2D-INADEQUATE spectrum

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-... 

The second pulse sequence (HCCH) provides detection of 2D-INADEQUATE spectra in the /7/2 planes wiA detection of H in If a particular H chemical shift is selected, the flJ2 plane will contain the INADEQUATE spectrum of the directly boimd and adjoining. atoms. Because the experiments were performed on labeled polymers, the sensitivity was irly high, however, this experiment does not filter resonances of the polymer backbone from the spectrum. Practical aspects of using these pulse sequences are described by Saito et al.(20)... 

There are several methods for creating multiple-quantum coherence. A pulse sequence used for recording 2D-INADEQUATE spectra is given in Figure 5.82. The pulse sequence consists of two similar halves. During... 

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. 

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... 

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. 

Today, a number of one- and two-dimensional NMR experiments are available for the detection of homonuclear Li, Li and Li, Li couplings. Aside from the COSY experiment, the double quantum filtered COSY (COSY-DQF), the TOCSY, and the ID and 2D INADEQUATE experiments [24] have been successfully employed. An attractive feature of all these experiments is their sensitivity for small scalar interactions which give rise to crosspeaks even if line splittings in the corresponding ID spectra are not resolved. This was first demonstrated with COSY experiments for a paramagnetic nickel complex [82] and for quadrupolar nuclei in the case of boron-11 [83]. 

From the spectra, it is clear that the dimer with m/z 216 is a norbornene dimer terminated with a vinyl group (dimer-4, 113.36 and 141.91 ppm). The compound with m/z 244 is a norbornene dimer with an ethyl and a vinyl group at the head (14.11 and 22.18 ppm) and the tail (113.72 and 142.87 ppm) of the molecule (di-mer-5), respectively. Assignments have been made based on analysis of a C 2D-INADEQUATE spectrum and are presented in Fig. 4.18. Both dimers are enchained in the 2,3-fashion consistent with the proposal based on the NMR analysis of the norbornene polymer made with naked nickel . 

For these high-resolution solid state spectra, many techniques analogous to those used in solution NMR can be applied. For exanple, 2D HETCOR experiments have been achieved using several pulse sequences (138). 2D double quantum correlation NMR (equivalent to 2D inadequate in solution and requiring C-labelled spin pairs) has been found to be a good technique to study chain conformations in the sohd state (139). Homonuclear double... 

The structure of terreinol, a new metabolite isolated from Aspergillus terreus, has been confirmed by a 2D INADEQUATE experiment and all /cc couplings have been determined for this molecule. The INADEQUATE technique has been applied to establish the structure of thiophene-substituted sulfinyl monomers and the phytoestrogen trawi-resveratrol, 3,4 5-trihydroxystilbene. Emsley and co-workers have demonstrated experimentally that by using the tranverse dephasing optimised spectroscopy approach refocused INADEQUATE spectra can be recorded on medium-sized molecules at natural abundance in reasonable experimental times. 

Several peaks arising from different pentad and hexad comonomer sequences have been observed n the C-NMR spectrum of stereoregular 1-butene-propylene copolymers. The paper by Aoki and co-workers [54] demonstrated that the analytical method based on the two-dimensional (2D)-INADEQUATE spectrum and the chemical shift calculation via the y-effect is very powerful for the assignment of C-NMR spectra of higher a-olefin copolymers. A stereoregular 1-butene-propylene copolymer is a suitable example because reliable assignments have been proposed by a reaction probability model [55]. 

The rearrangement of the cage hydrocarbon diazo-nium ion [1] in the presence of water could lead to three possible alcohol products [2], [3] and [4]. Only two alcohol products were obtained from this reaction in isolated yields of 38% and 7%. The structures of these two products could only be determined by the 2D INADEQUATE experiment due to the hydrocarbon nature of their structures, and therefore, the lack of any distinguishing details in the proton spectra. Each compound also had the same number of methylene, methine and quaternary carbons, thus precluding the utilization of structure determination by simple ID spectroscopy. 

With recent advances in NMR probe design, sensitivity has become less of a problem and low sensitivity experiments, such as 2D INADEQUATE, are becoming routine. Indeed, the latest generation cryogenic probes allow recording INADEQUATE [32, 33] spectra in as httle as 10-15 mg of sample within just a few hours of measurement time. On the other hand, as discussed above, multi-receiver experiments provide new ways of obtaining more information from a single measurement. 

Chain-tracing techniques for large molecules may use combinations of 2D J spectra, 2D NOE, and exchange correlation maps. A 2D INADEQUATE spectrum identifies sections of the carbon backbone of a molecule since the presence of a pair of double quantum peaks in the spectrum normally indicates a CC bond. An example of the power of 2D methods in spectral assignment and determination of structure is in the application to biopolymers. ... 

The 2D-INADEQUATE experiment is among the most powerful NMR experiments available when it can be used. It provides valuable information about all of the C-C attachments in an unknown structure. When coupled with DEPT spectra, it provides complete stmeture information with the exception of attachment of heteroatoms. Unfortunately, this experiment is not popular in polymer characterization due to its extremely low sensitivity. It requires the detection of spin pairs... 

In order to provide additional evidence for the above resonance assignments, the authors obtained double quantum and relay 2D-NMR spectra. The former experiment is better known as the ID-INADEQUATE experiment commonly performed on When executed on H, the appearance of the spectmm is identical to the INADEQUATE experiment, but does not suffer from poor sensitivity due to the low abundance of two adjoining NMR-active isotopes as it does in the more common... 

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