Topochemical

If the flow is accompanied with CBA decomposition, the G value in Eq. (5) should be substituted with its time function, G(t). In the general case, thermal decomposition of a solid substance with gas emission is a heterogeneous topochemical reaction [22]. Kinetic curves of such reactions are S -shaped the curves representing reaction rate changes in time pass a maximum. At unchanging temperature, the G(t) function for any CBA is easily described with the Kolrauch exponential function [20, 23, 24] ... 

Enkelmann, V. Structural Aspects of the Topochemical Polymerization of Diacetylenes. Vol. 63, pp. 91-136. 

The intermediate formed in the two-stage decomposition of ZnS04 to ZnO has been variously reported as Zn502(S04)3 [781,798] and Zn30(S04)2 [784,799] reported values of E (Table 15) show little consistency. Decomposition has been described [799] as a topochemical reaction and the reverse process is slow if the ZnO (product) is not finely divided. 

Numerous intercalation reactions are known in which one reactant enters the lattice of the other. Such behaviour is conveniently illustrated by reference to two recent studies. Lithium undergoes a low temperature (298 K) topochemical reversible reaction with transition metal compounds (e.g. TiS2, NbSe3) [1211] in which the host lattice structure may be partially retained (e.g. in Li TiS2, LijNbSe3). The reaction [1212]... 

Consequently, 71300582 is a topochemical combination of CeCo3B2-type units with intermetallic clusters ... 

Trigonal-prismatic boron coordination predominates in borides, (Mj, Mj)2B with such structures as FcjP, anti-PbCl2 and NbCoB, which all are closely related NbCoB can be derived as the topochemical sum of the former two, and at higher T Nb(Ta)CoB transforms into the FcjP type. ... 

A mixed type CrB -t- FeB with an alternating sequence of slabs of FeB and CrB units is also known from the NbCoBj structure, which can be written as the topochemical sum ... 

Based on the topochemical description of the structure of M02BC = MoB MoC, the typieal B-chain element within the MoB unit becomes eonceivable. 

In late 1995, a team led by Vollhardt and Youngs reported their work on the strained PAM/PDM hybrid 80 [55]. Whereas the synthesis of 80 was not remarkable [Eq. (2)1, the solid-state behavior of the molecule was. X-ray crystallography revealed that the macrocycle was moderately strained, with the monoynes bent inward toward the center of the macrocycle by 3.9 -11.5° and the diyne unit bent outward by 8.6-11.2°. More importantly, crystal packing revealed that the diyne moieties were aligned in the prerequisite fashion for topochemical diacetylene polymerization to occur. Indeed, irradiation of crystals of 80 produced a violet... 

Just prior to Rubin s publication, another article appeared focusing on substructures of graphdiyne [63]. Like the other researchers in the PDM area, the Haley team was intrigued by the predictions of useful materials properties and technological applications for this and similar carbon-rich systems [5c, 50,52]. In particular, topochemical polymerization of a crystalline substructure of this network could produce an environmentally robust material with a large third-... 

Topochemical reactions of mixed crystals, inclusion complexes and... 

Direct transformation from 2,5-DSP to poly-2,5-DSP through 2,5-DSP oligomer in the crystal is shown in Scheme 1. This new reaction was named a four-centre-type photopolymerization. As well as being the first example of a topochemical reaction in a pure sense, the four-centre-type photopolymerization of 2,5-DSP crystals was the first example of photopolymerization via a step-growth mechanism. 

Since then, several review articles on topochemical phenomena in the... 

Of further particular interest was that the crystallographic results on 2,5-DSP and poly-2,5-DSP had pointed out a very important future possibility that an absolute asymmetric synthesis could be achieved if any prochiral molecule, e.g. an unsymmetrical diolefin derivative, could be crystallized into a chiral crystal and if the reaction of the chiral crystal proceeded in the same manner as the 2,5-DSP crystal with retention of the crystal lattice (Wegner, 1972, 1973). Such types of absolute asymmetric synthesis with a high enantiomeric yield have now been performed by topochemical [2+2] photoreaction of unsymmetric diolefin crystals (Addadi etal., 1982 Hasegawa et al., 1990 Chung et al., 1991a,b). 

In this chapter the topochemical [2+2] photoreactions of diolefin crystals are reviewed from the viewpoints of organic photochemistry, analysis of reaction mechanism, and crystallography as well as in terms of synthetic polymer chemistry and polymer physics. 

Characteristic features of topochemical [2+2] photoreactions of diolefin crystals... 

For the diolefin crystals, including unsymmetrical diolefin crystals, each packing of the a- and j8-types is further classified into translation- and centrosymmetry-type packings. Of the photoproducts derived from unsymmetrical diolefins, the cyclobutane ring which has the same substituent on a ring is called a homo-adduct, and that which has different substituents is called a hetero-adduct. Corresponding to the molecular arrangements of these diolefin crystals, four types of photoproducts (a- and jS-types, and homo- and hetero-adducts) are expected to be formed based on the topochemical principle, as shown in Scheme 2. 

The behaviour, which is not controlled by the topochemical rule but is greatly influenced by non-topochemical factors, is discussed in Section 2 in terms of molecular mobility, stabilization energy by orbital interaction and energy transfer in the crystals. 

As a typical example of topochemically prepared polymers, the nmr speetrum of the polymer derived from ethyl 4-[2-(2-pyrazyl)ethenyl]-cinnamate [l OEt] crystals by reaction (2), and the X-ray diffraction patterns of the same monomer and polymer are illustrated in Figs 1 and 2 (Hasegawa et al., 1989a). 

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