4. Acquisition

Time requirement: 20 min

Sample: 5% 2,3-dibromopropionic acid in [D₆]benzene.

Record a standard ¹H NMR spectrum and optimize the spectral width. Change to the 2D mode of the spectrometer software and load the pulse program. You have to set:

td2	2 k data points in F₂
td1	256 data points in F₁
sw2	1.5 ppm
sw1	1.5 ppm
o1	middle of ¹H NMR spectrum
p1, p3	90° ¹H transmitter pulse
p2	180° ¹H transmitter pulse
d1	2 s
d2	constant time interval between the pulses p1 and p3, 214 ms, calculated from the increment for t₁ evolution multiplied by td1
initial value for t₁ evolution	3 μs
increment for t₁ evolution	1/[2·sw1]
decrement for t₁ evolution	1/[2·sw1]
g1, g2, g3	sinusoidal-shaped field gradients, 1 ms duration and ca. 0.1 T/m strength, with gradient loop counters, ring-down delays (50 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient strength ratio alternating between 1 : −1 : 2 and 1 : −1 : −2 in successive t₁ increments (echo/anti-echo)
ds	2
ns	1

5. Processing

Apply zero-filling in F₁ to 512 real data points to obtain a matrix of 1024 × 512 real points. Use exponential windows with lb = 2 Hz in F₂ and lb = 5 Hz in F₁. Apply Fourier transformation corresponding to the echo/anti-echo mode of data acquisition in F₁. Phase correction in both dimensions is necessary.

6. Result

The figure shows the phase-sensitive ct-COSY spectrum obtained on a DRX-400 spectrometer. Note that compared with the spectra of the same compound shown in Experiments 10.5–10.7 there is no spin coupling in the F₁ dimension, the diagonal signals are dispersive in the F₂ dimension, and the cross-peaks have the usual up-and-down pattern known from phase-sensitive COSY.