Contour plots correlation spectrum

The pulse sequence which is used to record CH COSY Involves the H- C polarisation transfer which is the basis of the DEPT sequence and which Increases the sensitivity by a factor of up to four. Consequently, a CH COSY experiment does not require any more sample than a H broadband decoupled C NMR spectrum. The result is a two-dimensional CH correlation, in which the C shift is mapped on to the abscissa and the H shift is mapped on to the ordinate (or vice versa). The C and //shifts of the //and C nuclei which are bonded to one another are read as coordinates of the cross signal as shown in the CH COSY stacked plot (Fig. 2.14b) and the associated contour plots of the a-plnene (Fig. 2.14a and c). To evaluate them, one need only read off the coordinates of the correlation signals. In Fig. 2.14c, for example, the protons with shifts Sh= 1.16 (proton A) and 2.34 (proton B of an AB system) are bonded to the C atom at c = 31.5. Formula 1 shows all of the C//connectivities (C//bonds) of a-pinene which can be read from Fig. 2.14. 

Figure 14. Contour plot of the 360 MHz H-NMR correlation spectrum of dl-camphor. A 64 x256 data set was accumulated with quadrature phase detection in both dimensions and the data set was zero filled once in the dimension and symmetrized. T was 5 sec and t was incremented by 1.63 msec. Total accumulation time was 24 minutes and data workup and plotting took 15 min.

Figures 13.7 and 13.8 are two examples of two-dimensional NMR spectroscopy applied to polymers. Figure 13.7 is the proton homonuclear correlated spectroscopy (COSY) contour plot of Allied 8207A poly(amide) 6 [29]. In this experiment, the normal NMR spectrum is along the diagonal. Whenever a cross peak occurs, it is indicative of protons that are three bonds apart. Consequently, the backbone methylenes of this particular polymer can be traced through their J-coupling. Figure 13.8 is the proton-carbon correlated (HETCOR) contour plot of Nylon 6 [29]. This experiment permits the mapping of the proton resonances into the carbon-13 resonances.

FIGURE 23. Contour plots of the 2D H-29Si correlation experiments on silica gel obtained with a 22.0 ms contact time, a 3.0 s repetition time and a 4.0 kHz sample spinning rate. The vertical axis represents the proton chemical-shift scale and the horizontal axis the 29Si chemical-shift scale. The spectra above and at the side of the figures are the one-dimensional projections. The 2D spectrum was obtained from 64 individual experiments (a) unwashed silica gel, 80 scans for each individual experiment (b) D2O washed sample, 200 scans for each experiment. Reprinted with permission from Reference 137. Copyright 1988 American Chemical Society... 

The functions, and ij/, are called the synchronous and asynchronous 2D intensity correlation functions, respectively. These functions represent the overall similarity and dissimilarity, respectively, between two intensity variations at vi and V2 caused by changing the magnitude of the perturbation. The results are plotted on two orthogonal axes (vi and V2) with the spectral intensity plotted on the third axis normal to the 2D spectral plane. Figures 3-31A and 3-3 IB illustrate schematic contour maps of a synchronous and an asynchronous 2D correlation spectrum, respectively, where + and - signs indicate the directions of the contour peaks relative to the 2D spectral plane. 

Several of the spectra in this workbook were obtained using techniques such as proton-detected C-H shift correlation and multiple-quantum-filtered phase-sensitive COSY which were not covered in detail in our main text because they have come into general use since it was written. This is a measure of the rate at which practical NMR is progressing but presents no problem in the interpretation of the spectra. Various field strengths and modes of presentation, ranging from continuous-wave traces to phase-sensitive two-dimensional contour plots, were used for the spectra. In part, this reflects the history of individual problems, but it is also intentional. It is important to be able to extract the essential message of a spectrum independently of the way it is presented. 

The simulated double-quantum coherence 2D INADEQUATE spectrum of 2-chlorobutane is shown in Figure 13.18. The normal 13C spectrum is plotted along the top. Only the cross peaks appear in the contour plot, and each cross peak appears as a doublet (a pair of dots) at this level of resolution. The separation between these dots, about 35 Hz in this case, is /Cc- Each pair of correlated (by one-bond coupling) cross peaks is indicated by a separate dotted horizontal line, with the midpoint of each line on the diagonal. The F axis is the double-quantum frequency, essentially the sum of the 8v values of the two coupled nuclei. 

