TOCSY spectrum of codeine
TOCSY (Total Correlation Spectroscopy) is similar to COSY, in that it maps out which Hs are coupled to each other, but in a TOCSY spectrum, correlations are seen between all Hs in a spin system, not just those directly coupled to each other.
For example, consider 3-heptanone:
Protons a, b, c and d constitute one spin system, an unbroken network of coupled protons. The ethyl group, e and f, constitutes a second, separate spin system, because there is no coupling between a and e, across the carbonyl.
In a COSY spectrum, CH2 a would show a correlation to CH2 b. In a TOCSY spectrum, it would also show correlations to CH2s c and d.
Codeine (3.3 mg in .65 ml CDCl3)
The TOCSY spectrum of codeine is shown below. As with all homonuclear 2D plots, the diagonal (lower left corner to upper right corner) consists of intense peaks that match the normal spectrum, as do projections onto each axis. The interesting information is contained in the "cross-peaks", which appear at the coordinates of 2 protons which belong to the same spin system.
The cross-peaks marked with red and green circles are longer-range correlations, not observed in the COSY spectrum. The green circles mark cross-peaks to the water peak. Water in the solvent exchanges with the OH of codeine, which is coupled to H-10, which is, in turn, coupled to H-9.
It takes time for the longer-range correlations to develop (referred to as magnetization transfer), so the final spectrum is dependent on delay values in the pulse sequence. In practice, several spectra may be acquired using different delay values. The intensity of each cross-peak will vary through the series of spectra – long range correlations will "grow in" as the delay value is increased, and shorter range couplings may disappear.
Table of TOCSY peaks:
512 complex points in the direct dimension
128 t1 increments
mixing time 70 ms
2 sec relaxation delay
Total time: ~20 min.
sine squared window function (0 degree phase shift) in both dimensions
2x zero-fill in the indirect dimension
magnitude calculation (no phasing needed)
final size 512 x 512
See processing details.
Last updated: 01/22/2003