A new method implemented into a computer program (ConArch ) has been developed and applied to demonstrate the successful implementation of residual dipolar couplings (RDCs) in distance geometry (DG) calculations for the configurational assignment of chiral compounds. Unlike established protocols, the new approach combines floating chirality (fc) in 4D- and 3D-distance bounds driven dynamics (DDD) calculations with structural information from RDCs. Thus, relative configurations of chiral compounds were generated only by observables (e.g., NOEs, RDCs) rendering tedious evaluations of calculated structures against RDCs obsolete. We demonstrate the potential of this novel procedure by the simultaneous determination of the configuration and the conformation of three natural products, (-)-isopinocampheol (1), tubocurarine (2), and vincristine (3), as well as for diisopropylidene-β-d-fructopyranose (4).

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It is a broad consensus that the first step in the Gilch synthesis of poly(p-phenylene vinylenes) (PPVs) is 1,6-dehydrohalogenation of the 1,4-bis(halomethylene)benzene starting materials. The mechanism of the subsequent chain growth of the resulting R-halo-p-quinodimethane monomers, however, is still a matter of discussion. We re-evaluated the arguments presented for anionic chain propagation and set them against the evidence obtained for a radical mechanism. We conclude that (i) the initial dehydrohalogenation of the starting material represents an E 2 type 1,6-elimination without anionic intermediates, (ii) anionic chain propagation does not play a role in standard Gilch syntheses, but instead, (iii) the PPVs grow predominantly via radical chain polymerization. However, since the growing species are R,ω-macro-diradicals, recombination does not cause chain termination as in conventional radical polymerizations. This is one reason for the formation of very highmolecular weight PPVs. The monofunctional benzylhalogenides, sometimes assumed to act as initiators of anionic chain growth and to suppress gelation of the reaction mixtures by lowering the PPVs' molar masses, clearly do not play this role: while we could verify that these additives lower the risk of gelation, they are neither incorporated as end groups into the PPVs nor do they lower the molar masses. Instead, gelation is most probably due to physical crosslinking, induced by the very high entanglement density of the PPV chains immediately after their formation. Additives such as monofunctional benzylhalogenides seem to accelerate de-entanglement, possibly either by retarding the conversion of the still quite flexible poly(p-xylylene) (PPX) precursors into the semirigid PPVs, thereby giving the chains a better chance to de-entangle, or by preferential solvation and successful competition with segment-segment interactions. In agreement with the proposed mechanism is the reproducible observation that additives which antagonize gelation efficiently, simultaneously increase the magnitude of the only relevant side reaction of Gilch reactions, i.e., formation of [2.2]paracyclophanes.

A consistent picture is presented of the mechanistic details and intermediates of the Gilch polymerization leading to poly(p-phenylene vinylenes) (PPVs). In-situ generated p-quinodimethanes are shown to be the real monomers, and spontaneous formation of the initiating radicals is effected by dimerization of some of these monomers to dimer diradicals, the latter also being the reason why significant amounts of [2.2]paracyclophanes are formed as side-products. Chain propagation predominantly proceeds by radical chain growth, occasionally interrupted by polyrecombination events between the growing α,ω-macro-diradicals. Based on this knowledge, oxygen is identified as a very efficient molar-mass regulating agent, and the temporary gelation of the reaction mixtures is interpreted to be the consequence of a very high entanglement of the polymers immediately after their formation. Last but not least, it is rationalized why the usually considered constitutional defects in Gilch PPVs might not be the only and most relevant ones with respect to the efficiency and durability of the organic light emitting devices produced thereof, and why cis-configurated halide-bearing vinylene moieties should be perceived as being among the most critical candidates. These considerations result in the recommendation of straightforward measures that should lead to clearly improved PPVs.

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