Analysis using C-13 NMR spectroscopy

Question 1

How does C-13 NMR spectroscopy work??

Answer 1

• Carbon 13 makes up 1.1% of all naturally occurring carbon atoms, so these atoms have 13 nucleons which gives it a significant ‘nuclear spin’, allowing it to be detected
• carbon 13 atoms in different environments (positions relative to other atoms in a molecule) have different chemical shifts relative to a compound called TMS, which can be tracked on a scale.

Question 2

Benefits of C-13 NMR

Answer 2

• Fewer peaks to sort out
• Better separation of certain peaks eg benzene
• Never any coupling

Question 3

How do you identify different positional isomers on a absorption graph and using the displayed formula?

Answer 3

• Positional isomers have the same number of carbons, but different numbers of carbon environments. The carbon environments are determined by the atoms surrounding a carbon, and how close each carbon is to each other carbon group AND other functional groups
• if one of the positional isomers has 3 carbon environments and the other one has 2 carbon environments, you can identify on the graph which is which by the number of lines