CARBON NMR M.PHARMA CHEMISTRY MPC201T and MPC101T .pptx

NMR - Carbon 13 NMR M.Pharma Chemistry MPC201T Advanced Spectral Analysis MPC101T Modern Pharmaceutical Analytical Techniques B.PHARMA BP811ET Advanced Instrumentation Techniques

Content Includes - Principle , Chemical Shift , Spin - Spin Coupling , Splitting , Coupling Constant , DEPT Spectra

1. CARBON 13 NMR CHEMISTRY PULKIT MAHESHWARI M.Pharma 2 nd Sem Pharmaceutical Chemistry

2. INTRODUCTION Mass No. is odd in 13 Carbon , NMR Active , Protons = 6 , Neutrons =7 , I = 1/2 Mass No. is odd in 12 Carbon , NMR Inactive , Protons = 6 , Neutrons =6 , I = 0 Relatively new technique as compared to Proton NMR. Natural occurance / abundance of 13C is 1.11% and 12C is 98.89% . Due to less percentage of 13 C , it is less sensitive & quantity of sample required is higher .

3. PRINCIPLE Proton is present in nucleus of the atom and acts as a magnetic bar. When external magnetic field will be applied , protons will be aligned / parallel. Electromagnetic radiation will be applied & resonance take place , 13 C NMR Signal occurs.

4. 13C has lower gyromagnetic ratio as compared to Proton , which one fourth of proton. 1H , Y = 267.53 radians/sec-Tesla 13C , Y = 67.28 radians/sec-Tesla V = (Y/2 π )Bo Where, V = radio frequency Bo = applied magnetic field Y = gyromagnetic ratio IF , Bo = 1.41T/14100G , V = 15.1MHz Bo = 2.35T/23500G , V = 25.2MHz Bo = 4.75T/47500G , V = 50.9MHz Analyst will get direct information about carbon skeleton but in proton NMR analyst will get indirect information. It gives information about carbon atoms. Chemical Shift Value ( δ ) ranges from 0 to 200ppm in 13 C NMR. It is approximately 20 times greater than Proton NMR.

5. Chemical Shift value (δ) ranges from zero to 200 ppm.

6. Number of Signals in carbon 13 NMR Number of equivalent set of carbon present in the sample. Each signal in the 13 carbon NMR represent the equivalent set of carbon atoms. Carbon atom present in the same environment gives the single Signal.

7. Spin-Spin coupling in 13 carbon NMR and Splitting When spin of 13 carbon NMR coupled with proton , then it is known as Proton coupled spectra. Splitting occur due to directly bonded protons. Coupling constant (J) in carbon 13 NMR Coupling constant value will be more than 115 Hertz if directly coupled with proton. -CH3(115-125Hz) , -CH2(150-170Hz) , -CH(240-270Hz).

8. DEPT Spectra Destortionless enhancement by polarization transfer. Used to differentiate between primary , secondary , tertiary and quaternary carbon atoms. In DEPT , sequence of pulses with various delay time is used to create the DEPT Spectra. Quaternary carbon atom spectra will not be visible in DEPT Spectra. Quaternary carbon atoms are differentiated from primary , secondary & tertiary carbon atom. Sample will be irradiated by electromagnetic radiation of different angle of pulses i.e. 45 degree , 90 degree & 135 degrees. 13 Carbon NMR :- All spectra of carbon will be visible. DEPT 45 gives spectra of primary , secondary and tertiary carbon atoms. DEPT 90 gives Spectra of only CH carbon atom (tertiary carbon atoms). DEPT 135 positive (upward) gives primary and tertiary carbon atoms. DEPT 135 negative (downward) gives secondary carbon atoms.

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