Carbon-13 NMR spectroscopy

Question 1

What is property of carbon-13 is exploited resulting in identification of carbon atoms in an organic molecule.

Answer 1

Carbon-13 has an odd number of nucleons(13), resulting in a residual magnetic spin.

Question 2

In carbon-13 NMR what do chemical shifts indicate about the chemical environments of the carbon atoms present?

Answer 2

The presence of an electronegative atom or group causes a significant chemical shift.

Question 3

Why is carbon 13 very useful in NMR compared to other atoms with an odd number of nucleons?

Answer 3

Carbon-13 is sensitive to nuclear shielding and gives a large range of chemical shift values, typically 0-230ppm. With such a large range, unless carbon atoms are present in an identical environment each carbon atom is likely to show a seperate signal.

Question 4

What are the two pieces of important information that carbon-13 NMR gives?

Answer 4

From a carbon-13 NMR spectrum, the most important information is:

• The number of diffirent carbon environments - from the number of peaks.
• The types of carbon environment - from the chemical shifts.

Question 5

What can carbon-13 NMR peaks no show about the compound that protons NMR spectroscopy can?

Answer 5

The size of the peak tells us nothing about the number of carbon atoms responsible.

Question 6

In carbon-13 NMR, what shows the number of carbon environments?

Answer 6

The number of peaks gives the number of diffirent carbon environments.

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