Why Study Materials in the Solid State

How NMR spectroscopy can work on solid samples without dissolution (sometimes even without grinding to a powder)—and how it differs from the fluid phase NMR with which most chemists are familiar—is the subject of the next 

Solid-state NMR is used in the analysis of ceramics (they are neither soluble nor meltable), biological cell membranes, wood, cellulose and other plant materials, bone, and even gemstones (any volunteers for solution NMR spectroscopy of 

Another application of solid-state NMR is in the study of solid-state conformation. In solution molecules tumble rapidly, and rotations about single bonds are fast recall that in solution spectra the three methyl protons are normally equivalent (Section 4.2). In the solid state many of these motions are restricted or suppressed entirely, and many of the chemical shift degeneracies to which we have become accustomed are now split. For example, pnra-dimethoxybenzene, structure 15-1, exhibits a solution l3C spectrum in which the two methoxy carbons are equivalent to each other, as are the two substituted aromatic carbons, and each set gives rise to a single resonance  

Lastly, molecular motion affects solid-state spectra just as chemical exchange does in solution (Chapter 10 and Section 14.2). Nuclear magnetic resonance provided the proof that benzene molecules, structure 15-2, rotate in place about their sixfold axes (Example 4.3) in the crystal above 90 K (Kelvins absolute temperature 0°C = 273 K)  

Below that temperature this thermally activated motion is frozen out. There is a characteristic change in the solid-state lineshape that clearly demonstrates the effect. Nuclear magnetic resonance can in such cases provide important information about molecular structure and dynamics in solids. 

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However, while the crystal structure of [Cl3ln P(m-anis)3 2] determined by X-ray crystallography is in line with the solid-state NMR data, this is not the case for [Cl3ln P(p-anis)3 2]. Both compoimds have been found to have only one independent position for the phosphorus atoms, i.e. all P positions are related by symmetry. We should therefore expect one resonance as is seen for [Cl3ln P(m-anis)3 2]. So why are there two resonances for [Cl3ln P(p-anis)3 2] The single crystalline material contains solvent dichloromethane molecules, while the powdered samples do not (as was proven by elemental analysis). Despite the fact that both NMR and X-ray diffraction studies were of the solid state, they have actually been carried out with two chemically different materials with different structures. 

Simultaneously, processes of plastic deformation, fracture and interactions with the environment, and counterbody can occur. The latter ones have been studied by mechanical engineers and tribologists, but the processes of phase transformations at the sharp contact have been investigated for only a few materials (primarily, semiconductors) and the data obtained so far can only be considered preliminary. One of the reasons for the lack of information may be the fact that the problem is at the interface between at least three scientific fields, that is, materials science, mechanics, and solid state physics. Thus, an interdisciplinary approach is required to solve this problem and understand how and why a nonhydrostatic (shear) stress in the two-body contact can drive phase transformations in materials. 

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