C-13 NMR Spectroscopy

C-13 Nuclear Magnetic Resonance Spectroscopy

1. C-13 NMR SPECTROSCOPY By- Manish Sahu M.Sc. Chemistry (Final) Sp.- Physical Chemistry

2. C-13 NMR SPECTROSCOPY CONTENS INTRODUCTION HISTORY PRINCIPLE C-13NMR WHY C- 13 NMR REQUIRED CHEMICAL SHIFT NUMBER OF SIGNAL SPIN SPIN SPLITTING OF C- 13 NMR FACTOR AFFECTING C- 13 NMR APPLICATION REFERENCES

3. INTRODUCTION Nuclear magnetic resonance Spectroscopy is a powerful analytical technique used to charecterise organic molecule by identifying Carbon-Hydrogen frameworks with in molecule. Two types of NMR Spectroscopy are used to charecterise organic structure :- H- 1 NMR :-To determine the type and number of H atoms in a molecule. C- 13 NMR:- Used to determine type of carbon atoms in the molecule.

4. HISTORY NMR was first described and measured in molecular ISIDOR RABI in 1938 by extending the Stern- Gerlach experiment In 1944 RABI was awarded 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 magnetic spin and produce no NMR signal. C- 13 have magnetic spin(I)=1/2 C- 13 account for only 1.1%of naturally occurring carbon. No coupling between C- 13 and C. C-13 have weak signal. C-13 have strong coupling with H. C-13 have weak coupling with C.

7. C-13 NMR C-13 has only about 1.1% natural abundance (of carbon atoms). C-12 does not exhibit NMR behavior. As a 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 Spectra are “broadband, proton decoupled”so the peaks show as single lines. Number of peak indicates the number of type of Carbon atoms.

8. WHY C - 13 NMR REQUIRED Carbon NMR can used to determine the number of non-equivalent carbon and no identify the types of carbon atoms (methyl,methylene,aromatic ,carbonyl )which may present in compound. C13 Signal are spread over a much wider range than proton signal making it easier to identify and 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 occurs over a 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.

10. NUMBER OF SIGNALS

11. SPIN SPIN SPLITTING OF C-13 NMR Homonuclear spin spin splitting :- Because of its low nature abundance there is a low probability of finding two C-13 atom next to each other in a single molecule. C-13 –C-13 Coupling negligible Heteronuclear spin spin splitting :- C-13 will magnetically couple with attached proton and adjacent proton, N+1 rule is obeyed.

12. Splitting take place according t o 2 nI+1 rule Where n=no. of nuclei I=spin quantum number CH 3 =3+1=4 quartet CH 2 =2+1=3 triplet CH=1+1=2 doublet C=0+1=1 singlet

13. 2 – bromo butane

14. FACTOR AFFECTING OF C- 13 NMR Electro Negative of nearby atoms – C bonded to O,N or halogen absorb downfield because O,N,and halogen pull electron away from nearby C-13 atoms, decreasing their electron density and “deshielding” them.

15. Effect and chain length:- Cl-CH 2 -CH 2 -CH 2 -CH 2 -CH 3 Chemical shift 45 33 29 22 14 (Delta value) Deshielding effect of Cl decreases as number of bonds between Cl and C increases .

16. 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

17. APPLICATION C- 13 NMR has elucidated and biochemical structure. C-13 NMR provides information about the backbone to molecule rather than periphery. C-13 nuclei are stable isotopes and hence it not danger to radiotracer. And also used for quantification of drug purity to determination of the composition of high molecular weight synthetic polymer.

18. REFERENCES McCash M. Elain and Banwell N.Colen “fundamental of molecular spectroscopy,”4 th edittion, TataMcGrawHill publishing company LTD.New Delhi.page no-234-240. Chatwal R. Gurdeep and Anand K. Sham ,”Intrumental method of chemical analysis,”Himalaya publishing house mumbai, Delhi. page no. 2.231. H. Kour by Spectroscopy ,12 th eddi. Pragati publication,page no. 415-424.