2D exchange spectrum

The principle of detailed balance (and the micro reversibility) [48] requires that 2D exchange spectrum A Tm) is always symmetric. The matrix A(0) represents a 2D exchange spectrum recorded at = 0. It is a diagonal... 

Fig. 42 Contour plot of a 2D exchange spectrum of phenyl deuterated BPA-PC at - 40 °C, with tm = 500 ms (from [38])...

Texch- The relation between this A and the 2D exchange spectrum S is given by... 

D exchange spectrum, two nuclei are very close to each other in... 

As an example. Fig. 3.2,7 depicts H-2D spectra of polypropylene obtained in this way [Sch2]. Signals are identified which spread over the 2D frequency plane. These signals characterize the reorientation of the molecules during the mixing time tm Because detailed balance requires that frequency components are exchanged by reorientation, this type of 2D spectrum is referred to as a 2D exchange spectrum. 

Fig. 9. Top H-2D exchange spectrum of dimethylsulfone. The inset shows the corresponding theoretical spectrum for a two-site jump with a jump angle of 106°. The angular information is encoded in the shape of the elliptical ridges perpendicular to the main-diagonal spectrum. Bottom Theoretical ridge pattern (contour plots) for different jump angles. (Adapted with permission from Refs. 138,140.)...

Fig. 7.27. (a) Schematic visualization of chain diffusion in polyethylene, (b) 2D exchange spectrum of UHMWPE. a and c indicate peaks for the amorphous and the crystalline phases. Peaks of ac or ca arise from the chain diffusion between the crystalline and amorphous phases [37]. 

Figure 13.20. Contour plot of the 2D exchange spectrum of compound 10-18. (Contributed by Alan Sopchik of Wes Bentrude s group at the University of Utah.)...

One can now perform pulsed two-dimensional (2D) EPR spectroscopy completely in the time domain. - As a final example, Fig. 8 shows a 2D exchange spectrum of a spin-labeled peptide, using the pulse sequence tr/2-ti-tr/2-T-7r/2-t2, where T is the mixing time. During T the magnetization is stored parallel to Hq, and exchange between hyperfine lines can... 

Figure 5. a, 2D exchange spectrum of heptamethylbenzenonium ion in 9.4 M HiSOi obtained by a 2D Fourier transformation from 64 free induction decays with t/ values ranging from 0 to 142 ms, and with = 280 ms (60-MHz proton resonance on a modified Varian DA60 spectrometer, 40°C sample temperature), b. Contour plot based on the same data as used for Figure 5a. Off-diagonal peaks indicate slow intramolecular exchange between the four nonequivalent groups of protons labeled 1 to 4. (Reproduced, with permission, from Ref. 26. Copyright 1979, American Institute of Physics.)...

Figure 6. The 2D exchange spectrum of the 50 50 mixture of methyl silsesquioxane and LI01 obtained with a 0.25 s mixing time. The solvent lines are marked (s).

There is a growing realization of the power of the technique in the catalysis area, especially when combined with the use of modern multipulse procedures such as distortionless enhancement by polarization transfer (DEPT), 2D tritium/proton correlation, 2D /-resolved NOE difference spectroscopy (NOESY), and 2D exchange spectrum (EXSY). Thus, in the... 

Figure 6. Analysis of molecular motions of the columnar phase of a tetrabenzocyclophane derivative by 2D exchange NMR. Top molecular structure and schematic diagram of the motion. The first sofa con-former is converted by pseudorotation into a second sofa conformer, this first step being followed by a proper rotation of the molecule. Bottom left deuter-on 2D exchange spectrum of the phenyl-ring deuter-ated compound showing the ridge pattern characteristic of 90 jumps. Bottom right stacking of the molecules in a column. For details see [97].

Figure 5.72. 2D-Exchange spectrum for the keto-enol tautomerism of acetylacetone measured by NOESY. The upper spectrum was obtained at 40° C while the lower one was recorded at 28 °C. The broad signal corresponds to the water protons. The cross lines represent directly connected protons.

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