We show that, all other conditions being equal, bond cleavage in the middle of molecules is entropically much more favored than bond cleavage at the end. Multiple experimental and theoretical approaches have been used to study the selectivity for bond cleavage or dissociation in the middle versus the end of both covalent and supramolecular adducts and the extensive implications for other fields of chemistry including, e.g., chain transfer, polymer degradation, and control agent addition are discussed. The observed effects, which are a consequence of the underlying entropic factors, were predicted on the basis of simple theoretical models and demonstrated via high-temperature (HT) NMR spectroscopy of self-assembled supramolecular diblock systems as well as temperature-dependent size-exclusion chromatography (TD SEC) of covalently bonded Diels-Alder step-growth polymers.
Bibliographical noteFunding Information:
C.B.-K., M.L.C., and A.L. are grateful for continued support from and the excellent collaboration with Evonik Industries. C.B.-K. additionally acknowledges funding from the KIT via the Helmholtz association (BIFTM and STN programs) as well as the German Research Council (DFG). M.L.C. acknowledges generous allocations of supercomputing time on the National Facility of the National Computational Infrastructure and an Australian Research Council Future Fellowship.
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- entropic effects
- supramolecular chemistry