Deformation isomerism

Berson and Gajewski have given an explanation of their experimental results in which the products of the reaction are determined by the formation of the deformationally isomeric ions 66 and 67. As an alternative, they propose that the different results in the two systems may be attributed to transitory differences in the local environment of the cations rather than to two structurally different cations , an explanation that encompasses the coimter-ion mechanism given above. The reader is referred to the original work for details. 

Porphyrins that contain Ru-Mo and Os-Mo dinuclear complexes was reported by Collman et al One of the isolated complexes, [RuMo(OEP)(TPP)][PF6] 30 (OEP = octaethylporphyrin, TPP = tetraphenylporphyrin), possesses a unique deformational isomerism. The Ru-Mo metal-metal bonds of the two molecules in the asymmetric unit are of different lengths. 

A theoretical investigation of the use of NMR lineshape second moments in determining elastomer chain configurations has been undertaken. Monte Carlo chains have been generated by computer using a modified rotational isomeric state (RIS) theory in which parameters have been included which simulate bulk uniaxial deformation. The behavior of the model for a hypothetical poly(methylene) system and for a real poly(p-fluorostyrene) system has been examined. Excluded volume effects are described. Initial experimental approaches are discussed. 

Rotational Isomeric State Model with Deformation... 

An early application was to the pathway for conformational isomerization of molecules Ar3Z, with three aromatic rings on the same centre (Mislow, 1976). Typically the system is pyramidal (tetrahedral overall where there is a fourth substituent on Z), and the rings are close enough in space that they cannot rotate independently about the Z-Ar bond. Triphenylphosphine oxide, to take a specific example, crystallizes in a propeller conformation [4 Z = P=OJ which is chiral, with all three benzene rings rotated in the same sense from the relevant C-P-O plane. A study (Bye et al., 1982) of deformations from this geometry for more than 1000 related structures in various environments allowed a detailed description of the pathway for... 

In symmetric overcrowded or otherwise strained ethylenes, the strain may be partially released by rotation around the C=C bond or by other deformations, and the barrier to E-Z isomerization may be lowered compared to that of ethylene by ground state strain and by delocalization of the double-bond ir electrons into unsaturated substituents, forming a diradical transition state. The importance of the delocalization effect is illustrated by the low barrier (AC o = 23.2 kcal/ mol) in the diphenoquinone 125 (145), in which the ground state strain must be rather low. 

A transition complex which is consistent with the low energy of activation of the isomerization involves the simultaneous deformation (twisting) of the cyclobutene ring with the stretching of the carbon-carbon bond opposite the double bond ... 

This reinforces a view that the thermal isomerization, while perhaps assisted by deformations originating near the pyrrole nitrogens, does not require severe ruffling of the porphyrin macrocycle. 

The above mentioned deformation in the porphyrin diacid results in decreases in the free energy of activation for thermal atrop-isomerization, AG, of 2-3 kcal/mole compared to the corresponding free bases ( l) Even in the thermal isomerization the greater ground state stability of the trans-2,2 compared to the other isomers is apparent, although not nearly so much so as in the corresponding excited state. 

Boldyreva EV, Sidelnikov AA, Chupakhin AP, Lyakhov NZ, Boldyrev VV (1984) Deformation and fragmentation of crystals of [Co(NH3)5N02]X2 (X = Cl , Br , N03 ) during photochemical linkage isomerization. Proc Acad Sci USSR 277 893-896... 

The normal mode calculation was used to elucidate the rotational isomerization equilibrium of the [C4CiIm]X liquids. In the wave number region near 800-500 cm, where ring deformation bands are expected, two Raman bands appeared at —730 cm and —625 cm in the [C4C4lm]Cl Crystal (1). In the [C4CiIm]Br these bands were not found. Here instead, another couple of bands appeared at —701 and —603 cm T To assist the interpretation of the spectra, the normal modes of vibrations calculated by Hamaguchi et al. [50] are shown in Figure 12.8. 

