Antiphase peaks

Although this is strictly an NOE experiment, we see strong/-coupling artifacts. Selection of Hj, for example, gives a strong antiphase peak at the Hi resonance due to the vicinal H6-H7 coupling in the olehn functional group. This zero-quantum artifact comes from... 

As mentioned already, the INEPT spectra are typified by the antiphase character of the individual multiplets. The INEPT C-NMR spectrum of 1,2-dibromobutane is shown, along with the normal off-resonance C-NMR spectrum, in Fig. 2.12. Doublets show one peak with positive phase and the other with negative phase. Triplets show the outer two peaks with positive and negative amplitudes and the central peak with a weak positive amplitude. Quartets have the first two peaks with positive amplitudes and the remaining two peaks with negative amplitudes. 

Figure 5.30 Drawing of a spectrum with cross-peak at v., Vx in an AMX system. The active couplings display an antiphase disposition of peaks. If we read horizontally./xx is active and /xm passive if we read vertically, is active and Jmx passive.

Since many of the signals in COSY spectra are in antiphase, they may not show up as cross-peaks due to the intrinsic nature of the polarization transfer experiment. The intensities of cross-peaks in COSY spectra may be represented by an antiphase triangle (Fig. 5.33B), in contrast to multiplet... 

One problem associated with COSY spectra is the dispersive character of the diagonal peaks, which can obliterate the cross-peaks lying near the diagonal. Moreover, if the multiplets are resolved incompletely in the crosspeaks, then because of their alternating phases an overlap can weaken their intensity or even cause them to disappear. In double-quantum filtered COSY spectra, both the diagonal and the cross-peaks possess antiphase character, so they can be phased simultaneously to produce pure 2D absorption line... 

The last 90° pulse on 13C acts as a purge pulse for the undesired dispersive magnetization.47,48 The function of the pulse is to convert any magnetization remaining antiphase with respect to the 13C spin into unobservable multiple-quantum coherence. This will provide cross peaks with pure lineshapes and with higher resolution, and consequently establishes reliable determination of coupling constants.47,48... 

The antiphase and in-phase data sets are shown in (a) and (b). In (c), two subspectra are overlaid (indicated as solid and dashed line contours) and the corresponding intra- and interresidual connectivities can be distinguished by the 53 Hz offset of a and p states of the sequential cross peaks, whereas the intraresidual cross peaks... 

Fig. 21. Schematic illustration of MP-HNCA-TROSY antiphase (a) and in-phase (b) spectra with long acquisition time in q. The corresponding subspectra are shown after addition of the antiphase and in-phase data sets (c) and after subtraction of the antiphase and in-phase data sets (d). Due to very small Vcc > the intraresidual cross peaks are almost entirely cancelled out from the antiphase spectrum (a). In the subspectra, the intraresidual cross peaks are shown as doublets, separated by 53 Hz splitting in Fi-dimension, whereas sequential cross peaks are shown as singlets, and they exhibit 53 Hz offset for the upheld and downfield components between the subspectra.

I h. correct values of coupling constants were attributed to the appropriate protons by the analysis of antiphase structures of cross-peaks in DQF-COSY spectrum. 

From LEED measurements of H monolayers adsorbed on Fe(110) Imbihl et al. proposed a phase diagram as shown in Fig. IS. In addition to lattice gas and lattice fluid phases, two commensurate ordered phases were identifled, denoted as (2 x 1) and (3 x 1) in the figure (cf. Fig. 16). The shaded regions are interpreted as incommensurate phases or as phases composed of antiphase domains their signature is that the LEED spot does not occur at the Bragg position but rather the peak is splitted and satellites appear (Fig. 17). 

The purpose of the C(o i)-half-filter is to start the TOCSY experiment only with the magnetization of protons bound to C. No further C pulses are applied after the start of the evolution time t. For the description of the multiplet fine-structure of the resulting cross-peaks, it is instructive to consider a 3-spin system with the operators H, and C denoting the spins of two protons and one carbon. Starting from antiphase magnetiza-... 

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