HEED INEPT

The original HEED-INEPT sequence306,307 that enhances narrow lines is ... 

FIGURE 45. 29Si spectra of HN(SiMe3)2 (at 71.55 MHz, 80% in CgDf, 10 mm sample tube, 2 K data points zero-filled to 8 K) acquired (a) with INEPT (16 transients) (b) the same as (a) after Gaussian multiplication (LB = —1 Hz, GB = 0.7) (c) with DEPT (16 transients) — note the effect of the longer sequence (d) with HEED-INEPT (64 transients, x = 35.7 ms, A = 19.06 ms, T = 0.3 s). Reproduced by permission of Academic Press from Reference 307... 

Figure 9 The HEED INEPT pulse sequence. The delay T is tuned to minimize the appearance of the parent Si resonance, whereas the delays A2 and A3 are set according to the /hx coupling as usual. Dec. = decoupling...

Fig. iL Pulse sequences for pseudo triple-resonance experiments with passive selection of satellites (a) z-filtered 2D-"X, H( "Y) INEPT. (b) -BIRD H,"X( "Y) HMQC. (c) H,"X( "Y) HMQC experiment with biselective excitation pulse (bis) biselective excitation may be achieved with DANTE or P-BIRD sequences, binomial pulses, or shaped pulses. (d) H, X( "Y) HEED-INEPT." ... 

Previously it was necessary to use N labelled samples in order to determine isotope shifts A N(X). By the application HEED extended pulse sequences,it proved possible to determine these parameters for numerous compounds in the natural abundance of (0.37%). Table 11 lists a number of these data and an example for the application of the HEED INEPT pulse sequence is shown in Fig. 9. 

Fig. 6. 59.8 MHz NMR spectrum (HEED-INEPT (acquisition time 3 s, repetition...

Fig. 12. 99.6 MHz Si H and 50.4MHz N[ H NMR spectra (INEPT) of a tricyclic diaminomethylsilane (courtesy of G. Becker and R. Motz) dissolved in CsDe. The N satellites in the Si NMR spectrum (the parent signal is partially suppressed by using the HEED-INEPT pulse sequence) are not symmetric because of the isotope-induced chemical shift A N( Si). The assignment of the satellites is confirmed by the observation of the Si satellite signals in the N NMR spectrum (box). ...

Many eoupling constants 7( Si, N) have been measured either by detection of satellites in Si NMR spectra (see e.g. Figs. 6 and 12), and for this purpose the application of the HEED-INEPT experiment is particularly helpful. It is also possible to detect the Si satellite signals in the NMR spectra even with N at natural abundance (see e.g. Fig. 12). Frequently it is advisable to record the N NMR spectra under conditions typical of the so-called ultra-high resolution since the natural transverse relaxation times T2( N) can be... 

Selective excitation and selective detection have been recently reviewed by the recognized leaders in this field135 who viewed 29Si NMR applications from a broader perspective. In this review we focus on those selective experiments that have found wider use in studies of organosilicon compounds, selective INEPT and HEED as representatives of the two classes (excitation and detection) of selective experiments. Some other selective experiments are mentioned in other sections (e.g. SPT, selective decoupling, SPINEPTR, V>-BIRD HMQC, DQF COSY). 

Figure 6 111.9MHz Sn NMR spectrum of l,l-dimethyl-2,2-bis-(trimcthyl-stannyl)hydrazine (2S°C 2S% in C () recorded by the refocused INEPT pulse sequence with H decoupling and Hahn-echo (HEED) extension [20] (Hahn-echo delay 0.16 s), showing the reduced intensity of the parent line, allowing the straightforward assignment of the N satellites (marked by asterisks /(" Sn, N)=4S.SHz) and the measurement of the isotope induced shift A / N(" Sn) = —0.0365 ppm...

Bis(diphenylphorpanyl)amine - application of the INEPT-HEED pulse sequence. Wrackmeyer and co-workers communicated the results of a study of measure-... 

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