Figure 9.44
Schematic COSY spectrum of a two coupled spins, denoted
A and X. For convenience, the normal one-dimensional
spectrum is plotted alongside the F 1 and F 2 axes and the^
diagonal (F 1 = F 2 ) is indicated by a dashed line. This^
spectrum shows two types of multiplets: those centred at
the same F 1 and F 2 frequencies, called diagonal-peak^
multiplets, and those centred at different frequencies in the
two dimensions, called cross-peak multiplets. Each multiplet
has four component peaks. The appearance of a
cross-peaked multiplet centred at F 1 = δA, F 2 = δx indicates^
that the proton with shift δA is coupled to the proton^
with shift δA. This observation is all that is required to^
interpret a COSY spectrum.multiplet, or arrays of peaks, are observed, viz. those centred on the diagonal F 1 = F 2 and those where F 1
≠ F 2 which are termed cross-peak multiplets. The diagonal-peak multiplets are of no direct interest
other than correlating them with both the 1-D spectra plotted alongside. However, the fact that
horizontal and vertical lines (not shown) drawn from each cross-peak intersect the diagonal line at the
positions of the diagonal peaks confirms that protons A and X are indeed coupled to each other. It
should be noted that for each pair of coupled protons or groups of protons the cross-peaks always occur
in pairs, equidistant on either side of the diagonal, and that the overall pattern is symmetrical.
Furthermore, the coordinates of the centre of each cross-peak are the frequencies (chemical shifts) of
the A proton and the X proton measured along the F 2 and F 1 axes respectively. These multiplets arise
because of 'mixing' of the signals derived from the coupled nuclei during the evolution period of the
pulse sequence.
Figure 9.45 shows a labelled COSY spectrum of geraniol where confirmation of the^1 H–^1 H connectivity
(coupling) between protons 5 and 6 has been shown by the dotted lines. Other connectivities can be
confirmed in the same way.