The
correlated spectroscopy (COSY) experiment is the
simplest of the 2D experiments. It consists of only
two pulses with an incremental delay (t1) between
them. The COSY provides information on homonuclear
spins that are coupled to each other, thereby
replacing the homonuclear decoupling experiment. A
proton COSY is most common, but a 11Boron
or 19Fluorine COSY can give much
information about chemical structure as well.
In
the COSY experiment, the first pulse creates
magnetization in the transverse plane. During the
evolution period the delay is incremented
systematically to sample the spectra in the other
dimension also. The second pulse mixes the
magnetization between the spins coupled to each
other. The data is saved as an array that is
Fourier transformed, first in one dimension and then
the second. This gives a 2D spectrum where the
diagonal looks like the normal one dimensional
spectrum and the off-diagonal peaks (cross peaks)
give information on the nuclei that are coupled to
each other through a chemical bond.
1D proton spectrum
data acquired and
processed in about 11 seconds
COSY
spectrum
data
acquired and processed in < 5 minutes
As expected,
the methyl and methylene of the ethyl group are coupled.
Likewise, the vinylic methyl is coupled to both vinylic
protons which are, in turn, coupled to one another. No
coupling exists between the ethyl and vinyl resonances.
