Polymethylene-linked compound

In 1984, Weller s group reported MFEs on the primary photochemical processes of polymethylene-linked compounds containing electron acceptor and donor groups (A and D) with a nanosecond-laser photolysis technique in the presence of magnetic fields below 0.3 T [3a], Their reaction scheme is represented as follows ... 

This scheme is quite similar to that given for radical pairs by reactions (6-21a)-(6-21f), but there is no escape of component radicals in the case of biradicals. For each polymethylene-linked compound with A=pyrene and D=dimethylaniline in acetonitrile at room temperature, the group measured the intensity (Et(B)) of the transition absorption due to A. Their typical results are shown in Fig. 8-4. 

Weller s group also measured the MFEs on the exciplex fluoreseence intensity (1(B)) observed in acetonitril at room temperature for the same polymethylene-linked compounds with A=pyrene and D=dimethylaniline [3b]. The exciplex fluorescence (ho ex) is emitted from the following processes ... 

S)//(0T)) was found to only increase with increasing B from 0 mT. This MFE was similar to that observed for the intensity (Ej(By) of the transition absorption due to A and could be explained by the HFCM. Tanimoto et al. also observed similar MFEs on the exciplex fluorescence intensity for the polymethylene-linked compounds with A=phenanthrene and D=dimethylaniline [4]. Their Blc values are also listed in Table 8-1. 

Previously, the molecular structures of many thiuram di- [20-31] (see Fig. 1), mono- [32], trisulfides [33] and thiuram disulfide derivatives, in which R2NC(S)S- groups are linked by polymethylene chains [34], have been determined by single-crystal X-ray diffraction studies. A number of polycrystalline tetralkylthiuram disulfides and their cyclic analogs have also been recently studied by means of solid-state and CP/MAS NMR [31]. Assignments and and chemical shift data for eight (1-8) selected thiuram disulfide compounds and initial dithiocarbamate salts are shown in Table 1. The observed differences in and isotropic chemical shifts for these molecular systems can be attributed to simultaneous manifestation of the inductive effect of alkyl substituents and to the mesomeric effect of the dithiocarbamate groups discussed below. 

For some time, we have been interested in designing selective chemical modification reactions for coal with a particular emphasis upon characterizing the carbon skeleton of coal (2). The strategy for the approach starts with the working hypothesis that coal can be viewed as a three-dimensional macromolecule in which aromatic and hydroaromatic clusters are cross-linked to one another by various functional groups such as methylene units and polymethylene chains. In addition, the aromatic and hydroaromatic clusters, at least in bituminous coals, are assumed to be derived from polynuclear aromatic compounds (3, 4). 

Metal bipyridine complexes are classical mononuclear coordination compounds of photophysical interest [13]. Related binuclear (Fig. 11) and polynuclear species can be designed using a "double-bipyridine" ligand, obtained by linking together two bipyridine-type ligands via a short polymethylene chain [78-81]. 

Encapsulation of the flexible linkage connecting D and A into CD cavity would stretch the molecule changing its conformation similar to D-A system with rigid linkage. This may allow one to determine the fi value for the flexible linkage. This was demonstrated with polymethylene chain-linked aromatic-vi-ologen compounds 8 [20]. 

The properly of forming resinous products on reaction with other chemicals is one oi the most useful characteristics of formaldehyde and is the basis of its immense industrial importance in the si nthetio-resin industn. Under suitable conditions the molecules 01 many compounds are linked together by methylene groups when subjected to the action of formaldehyde. Phenol- and urea-formaldeliyde resins are polymethylene compounds 01 this type. 

In general, these nesins may be defined as mixtures of polymethylene compounds in which phenolic radicals are linked by methylene grouirs. They are broadly classified as belonging to two distinct types ... 

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