4. Acquisition

Time requirement: 20 min

Sample: Prepare a mixture of 0.2 ml CDCl₃, 0.2 ml [D₂]dichloromethane and 0.2 ml [D₆]acetone. Add for the second measurement 0.2 ml of a 1:1:1 mixture of normal chloroform, dichloromethane and acetone.

Load standard ¹³C NMR parameters. You have to set:

decoupler attenuation and 90° pulse duration for CPD
td	64 k data points
sw	200 ppm
o1	middle of ¹³C NMR spectrum
o2	middle of ¹H NMR spectrum
p1	30° ¹³C transmitter pulse
d1	1 s
ns	256

First measure the mixture of the deuterated solvents alone and inspect the different multiplets caused by the different number of deuterium atoms (I = 1). Then add the mixture of the undeuterated solvents and repeat the measurement.

5. Processing

Use standard 1D processing as described in Experiment 3.2 with exponential multiplication (lb = 0.3 Hz). For better digital resolution apply zero-filling to 64 k data points.

6. Result

The figures show three expansions of the ¹³C NMR spectrum obtained from the mixture of deuterated and undeuterated solvents on an AMX-500 spectrometer. For acetone one finds in a a septet with ¹J(C,D) = 19.5 Hz and a ¹Δ isotope effect of −758 ppb, for dichloromethane in b a quintet with ¹J(C,D) = 27.5 Hz and an isotope effect ¹Δ of −391 ppb, and finally for chloroform in c a triplet with ¹J(C,D) = 32.4 Hz and an isotope effect ¹Δ of −192 ppb. For the carbonyl atom of acetone (not shown) a ²Δ of +325 ppb can be detected; note the remarkable sign change. The observed shift measured in Hz for the ¹Δ isotope effects is magnetic field dependent; however, the splitting by the coupling to deuterium is not. Therefore the observed overall pattern will change depending on the spectrometer used.