This document describes continuous wave (CW) NMR spectroscopy. It explains that CW-NMR uses a fixed magnetic field and varies the frequency coil current to achieve resonance signals. A typical CW spectrometer contains a sample tube spun between the poles of a powerful magnet. Radio frequency is broadcast into the sample while a receiver coil monitors the absorbed energy. By varying the magnetic field or radio frequency, an NMR spectrum is acquired showing signals from different proton types in the sample. While offering routine 1H NMR studies, CW spectroscopy has limitations such as low sensitivity, requirement for concentrated samples, and production of high noise.

1. Presented by
Sidra
MP-CHE-04
The Women University Multan.
CW NMR
SPECTROMETER

2.  Continuous wave NMR uses a fixed magnetic
field and sweeping of frequency by varying
the current in a frequency coil to achieve
resonance absorption signals. CW -NMR
spectrometer finds routine use for 1H NMR
studies at 60 MHz.
Strength of MF
changed s
Constant RF
frequencys

3.  At constant MF, different protons precess at
slightly different frequencies.
 MF is increased to precess all protons.
 Magnetic has two parts
Main magnet
Electromagnetic
poles

5.  A typical CW-spectrometer is shown in the above
diagram. A solution of the sample in a uniform 5
mm glass tube is oriented between the poles of a
powerful magnet, and is spun to average any
magnetic field variations, as well as tube
imperfections. Radio frequency radiation of
appropriate energy is broadcast into the sample
from an antenna coil (colored red).
 A receiver coil surrounds the sample tube, and
emission of absorbed rf energy is monitored by
dedicated electronic devices and a computer. An
nmr spectrum is acquired by varying the magnetic
field over a small range while observing the rf
signal from the sample. An equally effective
technique is to vary the frequency of the rf
radiation while holding the external field constant.

8.  We have an spectrum of phenyl acetate.
 There are 3 type of protons one of ch3 and
2nd of ch2 and 3rd of benzene ring protons.
 Benzene protons are in deshielded area and
they precess in low field area. Recorder scan
it firstly.
 As we increase the MF the different protons
are precess at different fequencies
 In this method all protons are precess
seperately by varing the Mf.

9. Requires greater
time
Less sensivity
Concentrated
sample

10. Limited to HNMR
High noice