The document discusses nuclear magnetic resonance spectroscopy (NMR). It explains that unlike other spectroscopy techniques, NMR resonance signals are dependent on both the external magnetic field strength and radio frequency used, so the exact location of signals can vary between magnets. It introduces the concept of chemical shift as an alternative method to characterize NMR signals, where electronic environments around nuclei cause small differences in resonance frequencies measured in parts per million from a reference compound.

1. NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY
(NMR)
By
Dr. Abdul Tawab (PS)
e-mail: atawab1@yahoo.com
Health Biotechnology Division
National Institute for Biotechnology and Genetic Engineering

8. 1H NMR Integration

11. NMR an example

12. Chemical Shift
Unlike infrared and UV-Visible spectroscopy, where absorption peaks are uniquely located by a
frequency or wavelength, the location of different NMR resonance signals is dependent on both the
external magnetic field strength and the RF frequency.
Since no two magnets will have exactly the same field.
The resonance frequencies will vary accordingly and an alternative method for characterizing and
specifying the location of NMR signals is needed.
This problem is illustrated by the eleven different compounds shown in the diagram. Although the
eleven resonance signals are distinct and well separated, an unambiguous numerical locator cannot be
directly assigned to each.

13. Chemical Shift

14. Chemical Shift

15. Shielding and chemical shift

16. Shielding and chemical shift

17. Shielding and chemical shift

18. Shielding effects

19. Shielding effects

21. NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (NMR)