The relevant part of the 2D 13C exchange spectrum of this molecule (at -90°C in toluene-d8) is shown in the contour plot of Figure 13.20. Note how the symmetrically placed cross peaks indicate that the signals at 5 52.1 and 56.15 are correlated by exchange at -90°C, even though this exchange is not apparent in the ID spectrum until the temperature is raised much higher. 

Fig. 5. HMQC spectrum of a 0.55 pmol sample of cryptolepine (1) dissolved in 30 pL d6-DMSO. The data were acquired in a 25.5 h experiment using a 1.7 mm gradient triple resonance submicro-NMR probe at 600 MHz. The minor correlation responses in the spectrum designated by arrows are an 8% ( 12pg) impurity of cryptolepine A-oxide present in the sample. All of the impurity responses were visible in a 12 h contour plot. Full HMBC data consistent with the structure were acquired for the impurity in 55 h. (Reprinted with permission from Ref. 12. Copyright 1998, American Chemical Society and American Society of Pharmacognosy.)...

Since the C NMR spectrum of the unknown compound is not more congested than its H spectrum, HMBC is the experiment of choice to establish the longer range C-H correlation networks. Standard and gradient HMBC spectra of the 15-mg sample of the unknown compound are shown in Figure 7-18, and the data from these contour plots are summarized in Table 8-4. 

Figure 2.1.3 Contour plot of the 2D 500.1 MHz H detected H/ Sn shift correlation (HSQC) of a sample of a reaction mixture containing three different tin-boron compounds. The mixture could not be analyzed by direct Sn NMR methods. (Adapted from Reference 152.) The f, projection shows the Sn NMR spectrum with its broad lines as a result of Sn,"B) 1000 Hz. The overlapping Sn resonances are well resolved in the contour plot, and the unstable species Me3SnB(OMe)2 (marked by lines towards f, and F2) can be readily identified. The insert shows the influence of relatively slow B quadrupolar relaxation in [Me3SnBH I giving rise to fairly sharp Sn NMR signals. (Reproduced from Reference 204, with permission form Wiley-VCH.)...

CH COSY experiment does not require any more sample than a H broadband decoupled C NMR spectrum. The result is a two-dimensional CH correlation, in which the shift is mapped on to the abscissa and the H shift is mapped on to the ordinate (or vice versa). The and //shifts of the // and nuclei which are bonded to one another are read as coordinates of the cross signal as shown in the CH COSY stacked plot (Fig. 2.14c) and the associated contour plots of the a-pinene (Fig. 2.14b and c). To... 

Figure 27. Lower, three-dimensional presentation of the spectral region, 0.5-6.0 ppm of a 360 MHz spin-echo-correlated H-NMR spectrum of BPTI. The chemical shift, 5, on the horizontal axis corresponds to that in conventional, one-dimensional spectra. Ad on the vertical axis stands for the difference frequencies between correlated nuclei. Cross-peaks between J-coupled nuclei are at 0.5 Ad. The solvent singlet resonance is at 4.35 ppm. Upper, contour plot of the same spin-echo-correlated spectrum of the inhibitor.

The contour plot in Fig. 11 shows large peaks for the acetate methyl protons and, at the same carbon shifts 170.7 and 171.3), peaks for 6-H2 of the glucose and 2-H of the fructose unit (identified by prior assignment of the spectrum). The other three carbonyls (Sq 171.5, 171.9, and 172.6) belong to 3-methyIvalerates and show correlations to 4-, 3-, and 2-H, respectively, of the glucose unit. Hence structure 12 was deduced. 

Figure 5.14 Schematic representation (right) of the Jcc-edited HSQC-1,n-ADEQUATE spectrum that can be calculated from an inverted Jcc 1,n-ADEQUATE and unedited HSQC spectrum via covariance processing. The four types of correlations possible are shown in the legend beneath the schematic of the contour plot. Parenthetic information indicates correlations between pairs of protonated carbons (CH-CH) or between a protonated and non-protonated carbon (CH-C) via either Jcc or "Jqc coupling pathways designated of the structure on the left. Reprinted with permission from Martin et al. [31]. Copyright 2012 John Wiley Sons, Ltd.

There are many different ways to plot a 2D IR correlation spectrum. A pseudo-three-dimensional representation (so-called fishnet plot) as shown in Figure 1-1 is well suited for providing the overall features of a 2D IR spectrum. Usually, however, 2D IR spectra are more conveniently displayed as contour maps to indicate clearly the location and intensity of peaks on a given spectral plane. In the following section, basic properties of and information extracted from 2D IR spectra are reviewed by using schematic contour maps (Figures 1-10 and 1-11). 

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