Record a normal ¹³C NMR spectrum and optimize the spectral width. Change to the 2D mode of the spectrometer software and load the pulse program for heteronuclear 2D J-resolved spectroscopy. You have to set:

td2: 1 k data points in F, tdl: 64 data points in F, sw2: 175 ppm sw: 250 Hz (half of the width of the largest multiplet) o1: middle of ¹³C NMR spectrum o2: middle of ¹H NMR spectrum p1: 90° ¹³C transmitter pulse p2: 180° ¹³C transmitter pulse dl:2s initial value for ¢; evolution: 3 μs increment for f, evolution: 1/[2-sw1] pre-acquisition delay: as short as possible ds: 2

5. Processing

Apply zero-filling in F, to 256 real data points. Use squared 7/2-shifted sinusoidal windows in both dimensions. Apply complex Fourier transformation corresponding to the N-type signal selection using the quadrature-off mode in F,. Phase correction is not necessary, since the data are processed in magnitude mode. The data can be sym- metrized with respect to the horizontal through the middle of the spectrum.

6. Result

The figure shows the 2D spectrum obtained on an ARX-200 spectrometer; symmetri- zation has been performed. Note that the splittings observed in F| are only half the ac- tual C,H spin coupling constants.

7. Comments

The sequence is, in principle, identical to the spin-echo technique as described in Ex- periment 6.3, but differs in that now the spin-echo delay r= 2d2 in Experiment 6.3 is incremented (r= 1), thus creating the second dimension. At the completion of ¢,, the chemical shift information is refocused. The echo, however, contains the spin-spin coupling information, which evolved during the second half of #,, when the decoupler was switched off. Therefore, these two signal components are separated after 2D Fou- rier transformation and the splittings are half of the actual spin coupling constants.

There are selective variants of this technique (see Exp. 7.10).