L4 - C-13 NMR Spectroscopy

objectives

• investigate the processes used to analyse the structure of simple organic compounds addressed in the course, including but not limited to:
  • carbon-13 NMR

WHAT IS NMR AND WHAT DOES AN NMR SPECTRUM TELL YOU?

• Proton nuclear magnetic resonance spectroscopy provides...
• information about the Carbon atoms in molecules

How does it work?

• involves the interaction of materials with the LOW ENERGY RADIO WAVES

It provides the information by...

• spinning a sample of the compound in a magnetic field
• Carbon atoms in different environments respond differently to the field
• each different environment of carbon produces a signal in a different position

Origins of NMR Spectra

All nuclei possess charge and mass. Those with either an odd mass number or an odd atomic number also possess spin. This means they have angular momentum.

Information on Spectra

NMR spectra provide information about the structure of organic molecules from the ...

• number of different signals in the spectrum
• position of the signals (chemical shift)
• intensity of the signals

C-13 NMR Spectroscopy

After hydrogen, the most useful atom providing information is carbon-13.

Natural carbon contains about 1% of this isotope so the instruments for its detection need to be sensitive and spectra will take longer to record.

Only the chemical shift is important as each spectrum gives only single lines for each chemically equivalent carbon.