The canonical behavior of the entropic component of thermodynamic effective molarity. An attempt at unifying covalent and noncovalent cyclizations

01 Pubblicazione su rivista
DI STEFANO Stefano, Mandolini Luigi
ISSN: 1463-9076

This review article is concerned with the measurement, significance and applications of the concept of effective molarity (EM) in a large variety of cyclization reactions ranging from the formation of giant macromolecules in polymeric equilibrates to the self-assembly of cyclic supermolecules and supramolecular aggregates. Based on a dissection of EM into enthalpic and entropic components (EM = EMH × EMS), a careful examination of a large number of often overlooked quantitative studies of reversible cyclizations led to the definition of a set of "canonical" values of the entropic component EMS, expressed in graphical form by the plot of EMS∗ vs. n, where the asterisk denotes statistically corrected quantities, and n is the number of single bonds in the ring product. It is proposed that, to a useful approximation, all cyclization reactions comply with the "canonical" EMS∗ values, independent of the chemical nature of end groups and of the intervening chain, but solely dependent on the number n of rotatable bonds. The entropic component EMS∗ is approximately the same for cyclizations carried out under kinetic or thermodynamic control, and does not appear to be altered to a very significant extent by replacement of covalent with noncovalent bonds. © 2018 the Owner Societies.

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