Dipyridones

Dipyridone, see Diquat Disacryl, see Acrolein Disulfoton oxon sulfone, see Disulfoton Disulfoton oxon sulfoxide, see Disulfoton Disulfoton sulfone, see Disulfoton Disulfoton sulfoxide, see Disulfoton 2,2 -Dithiobis-ethanol, see Phorate Dithiophosphoric acid, see Phorate... 

Chemical/Physical. Decomposes at 320 °C (Windholz et al., 1983) emitting toxic fumes of bromides and nitrogen oxides (Lewis, 1990). Diquat absorbs water forming well-defined, pale yellow crystalline hydrate but in aqueous alkaline solutions, diquat decomposes forming complex colored products including small amounts of dipyridone (Calderbank and Slade, 1976). 

Scheme 3.3 Self-assembly behavior of self-complementary (8) and non-self-complementary (9) dipyridone modules.

Intramolecular photodimerization of 2-pyridones provides a series of primary photoproducts, the structures of which were a function of the chain length comecting the two reactive centers." The initially formed dimers were characterized as being derived from a photochemically allowed [2 + 2] cycloaddition process in each case examined. A particularly interesting example from this study in terms of [4 + 4] cycloaddition chemistry is the conversion of dipyridone (114) into Ae net [4 + 4] dimer (115) via a facile thermal rearrangement. " Further irradiation of the [4 + 4] species (115) produced a second [2 + 2] adduct that was isomeric with the initially formed metastable species. 

Structure 5 is one example of a number of dipyridones that incorporate different spacer groups.Since 5 was designed to be self-complementary, it was anticipated that it would self-associate to produce a dimer of type 6. Indeed, this was shown to be so in chloroform (> 90% dimer) by means of vapour pressure osmometry. X-Ray crystallography also confirmed that the dimer persists in the solid state. The behaviour of 5 contrasts markedly with that of 7 which was designed to be complementary only in an offset manner, such that linear polymerisation might be promoted. Under the dilute conditions of measurement, vapour pressure osmometry indicated that this species remains predominantly monomeric in chloroform however. X-ray diffraction confirmed that 7 adopts the linear polymeric structure illustrated by 8 in the solid state. As anticipated, since self-association involves hydrogen bonding, both 5 and 7 were shown to exist only as monomers in the pro-tic solvent methanol. 

In an extension of the above study, the solution behaviour of the dipyridone 9,... 

Symmetric dipyridones form 1-D arrays through pairs of N-H O interactions. Similarly, diacids, both aliphatic and aromatic, commonly produce infinite 1-D chains in the absence of strong competitive hydrogen-bond acceptors. 

Fig. 17. Dimers and ribbons formed by asymmetric 20 and symmetric dipyridones 21...

In aqueous alkahne solutions, diquat decomposes forming complex colored products including small amounts of dipyridone (Calderbank and Slade, 1976). 

Figure 13 Two classes of self-assembly (a) homomeric with identical dipyridones and (b) heteromeric with cytosine and guanine.

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