Regiochemical Effects on Molecular Stability: A Mechanochemical Evaluation of 1,4- and 1,5-Disubstituted Triazoles

Abstract

Poly(methyl acrylate) chains of varying molecular weight were grown from 1,4- as well as 1,5-disubstituted 1,2,3-triazoles. Irradiating acetonitrile solutions of these polymers with ultrasound resulted in the formal cycloreversion of the triazole units, as determined by a variety of spectroscopic and chemical labeling techniques. The aforementioned reactions were monitored over time, and the rate constant for the cycloreversion of the 1,5-disubstituted triazole was measured to be 1.2 times larger than that of the 1,4-disubstituted congener. The difference was attributed to the increased mechanical deformability of the 1,5-regioisomer as compared to the 1,4-isomer. This interpretation was further supported by computational studies, which employed extended Bell theory to predict the force dependence of the activation barriers for the cycloreversions of both isomers.

Mechanische Reversibilität der spannungskatalysierten Azid‐Alkin‐Cycloaddition

“…Dabei wurde eine geringfügig hçhere Wahrscheinlichkeit für das 1,5-Regioisomer vorgeschlagen. [2] Eine effiziente mechanisch induzierte Cycloreversion des 1,4-Regioisomers wurde jedoch später in einer weiteren und genaueren numerischen Simulation in Frage gestellt, [5] und die experimentelle Machbarkeit einer mechanisch induzierten Cycloreversion bleibt für beide Regioisomere spekulativ.…”

“…Scherkräfte,d ie durch implodierende Kaviationsblasen erzeugt werden, strecken diese Polymere und üben somit eine Zugkraft auf das gesamte Molekül aus.C ycloreversion konkurriert daher mit Abrissen in den gekoppelten Polymerketten. Es wurden daher auch unabhängige Simulation mit den am häufigsten benutzen Polymeren Polytetrahydrofuran (pTHF) [19] und Polymethacrylat (PMA) [2,20] durchgeführt, um die mechanische Stabilität der Polymere mit der Stabilität der Tr iazol-Moleküle zu vergleichen (siehe SI).…”

“…[2,5] Das Produkt der Kupfer-katalysierten Azid-Alkin-Cycloaddition (CuAAC; 1,4-substituiertes Regioisomer,A bbildung 1a) [6] wurde mit dem 1,5-Regioisomer aus der Ruthenium-katalysierten Reaktion (RuAAC; Abbildung 1a)v erglichen.[7] Für beide Regioisomere wurde Cycloreversion vorhergesagt. Dabei wurde eine geringfügig hçhere Wahrscheinlichkeit für das 1,5-Regioisomer vorgeschlagen.…”

Theoretical Approaches for Understanding the Interplay Between Stress and Chemical Reactivity

“…This model has been used to describe the effect of applied force on the rupture of bonds in pericyclic reactions [37] and the influence of anti-Hammond effects on barriers [116], and to explore how the regiochemistry of polymers attached to mechanophores can affect F-dependent changes in reaction rates. [117].…”

Mechanochemistry in Polymers with Supramolecular Mechanophores

“…The development of such materials systems roots in the realization that a myriad of natural processes happen through weak interactions, [5,6] such as the opening of transmembrane proteins, pre-catalytic enzyme-substrate complexes, or actin polymerization. While some of the early work in the area of polymer mechanochemistry had largely focused fundamental experiments that often involved sonochemical processes in dilute solution, [7][8][9][10][11] there has been a growing interest in solid materials that are capable of selectively transducing macroscopic mechanical forces into molecular events that trigger desirable macroscopic materials responses. [3,9,12,13] Indeed, this emerging design approach has recently permitted the development a range of adaptive solid-state polymers in which pre-programmed functions can be triggered by external stimuli, including mechanical triggers.…”