CIGAR-HMBC spectra

Fig. 18. H4/C3 JcH response in three CIGAR-HMBC spectra of 2-pentanone showing the effect of varying the parameter /scale- The response shown in Panel (a) was acquired with /s -iie = 0. As expected, no skew is observed in F. When is increased to 6, a modest degree of skew is introduced as shown in Panel (b). Finally, when /scale = 24, a considerable degree of F skew is introduced. In practice, we have found it useful in the author s laboratory to use /scale = 15 to afford an adequate degree of F skew for long-range response authentication.

One of the examples shown by Kline and Cheatham compares the correlations observed in a GNHMBC experiment with those from a N-optimized CIGAR-HMBC experiment performed on 5-chloro-l,3-dimethylpyrazole (2). When conventional, statically optimized GNHMBC data were acquired, then only a correlation from the H4 resonance to the NMe N1 resonance at 196.7 ppm was observed. In contrast, when a 3-10 Hz optimized CIGAR-HMBC spectrum was recorded, a correlation was also observed to the N2 resonance at 309.5 ppm. 

To simulate the 2D [13C, 1H] CIGAR-HMBC spectrum for the spin system used in the Check its 5.S.2.3 and 5.5.2A, load the file ch5525.cfg. Process the data in 2D WIN-NMR. To examine the signal modulation in f1 by the 1H- >H coupling, run a series of simulations using different values of id23 starting with the current Jscale value of 8 [Hz]. 

Figure 20 Timing diagram of the suggested 2y,3y-HMBC experiment, including a LPJF3 for efficient 1JCH suppression. The sequence is virtually identical to the CIGAR-HMBC pulse sequence. The STAR operator is also a constant-time variable element. In this fashion, scalable F, modulation can be specifically introduced for 2JCH cross-peaks into the spectrum independently of the digitization employed in the second frequency domain.

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