Isomerism, dynamic

Lowry concluded with a discussion of "dynamic isomerism," which might be of three kinds transfer of (1) a radical (2) a hydrogen ion or proton or (3) an electron. The latter two categories he called "prototropy" and "electrotropy."64 Physical proofs for the ionic hypothesis were among Lowry s topics... 

In 1895, Armstrong published some twenty-five papers jointly with members of his chemical laboratory. A report to the alumni in 1903 mentions work in five subjects undertaken by Armstrong and some of his proteges radioactivity (H. Armstrong and Lowry), dynamic isomerism (Lowry), stereochemistry of noncarbon elements (Pope), the chemistry of camphor (M. O. Forster), and tautomerism (Lapworth).34... 

Thomas Lowry, "Dynamic Isomerism." Report of the Committee, consisting of Professor H. E. Armstrong (Chairman), Dr. T. M. Lowry (Secretary), Professor Sydney Young, Dr. C. H. Desch, Dr. J. J. Dobbie, Dr. M. 

Lowry, Thomas Martin. "Dynamic Isomerism." BAAS Rep. Winnipeg, 1909 (1910) 135143. 

In 2007, in a very exhaustive paper, Paradies and coworkers carried out a comprehensive structural characterization of the colorless and yellow forms of Af-hydroxyphthalimide (NHPI) by means of single-crystal X-ray diffraction, FTIR and Raman spectroscopies and scanning electron microscopy. In the yellow form, the Af-hydroxyl group is significantly out of the plane (1.19°), but the Af-hydroxyl group in the colorless form is only 0.06° out of the plane. The irreversible conversion of the colorless crystalhne form to the yellow crystalhne form is more like a dynamic isomerism than a polymorphic transformation. 

Aq. soln. of sodium chlorate are optically inactive no matter whether the soln. be made from the right- or left-handed crystals—presumably because for a state of stable equilibrium—dynamic isomerism—equal quantities of the two isomers are required, and when the aq. soln. of either form is allowed to recrystallize, H. Landolt7 found equal proportions of the two forms are obtained but D. Gernez showed that if a right- or left-handed crystal be added to the undercooled soln., only one... 

Femtosecond visible pump - midinfrared probe setup for the study of protein dynamics. Isomerization in Photoactive Yellow Protein... 

No final or absolute decision is therefore yet possible. By analogy with other cases of a similar type amongst organic compounds, the possibility of a dynamic isomerism must not be left out of consideration. It is quite possible that in sulphurous acid solution, molecules of the symmetrical and the unsymmetrical constitution may be present, side by side, in equilibrium with one another, and that even in solutions of the salts a similar condition of equilibrium may exist. Indeed, the distinctly contradictory nature of some of the chemical evidence favours this view. 

Valence tautomerism is responsible for the photochromic transformation exhibited by the xanthenone (143). This phenomenon is a type of dynamic isomerism in which the primary change is a shift in the position of the valence bonds as illustrated in Scheme 16 (68JOC3469). 

The behaviour of sodium ethyl aceto-acetate towards chloracetic ester and chloroformic ester respectively, indicates that the compound exhibits dynamic isomerism because in the first reaction it behaves as though sodium were directly united to carbon, and in the second reaction as though the sodium were united to oxygen ... 

Snccino-succinic ester, like phloroglucin, exhibits dynamic isomerism (tautomerism), behaving under some conditions as a lceto-body, and under other conditions as a hydroxylic, or phenolic body having this structure ... 

In the course of our earlier studies on terpenylboranes we developed a simple transformation of a- into 3-pinene," and a stereoselective synthesis of allylic alcohols by the reduction of vinylic epoxides.12 An extension of these studies to contrathermo-dynamic isomerization of a-thujene, 2- and 3-carene,13 and kinetic resolution of vinylic epoxides by the reduction with terpenylboranes,14 is described. 

At first glance this definition seems straightforward. What are some of the complications For flexible molecules McCrone would include conformational polymorphs, wherein the molecule can adopt different conformations in the different crystal structures (Corradini 1973 Panagiotopoulis et al. 1974 Bernstein and Hagler 1978 Bernstein 1987). But this is a matter of degree dynamic isomerism or tautomerism... 

McCrone (1965) and Haleblian and McCrone (1969) pointed out that pseudopolymorphism has been used to describe a number of phenomena that are related to polymorphism among them are desolvation, second-order transitions (some of which may be considered examples of polymorphism), dynamic isomerism, mesomorphism. 

While this system falls somewhere on the fuzzy line between polymorphism and dynamic isomerism we agree with McCrone (1965) and Threlfall (1995) that this phenomenon should not be described as pseudopolymorphism. 

The thermomicroscopic differentiation between two phases that are known to be related either by polymorphism or dynamic isomerism is elegantly straightforward. The two phases should be melted side by side between a microscope slide and a cover slip, and then allowed to crystallize. Two possibilities exist for the subsequent crystallization events. In the case of polymorphism, the crystal fronts from the two melts will grow at a constant velocity until they come into contact, at which point one phase will grow through the other, due to a solid-solid transformation to the stable phase at that temperature. In the case of dynamic isomerism, the two crystal fronts would slow down as they approach each other, and in the so-called zone of mixing (McCrone 1965) a eutectic could appear. 

First, it is necessary to eliminate tautomerism or dynamic isomerism by determining that the two materials give identical melts. X-ray diffraction can determine that crystal strain (which can be mistaken for polymorphism) is not a factor. Then, McCrone... 

Titanium complexes of oxacalix[3]arenes - synthesis and mechanistic studies of their dynamic isomerization, P. D. Hampton, C. E. Daitch, T. M. Alam, Z. Bencze and M. Rosay, Inorg. Chem., 1994, 33, 4750. 

In studying the fusion and solidification of those substances which exhibit the relationships of dynamic isomerism, it has to be borne in mind that the phenomena observed will vary somewhat according as the reversible transformation of the one form into the other takes place with measurable velocity at temperatures in the neighbourhood of the melting-points, or only at some higher temperature. If the transformation is relatively very rapid, the system will behave like a one-component system, but if the isomeric change is comparatively slow, the behaviour will be that of a two-component system. 

Naveau l , rejecting Schill s conclusions, presented data supporting the existence of a dynamic Isomerism between two stereo-isomers of unknown configuration. 

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