INADEQUATE spectrum

The lower signal is more complicated, and before we can interpret it exactly we need some background information. The magnitude of one-bond C-C coupling constants depends on bond hybridization (ethane 35, ethene 68, benzene 56, ethyne 172 Hz), while two- and three-bond C-C couplings are very small, often around 2-5 Hz. The second thing we have to remember, and this is a new concept, is that the lines in the multiplets from INADEQUATE spectra often come from different spin systems ... 

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. 

Retrorsine (22) was recently used as a model compound in a study of carbon-carbon correlations observed in 1,1-ADEQUATE and INADEQUATE spectra. It was noted by Martin and co-workers51 that modulations of 1Jcc correlations between pairs of sp2 carbons and from an sp3 carbon to an sp2 carbon can lead to gaps in the connectivity network being determined for adjacent carbons (see Figures 7 and 8 and also Section 3.4). In addition to the investigation of the 1,1-ADEQUATE correlations of the... 

F7g. 2.49. INADEQUATE spectra of the 13C—UC doublets of piperidine (neat liquid. 50 MHz), including an analysis of one-, two-and three-bond carbon-carbon coupling constants [58]. 

The chemical shifts and the 29Si-29Si coupling constants (determined from the ID-INADEQUATE spectra) are summarized in Table 1. Figure 1 shows the ID-INADEQUATE spectrum of 4. If all the 29Si-29Si couplings can be determined, the structure of the compound can be easily derived. 

Identify the compound C8H9N02 from its H, 13C/DEPT, COSY, HMQC, and INADEQUATE spectra and show all correlations. 

FIGURE 28. 29Si—29Si INADEQUATE spectra of [Me3Si)2SiMeSiMe2]3SiMe. Top ID spectmm (r = 4.1 ms, A = 3 ps) bottom 2D spectrum (t = 4.1 ms). Reprinted from Reference 223. Copyright 1998, with permission from Elsevier Science... 

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... 

Crowded ID INADEQUATE spectra can be simplified by utilizing the editing properties of INEPT or DEPT249 in their combination with the INADEQUATE or by application of spectral editing as described for the 13C—13C SEMINA pulse sequence (,S MUT editing of IN AI )EQU ATE)249,250 or an INADEQUATE-SEFT combination251. 

It should be noted that single-transition INADEQUATE spectra are generally not suitable for the determination of coupling constants. This is because the readout of the couplings in F2 is affected by the isotope shifts. The combined use of F2 and F1 dimensions, which yields, in principle, the values of coupling constants, is problematic due to limited digital resolution in F A possible solution is to acquire two spectra with the selection of one transition at the time. This should still be a factor of V2 more sensitive compared to regular INADEQUATE on an equal time basis.5... 

Most of the carbon-carbon coupling constants published recently have been measured using 2D 13C-detected INADEQUATE spectra.39-44 ID INADEQUATE experiments were used less frequently43 45 due to potential overlap problems. The measured coupling constants are usually used to resolve stereochemical problems and also compared with theoretical values. 

Frequency separation between the two lines of AP doublets in 13C-detected INADEQUATE spectra corresponds to 1/cc coupling constants, which are simply read out from the spectra. However, accurate determination of njcc coupling constants is more problematic due to possible partial cancellation of closely spaced AP doublets. The peak-to-peak distance in such doublets does not correspond to actual value of the coupling constant. A solution to this problem was proposed recently in the form of IPAP-INADEQUATE experiment (Figure 9) 32... 

Figure 14 Determination of interglycosidic coupling constants of Me-/ -D-lactoside, shown in the inset, using F1 traces from IPAP DEPT-INADEQUATE spectra. The long-dashed lines are the sum or the difference of the in-phase (solid line) and anti-phase doublets (short-dashed line).

A recent study of brominated pyrrole-imidazole alkaloids8 illustrates the usefulness of additional carbon-carbon connectivities provided by 1,1-and INADEQUATE spectra when analysed in conjunction with a 1H-13C HMBC experiment. 1,1-ADEQUATE allows the distinction to be made between the 2/ch- and 3 4/cH-mediated correlations seen in the HMBC spectrum, while the INADEQUATE extends the 1H-13C HMBC correlations by another carbon atom, effectively providing pseudo-4 5/cH correlations. This is illustrated in Figure 17 using monobromophakellin (4). The ADEQUATE experiments required ca 20 h in total of the acquisition time using 21 mg of 4 on a 600-MHz NMR instrument equipped with a BRUKER TCI cryoprobe. 

The capabilities of the Nano-probe were challenged in a completely different fashion in 1996 by a study reporting the characterization of novel steroids from Trichilia hirta through the acquisition of INADEQUATE spectra.192 Using samples of 11 and 9 mg, respectively, INADEQUATE spectra were recorded to establish the structures of 99 and 100. Data were acquired in 62 h for each sample and the interpretation of the data was facilitated through the use of FRED software.84 86... 

Carbon-13 spectra are inherently less complex than proton spectra fortw reasons, viz. (a) chemical shifts between l3C nuclei in different chemical environments can differ by as much as 200 ppm whereas proton shift diflleh ences are seldom more than 10ppm (b) as the natural isotopic abundant of, 3C is only 1.1%, coupling between t3C nuclei themselves is not obsenaf. (but see 2-D INADEQUATE spectra, p. 418). 

Polymers with very low light transmission properties give highly inadequate spectra, which are difficult to evaluate. The lower curve in Fig. 5.1-14, for instance, shows the spectrum of polyethylene, including 2% soot. The upper portion of Fig. 5.1-14 shows that the scale expansion considerably enhances the accessible information content of the spectrum (Peitscher, 1979). 

Asakura, T. Nakayama, N. Demura, M. Asano, A. Carbon-13 NMR spectral assignments of regioirregular polypropylene determined from two-dimensional INADEQUATE spectra and chemical shift calculations. Macromolecules 1992, 25, 4876-4881. 

D INADEQUATE spectra have been used to establish the structure of a series of P-propiothiolactones, of a series of precursor polymers towards poly(p-phenylene vinylene), of l,16-di(2-carbomethoxy-2-propyl)-l,16-dihy-dro[60]fullerene and of the fullerene anion. One-bond carbon-... 

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