INEPT-INADEQUATE spectra

FIGURE 30. 29Si—29Si ID INEPT-INADEQUATE spectra top spectrum for 17, J = 108 Hz bottom spectrum for 18, J = 1.2 Hz (no experimental details given). Reproduced by permission of Wiley-VCH from Reference 238... 

Figure 15 (A) A 2D DJM-INEPT-INADEQUATE spectrum of Me-/J-D-xylopyranoside. (B) F, traces...

Figure 18 Section of a H13C INEPT-INADEQUATE spectrum of 5 at natural abundance and 13C-labeled 6. From Ref. 62, reproduced by permission of the American Chemical Society.

Figure 5.76, The proton-delected INEPT-INADEQUATE spectrum of menthol 5.11 (50 mg in CDCI3) recorded at 400 MHz using the optimised 1,1-ADEQUATE sequence of [97], The step-wise tracing of the carbon skeleton of the cyclohexane ring is illustrated in which carbon connectivities are identihed in horizontal traces (alternative routes involving the diastereotopic 3, 4 and 6 partners also exist but, for clarity, are not shown).

FIGURE 3. 53.7-MHz Si- Si 2D-INEPT-INADEQUATE spectrum (a) Tetracycle 5a in CeDe-(b) Tricycle 6 in CDCI3 (40 °C). and projection of the 2D spectrum on the F2 axis (top). Signals connected by solid lines correspond to one-bond interactions ( /) those connected by dotted lines denote long-range couplings ("/). Reproduced by permission of VCH Verlagsgesellschaft from Reference 12... 

The major disadvantage to this experiment is its extremely low sensitivity. An alternative is INEPT-INADEQUATE (sometimes called ADEQUATE), which uses proton observation and pulsed field gradients over pathways such as H-C-C. The resulting spectrum resembles that of 2D INADEQUATE, but can contain peaks only when at least one of the paired carbons has an attached proton. Although such technical refinements ameliorate the problem of sensitivity, this family of experiments has not been widely used. 

MHz frequency as shown. A proton spectrum occurs over a chemical shift range of 10 ppm, which corresponds to 2.5 kHz at 500 MHz. As seen in Figure 3.22, all of the protons in the sample would see 98%-100% of the power of the 500 MHz radiation delivered and all would be excited simultaneously. A pulse programmer is used to control the timing and shape of the RF pulses used to excite the sample. Square wave pulses are commonly used, but multipulse experiments and 2D NMR experiments with other pulse shapes are performed. There are hundreds of pulse sequences and 2D experiments that have been developed, with curious names like attached proton test (APT), DEPT, INEPT, INADEQUATE, COSY, and many more, some of which will be discussed later in the chapter. Each pulse sequence provides specific and unique NMR responses that enable the analyst to sort out the NMR spectrum and deduce the chemical structure of a molecule. 

In 2006, Milosavljevic and co-workers64 reported a study of the complete 4H and 13C NMR assignment of a new triterpenoid saponin, leucantho-side-A (13), from Cephalaria leucantha L. In the course of determining the structure and assigning the spectra, the authors made extensive use of the normal ensemble of 2D NMR experiments in use for the characterization of natural product structures HSQC, HMBC, DQF-COSY, TOCSY, and NOESY. The authors supplemented the aforementioned list of experiments with 2D /-resolved, DINE-(Double INEPT-Edited)-HSQC, and INADEQUATE spectra. The authors made no mention of the use of the connectivity information derived from the 1,1-ADEQUATE spectrum in the assembly of the triterpene nucleus of the molecule but reported extensive tabulations of the 1,1-ADEQUATE correlations that were used to sequence and assign the saccharide resonances of the tri- and di-saccharide sub-units, 14 and 15, respectively, linked to the triterpene nucleus. 

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