Theoretical methods solid-state structures

In concluding this review it must be noted that there are many other techniques that are being utilized to increase our understanding about the structure of synthetically important carbanions. A partial listing of these techniques would include the theoretical approaches taken by Schleyer, Streitweiser, Houk and others and classical spectroscopic techniques. There exist also a number of useful NMR techniques in addition to the 2D-HOESY method previously mentioned. These NMR techniques include analysis of chemical shifts, Li- N spin-spin splitting, Li quadrupolar coupling o and rapid injection which has proven useful as a technique for structural investigations of aliphatic carba-nions. Last, but certainly not least, the excellent thermochemical measurements recently reported by Arnett and coworkers serve to correlate the solid state structural studies with solution species. A... 

Further progress has been reported in the chemistry of CT X, -p -bonded systems. Full details of such systems stabilised by intramolecular coordination, as in, e.g., 334, have been described. The kinetically stable system 335 has been prepared and its solid state structure determined . The P-halobis(imino)-CT -phosphoranes 336 have also been prepared, and detailed NMR studies of bis(imino) phosphoranes reported . Quin s group has continued studies of the generation and characterisation of reactive a X -systems, e.g., 337 ". Methods for the generation of monomeric metaphosphate esters in solution have been investigated. A theoretical approach has been used to probe the mechanism of the reaction between phosphanylnitrenes 338 and boranes. The thiophosphonic anhydride 339 behaves as a source of the dithioxophosphorane... 

The first problem to address is that of the experimental and theoretical tools . Single-crystal X-ray crystallography has, of course, been the method of choice for the determination of the solid-state structures of transition metal clusters. Their structural variability, complexity, and even, at times, unpredictability preceded, in terms of experimental challenge, that of large biomolecules and proteins. New scientific challenges such as, on the one hand, the advent of area detector techniques and powerful X-ray radiation sources and, on the other hand, the use of variable temperature techniques, combined with spectroscopic solid-state methods enables in depth investigation of the temperature-dependence of solid-state molecular and crystal structures and the study of their phase transitional behavior. 

Complementarity of Theoretical and NMR Methods in Assignment of the Solid-State Structure of Peptides... 

COMPLEMENTARITY OF THEORETICAL AND NMR METHODS IN ASSIGNMENT OF THE SOLID-STATE STRUCTURE OF PEPTIDES... 

Trykowska el al. have reported solid-state structure of O-aminoalkyl derivatives of 7-hydroxy-4-methylcoumarin by experimental CPMAS NMR and X-ray diffraction methods and theoretical DPT calculations. ... 

The probe molecules of greatest historical interest in catalysis are the Hammett indicators [13]. The difficulty of making reliable visual or spectrophotometric observations of the state of protonation of these species on solids is well known. We have recently carried out the first NMR studies of Hanunett indicators on solid acids [ 14]. This was also the occasion of the first detailed collaboration between the authors of this article, and theoretical methods proved to strongly compliment the NMR experiments. The Hanunett story is told after first reviewing the application of theoretical chemistry to such problems. Central to the application of any physical method in chemistry is the process of modeling the relationship between the observables and molecular structure. However often one does this, it is rarely an exact process. One can rationalize almost any trend in isotropic chemical shift as a function of some variation in molecular structure - after the fact, but the quantitative prediction of such trends in advance defies intuition in most nontrivial cases. Even though the NMR spectrum is a function... 

To characterize the composition and structure of metal complexes formed in extraction processes (either in the aqueous phase or at the interface), various experimental methods are used. Theoretical methods become helpful in complementing the results if the spectroscopic data are not sufficient to fully describe the structure, if crystals suitable for diffraction studies are not available, etc. Moreover, the calculations can result in reliable structures of the complexes or ligands in solution, which are often different from those observed in the solid state. 

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