ID INADEQUATE

Fig. 20 ID INADEQUATE spectrum of compound 2 (75 MHz, 50% solution in CDC13, measurement time 20 hours). Note that the multiplets are distorted because they could not be correctly phased...

Table 5 Results from ID INADEQUATE experiment carried out on diester 2 Chemical shift (ppm) Assignment Coupling constants (Hz)...

The principle of multiple selective excitation has been incorporated into a few ID and 2D experiments, the schemes of which are shown below (fig. 1). Depending on the experiment, either a DANTE pulse train (ID TOCSY [2]), frequency selective 180° pulses (ID NOE [3], ID INADEQUATE [4], ID C/H COSY [5] and 2D TOCSY-COSY [6]) or frequency selective 90° pulses (2D HMBC [11]) are applied to selectively perturb and uniquely label selected spins. Besides the DANTE pulse , composed itself of a series of non-selective rectangular pulses, Gaussian-shaped 180° and... 

Fig. 1. Pulse sequences modified for multiple selective excitation. I ID TOCSY, II het-eronuclear ID NOE, III ID INADEQUATE, IVa heteronuclear ID COSY (optimized to detect Jch), IVb heteronuclear ID COSY (optimized to detect "Jch), V 2D TOCSY-COSY, Via 2D HMBC (designed to detect heteronuclear long-range couplings "Jch only), VIh 2D HMBC (extended pulse sequence to detect both heteronuclear long-range "Jch and...

TOPHAT-shaped 90° pulses are used in other cases as the best compromise with respect to the excitation profile, the phase homogeneity and length. Depending on the type of the detected spin-spin interaction - being either scalar or dipolar coupling - each selected spin is initially perturbed only once (ID TOCSY, ID INADEQUATE, ID C/H COSY, 2D TOCSY-COSY and 2D HMBC), or for several times (ID NOE). With each of the selected spins initially perturbed only once the inherently smaller transient NOEs would be detected in the latter case, whereas with the multiple excitation of a selected spin within the NOE build-up period the stronger steady-state NOEs are more or less approximated. 

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. 

FIGURE 1. ID-INADEQUATE spectrum of (SieMeii)2SiMe2 (4) 500 mg silane in 2 ml CgDg, 30 mg Cr(acac)3 added T = 333 K 6400 FIDs accumulated gentle exponential multiplication insert shows the couplings at Si4 in an expanded scale. Reproduced by permission of Elsevier Science from Reference 11... 

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. 

Further developments along similar lines have been reported recently, initially in the context of ID INADEQUATE.16 The proposed pulse sequence (Figure 3) involves linear and bilinear spin rotations and is termed INADEQUATE LBR. 

ID INADEQUATE LBR pulse sequence generates a theoretical sensitivity enhancement of 41% compared to a regular ID INADEQUATE. The same gain is also provided by ID INADEQUATE CR.5 As the latter pulse sequence contains more delays, ID INADEQUATE LBR is more robust when it comes to the mismatch between the set and actual / values. An experimental comparison, based on 11 sucrose signals, of all three ID INADEQUATE pulse sequences... 

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. 

Figure 28 ID INADEQUATE 77Se spectrum of [Re5OsSe8(CN)6]3 with a 4.1-ms fixed evolution period. Expanded spectra contain multiplets centred at —188.6 and —284.0 ppm. From Ref. 87, reproduced by permission of the American Chemical Society.

Figure 13.17. (a) Simulated expansion of signal 4 of the proton-decoupled 13C spectrum of 2-chlorobutane. (b) Simulated ID INADEQUATE spectrum of the same signal. 

Solution The ID INADEQUATE will exhibit a singlet for such a carbon. Since there are no l3C satellites, its signal will not appear in the 2D INADEQUATE spectrum. ... 

ID INADEQUATE (Incredible Natural Abundance Double Quantum Transfer Experiment)... 

Figure 9 (a) S8.88MHz Li NMR spectrum of a mixture of the dimer (Z)) and monomer (M) of ( )-l-lithio-2-(2-lithiophenyl)-l-phenylhex-l-ene (ca 0.3 M in THF/ TMEDA) (b) Li, Li ID INADEQUATE spectnun of the same sample which identifies the signals that belong to the Li, Li AA XX system of the dimer reference 0.1 M LiBr in THF. (Reproduced with permission from ref. [88])... 

The ID INADEQUATE experiment provides a method for measuring coupling... 

Cccc values have been measured for the bicyclic monoterpenes, 3-carene, a-pinene, and camphene by selective ID INADEQUATE, with 13C at natural abundance, but the agreement between experimental data and the results of SCPT-INDO calculations was not satifactory.133... 

Figure5.75. The ID INADEQUATE experiment (b) selects for the carbon-13 satellites in the conventional carbon-13 spectra (a) and provides a means of measuring carbon-carbon coupling constants. Some residual parent resonances from lone C centres remain in (b).

The first step in increasing the signal intensity in INADEQUATE experiments is to implement a polarization transfer step. The INEPT-INADEQUATE experiment [5.162] starts with the INEPT sequence creating antiphase coherence for the sensitive nucleus with a subsequent coherence transfer step before continuing the basic INADEQUATE experiment. In Check it 5 A. 3.2 the INEPT-IN ADEQUATE pulse sequence is created and the results compared with the unrefocused ID INADEQUATE experiment. 

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