4. Acquisition

Time requirement: 1 h

Sample: 90% 1-hexanol in [D₆]acetone.

Tune the probe-head to the actual sample and record a normal ¹³C NMR spectrum with ¹H broad-band decoupling. Optimize the spectral width and determine the 90° and 180° pulse lengths (see Exp. 2.2) for this sample. Load the pulse program and set the following parameters:

decoupler attenuation and 90° pulse for CPD
td	32 k
sw	60 ppm (spectral range for C₆H₁₃OH)
o1	40 ppm above TMS frequency (middle of that range)
o2	middle of ¹H NMR spectrum
p1, p3, p4	90° ¹³C transmitter pulse
p2	180° ¹³C transmitter pulse
d1	3 s
d2	1/[4¹J(C,C)] = 7.6 ms, calculated from ¹J(C,C) = 33 Hz
d3	3 μs
ds	4
ns	512

5. Processing

Use standard 1D processing as described in Experiment 3.2; apply zero-filling to 64 k, use exponential multiplication with lb = 0.5 Hz.

6. Result

The figure shows the ¹³C 1D-INADEQUATE spectrum of 1-hexanol obtained on an ARX-300 spectrometer using a 5 mm ¹H/¹³C dual probe-head. Note the remarkable suppression of the singlets of the mono-¹³C isotopomers. Closer inspection of the observed splittings (see expansion) shows that some couplings are obviously equal. For instance, the signal at δ_C = 32.4 (C-4) is just one doublet so that an unequivocal assignment based solely on the ¹J(C,C) values is not possible. Furthermore, doublets may show a “roof effect”, characteristic of AB systems (see signal at δ_C = 33.2). The problem of assignment may be overcome by using the 2D version (see Exp. 10.23) in which the various AB spectra are spread out into the second dimension of double quantum frequencies or by using SELINQUATE (Exp. 7.7). As an exercise you may measure the 1D-INADEQUATE spectrum of 2-cyclohexene-1-one, where all C,C couplings are different and clearly resolved. Compare the result with that of Experiment 7.7.