c13 NMR Concept Discuss and Question Solved

¹³C NMR

Although ¹²C is not observed in NMR,only ¹³C is observed in NMR. ¹³C is 1.1% present in nature.

The relatively low abundance of ¹³C is over come by using single avaraging and Fourier transforms.

¹³C (267.53) has lower gyromateric ratio as compared to ¹H (67.8) which is ¼ of ¹H.

Chemical shift range is 0-200 ‍PPM.

Resonance of ¹³C is 6000 weaker than proton.

Nuclear overhauser Enhancement

When a proton decoupled spectrum is obtained, the intensities of the carbon resonance are enhance. This is known as Nuclear overhauser Enhancement (NOE).

When the Hydrogen nuclei are irradiated, the number of nuclei in the higher energy “spin-opposed” state is increase.

The carbon atom to which these proton are attached adjust their equilibrium distribution to increase the population of carbon atom in the lower energy“ spin – aligned” state due to the interaction of spin dipoles.

This large population of carbon atom in the lower spin state result in a large number of nuclei that can be detected and therefore an increased signal.

MCQ

1. Which is range of ¹³C chemical shift ?

A. 0 -10

B. 0-100

C. 0-150

D. 0-200

Ans. D

2.How many percentage of ¹³C is present in nature ?

A. 1.0

B. 1.2

C. 1.1

D. 0.9

Ans. C

3. Resonance of ¹³C is how many weaker than proton ?

A. 5000

B. 6000

C. 3000

D. 2000

Ans. B

4. When a proton decoupled spectrum is obtained , the intensity of the carbon resonance are enhance it is called as

A. NOE

B. PPM

C. Hz

D.cps

Ans.A

5. When hydrogen nuclei are irradiated, the number of nuclei in the higher energy is ?

A. Spin opposed

B. Spin similar

C. A and B

D. None of this

Ans. A

6. how many percentage of ¹²C is present in nature ?

A. 98 %

B. 90%

C. 92%

D. 91 %

Ans. A

7. ¹³C has gyromateric ratio is

A. 267.53

B. 266

C. 234

D. 231

Ans. A

8. ¹H has gyromateric ratio is

A. 267.53

B. 266

C. 234

D. 245

Ans. A

9. When carbon atom in the lower spin state result in a large number of nuclei that can be detected so in spectra

A. Increase signal

B. Decrease signal

C. A and B

D. None of this

Ans.A

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