initial value for ¢, evolution: 3 μs increment for ¢, evolution: 1/[2-sw1]

5. Processing

Apply zero-filling in F, to | k real data points to obtain a symmetrical matrix of 1024x1024 real points. Use Gaussian windows in both dimensions. Apply real Fourier transformation corresponding to the TPPI mode of data acquisition in F,. Phase cortection for phase-sensitive COSY spectra can be performed in two ways. If one has measured a 1D ¹H NMR spectrum under the same conditions as for the 2D file (same probe-head tuning, same spectral width, time domain, and pre-acquisition delay) one can phase the 1D spectrum and use the phase correction parameters in the F, dimen- sion of the 2D file. Otherwise, using the 2D phase correction routines of the NMR software, one adjusts strong diagonal peaks at the left and right of the spectrum in dis- persion, which yields the cross-signals in pure antiphase.

6. Result

The figure shows an expansion of the phase-sensitive COSY spectrum obtained on an AC-300 spectrometer for the two cross-peaks connecting H-3b with H-2, and H-3b with H-3a. The dotted contour lines represent negative signals, the solid contour lines positive signals. In this type of COSY spectrum the active coupling (the one that causes the cross-peak) is in antiphase, whereas the passive one remains in-phase. Thus from the cross-peak at 5); = 3.85 it can be seen that J(H-3b,H-2) is small (4.6 Hz), whereas J(H-3b,H-3a) is larger (-10.1 Hz). The cross-peak at 5 = 3.35 displays the active coupling J(H-3b,H-3a) and the passive coupling J(H-3a,H-2) = 11.0 Hz. For the sign determination see Experiments 4.6 and 10.6.

7. Comments

The TPPI (time proportional phase increment) method in 2D somewhat resembles the sequential quadrature detection of 1D spectra. Thus, for each f, increment the phase of the first pulse is incremented by 90°, leading to sine, cosine, –sine, –cosine character of the corresponding FIDs. For the same resolution, twice the number of FIDs have to be recorded compared with the standard COSY. In the RSH (Ruben-States–Haber-