numberof peak indicates the numberof typeof
Carbon atoms.
8. WHY C-13 NMR REQUIRED
⚫Carbon NMR can used todetermine the numberof
non-equivalentcarbon and no identify the typesof
carbon atoms (methyl,methylene,aromatic ,carbonyl
)which maypresent in compound.
⚫C13 Signal are spread overa much widerrange than
proton signal making iteasier to identifyand counts
individual nuclei.
9. CHEMICAL SHIFT
⚫In contrast to the small range of chemical shift in H-1
NMR (0-10ppm), C-13 NMR absorption
occursovera much broader range (0-220ppm).
⚫The chemical shift reference standard for C- 13 is the
carbon in TMS whose chemical shift is considered top
be 0.0ppm.
12. SPIN SPIN SPLITTING OF
C-13 NMR
⚫Homonuclearspin spin splitting:-
Becauseof its low natureabundance
there is a low probabilityof finding two C-13 atom next
toeach other in a single molecule.
C-13 –C-13 Coupling negligible
⚫Heteronuclearspin spin splitting:-
C-13 will magneticallycouplewith attached
protonand adjacentproton, N+1 rule is obeyed.
13. ⚫Splitting takeplaceaccording to 2nI+1 rule
Where n=no. of nuclei
I=spinquantum number
CH3=3+1=4 quartet
CH2=2+1=3 triplet
CH=1+1=2 doublet
C=0+1=1 singlet
18. ⚫Hybridization –
-sp3 C signal is in the range 0-90
-sp2 C signal is in range 110-220
-C=O signal is at the low-field end in the range 160-220
19. APPLICATION
⚫C-13 NMR has elucidated and biochemical structure.
⚫C-13 NMR provides information about the backbone to
moleculerather than periphery.
⚫C-13 nuclei are stable isotopesand hence it notdanger
toradiotracer.
⚫And also used forquantification of drug purity to
determination of the compositionof high molecular
weight synthetic polymer.
20. REFERENCES
⚫McCash M. Elainand Banwell N.Colen “fundamental
of molecularspectroscopy,”4th edittion,
TataMcGrawHill publishing company LTD.New
Delhi.page no-234-240.
⚫Chatwal R. Gurdeepand Anand K. Sham,”Intrumental
method of chemical analysis,”Himalaya publishing
house mumbai, Delhi. page no. 2.231.
⚫H. Kour by Spectroscopy ,12th eddi. Pragati
publication,page no. 415-424.