The infrared (IR) spectra of 1,10-phenanthroline, its hydrate and perchlorate in the region 600-2000 cm-1 have been obtained, and the principal features of the spectra interpreted.66 Further studies on the IR spectra of 1,10-phenanthroline,67-69 substituted 1,10-phenanthrolines,70,71 and 1,7-phenanthroline67 have also been reported. The IR spectrum of 4,7-phenanthroline in the region 650-900 cm-1 has been analyzed, and the C—H out-of-plane deformation frequencies were compared with those of phenanthrene and benzo[/]quinoline.72 The IR spectra of salts of 1,10-phenanthroline have been taken, and the NH vibrations determined.28,73 Infrared spectroscopy has been used to detect water associated with 1,10-phenanthroline and some of its derivatives on extraction into nitromethane from aqueous solution.74 The Raman spectrum of 1,10-phenanthroline has been compared with its IR spectrum.75 Recently, the Raman and IR spectra of all ten isomeric phenanthrolines were measured in solution and solid states, and the spectra were fully discussed.76... 

According to the current state of the theory, the deformation of polymeric networks must be accompanied not only by the intrachain conformational entropy changes but intrachain energy changes which depend on the conformational energies of macromolecules. Therefore, reliable experimental determination of these intrachain energy changes and their interpretation by means of isomeric state theory is of fundamental importance for polymer physics. 

The flexibility and extensibility of a crosslinked epoxy network are determined by the available glassy-state free volume. If the free volume is insufficient to allow network segmental extensibility via rotational isomeric changes then the brittle mechanical response of the epoxy glass is not controlled by the network structure but rather by macroscopic defects such as microvoids. For epoxies with sufficient free volume that allows plastic network deformation the mechanical response is controlled by the network structure. 

This chapter is concerned with the influence of mechanical stress upon the chemical processes in solids. The most important properties to consider are elasticity and plasticity. We wish, for example, to understand how reaction kinetics and transport in crystalline systems respond to homogeneous or inhomogeneous elastic and plastic deformations [A.P. Chupakhin, et al. (1987)]. An example of such a process influenced by stress is the photoisomerization of a [Co(NH3)5N02]C12 crystal set under a (uniaxial) chemical load [E.V. Boldyreva, A. A. Sidelnikov (1987)]. The kinetics of the isomerization of the N02 group is noticeably different when the crystal is not stressed. An example of the influence of an inhomogeneous stress field on transport is the redistribution of solute atoms or point defects around dislocations created by plastic deformation. 

Interest in thermotropic liquid crystals has focussed mainly on macroscopic properties studies relating these properties to the microscopic molecular order are new. Lyotropic liquid crystals, e.g. lipid-water systems, however, are better known from a microscopic point of view. We detail the descriptions of chain flexibility that were obtained from recent DMR experiments on deuterated soap molecules. Models were developed, and most chain deformations appear to result from intramolecular isomeric rotations that are compatible with intermodular steric hindrance. The characteristic times of chain motions can be estimated from earlier proton resonance experiments. There is a possibility of collective motions in the bilayer. The biological relevance of these findings is considered briefly. Recent similar DMR studies of thermotropic liquid crystals also suggest some molecular flexibility. 

Ferreti and coworkers110 have carried out an analysis of over 300 crystal structures of species which contain the R(X=)C—NR1R2 molecular fragment. In this survey it was found that, in the crystal, inter- or intramolecular forces can induce out-of-plane deformations of the fragment, so that the cis-trans isomerization pathway involves a transition state 21b. 

The experimental work here has shown that the deformation of the isomeric 9/2 states in the light thallium isotopes is increasing with decreasing neutron number while the 1/2 state remains relatively constant. This work shows the fallacy of assuming that a constant moment of inertia infers a constant deformation. Theoretically, this work has demonstrated an interesting aspect of the competition between quadrupole and pairing correlations in near-singly-closed-shell nuclei. 

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