Coupling structures

For those purposes, the authors used constant-time version of the sensitivity-enhanced HMBC sequence,79 combined with a two-step low-pass J filter. Constant-time experiments have no coupling structures in the carbon dimension making it easy to identify the centre of signals in... 

Figure 34 Excerpts of two-dimensional HMBC spectra of cholesteryl acetate recorded on a Bruker Avancell 400 MHz spectrometer (A) with the standard HMBC pulse sequence (Figure 1), and (B) with the IMPACT-HMBC experiment depicted in Figure 30. The same contour levels are used for all spectra. In (A), F, ridges are still visible (indicated by a vertical arrow), while they are very efficiently suppressed in (B). The proposed sequence results in signals with no coupling structure, as a result of the incorporation of a constant-time period. The improved peak dispersion is shown for the correlation between C-3 and H-2 (expanded in the small boxes). Asterix and the dashed box indicate residual Vch signals. The measurement duration was 22 min for both experiments.

Saaby S, Knudsen KR, Ladlow M, Ley SV (2005) The Use of a Continuous Flow-Reactor Employing a Mixed Flydrogen-Liquid Flow Stream for the Efficient Reduction of Imines to Amines. Chem Commun 23 2909-2911 Seebach D, Overhand M, Kilhnle FNM, Martinoni D, Oberer L, Hommel U, Widmer H (1996) Beta-Peptides Synthesis by Arndt-Eistert Homologation with Concomitant Peptide Coupling. Structure Determination by NMR and CD Spectroscopy and by X-ray Crystallography. Helical Secondary Structure of a Beta-Hexapeptide in Solution and its Stability Towards Pepsin. Helv Chim Acta 79 913-941... 

The possible mechanism for the formation of C—C coupled (1) and decoupled (2) bimetallic complexes from Cp2M has been investigated [1 lb,c]. We followed a stepwise procedure to arrive at a model that was practical and at the same time realistic. In the first stage, the substituted cyclopentadienyls were replaced by Cp and the substituents on acetylides and butadiynes were replaced by H. The relative energies showed that, the C—C coupled structure 1 for M = Ti when L = Cp and R = H is more stable than 2 by 3 kcal/mol, while 2 is calculated to be 14.8 kcal/mol... 

As written, this set of equations provide the dynamic model for the Petl3mk column. Since a design for the column must first be obtained, the same set of equations but written for steady state conditions provides the basis for such a design problem. In any case, the model shows a coupled structure because of the recycle streams between the two columns such that the full set of equations must be solved simultaneously. 

Eksterowicz, J. E., Evensen, E., Lemmen, C., et al. (2002) Coupling structure-based design with combinatorial chemistry application of active site derived pharmacophores with informative library design. J. Mol. Graph. Model. 20, 469-477. 

FeMoco, both as a constituent of the FeMo protein and an isolated entity, has been the subject of detailed spectroscopic examination. 57Fe Mossbauer and EPR studies of the cofactor have been interpreted in terms of an S = centre that contains one molybdenum and ca. six irons in a spin-coupled structure. The EPR signal serves as a valuable fingerprint of FeMoco furthermore, release of FeMoco from the FeMo protein produces an EPR spectrum with broader features, but the same profile, thereby indicating that the core of this cluster is little changed by the extraction procedure. Treatment of FeMoco with ca. one equivalent of... 

SjogrenT, Svensson-Ek M, Hajdu J, Brzezinski P. Proton-couple structural changes upon binding of carbon monoxide to cytochrome cdl A combined flash photolysis and X-ray crystallography study. Biochemistry 2000 39 10967-74. 

Sjoergen, T., Svenson-Ek, M., Hajdu, I., and Brzezinski, P. (2000) Proton-coupling structural change upon binding of carbon monoxide to cytochrome cdi a combine flash... 

J. H. Prestegard J. Glushka, Residual Dipolar Couplings Structure and Dynamics of Glycolipids. In NMR Spectroscopy of Glycoconjugates J. Jimenez Barbero, T. Peters, Eds. Wiley-VCH Weinheim, 2002 pp 231-245. 

This expansion of the total electronic wavefunction is very compact, and provides a great deal of physical and chemical visuality. The spin-coupled structure (18) by itself reproduces with very reasonable accuracy all the features of a ground-state molecular potential energy surface. For example the spin-coupled function typically yields 85% of the observed binding energy, and equilibrium internuclear separations are accurate to 0.01 A. This function consequently dominates expansion (17) for all nuclear geometries. The various excited structures provide angular and other types of correlation as an extra quantitative refinement but do not alter the qualitative picture. 

The spin-coupled VB calculations comprised one-, two- and three-fold excitations from the original spin-coupled structure, and give rise to 400 spatial configurations or 592 spin-coupled structures. In Fig. 6 are shown... 

It is worth noting that the bound BH(X S ) + H and repulsive BH (3 S ) + H states become degenerate at large values of Pbh- This is because both give B(2s 2p P) + H + H as dissociation products. Otherwise it is obvious that these two states differ widely from one another. The chosen set of spin-coupled structures provides a correct description of both. 

Now, because of their construction, the spin-coupled structures form bases for irreducible representations of the general linear group GL(n) . The particular irreducible representation is determined by N and S, i.e. the same two quantities which determine the irreducible representation of the symmetric group. In addition, if all the symmetry-allowed spin couplings k are included, the orbitals occurring in a particular structure may be ordered in... 

Figure 3.14. The influence of data acquisition times on the ability to resolve fine structure. Longer acquisition times correspond to higher digitisation levels (smaller Hz/pt) which here enable characterisation of the coupling structure within the double-doublet (J = 6 and 2 Hz).

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