Rate Acceleration through Dispersion Interactions: Effect of a Hemicarcerand on the Transition State of Inner Phase Decompositions of Diazirines

Abstract

Incarceration strongly increases the rate of the thermal decomposition of diazirine 1 to yield carbene 2. The increase of the inner phase rate is rationalized by a stabilization of the transition state through dispersion interactions between the breaking C−N bonds and one of the highly polarizable arene rings of the surrounding host 3.

Computational NMR Spectra of o‐Benzyne and Stable Guests and Their Hemicarceplexes

“…So far, the theoretical investigations of structures and dynamics of hemicarcerands have mainly involved force field (MM2, MM3, AMBER) and semiempirical calculations . Although these methods calculate geometries and energies with sufficient accuracy to predict complexation behavior, it has been shown to have problems describing the unusual environment inside a hemicarcerand or hemicarceplex cavity accurately.…”

Reactions Inside Carcerands

“…30,31 The thermolysis of diazirines is a common method to produce carbenes and its mechanism has been studied in detail (Figure 9.14 A). 32 Compared to the bulk phase, inner phase fragmentation of 48 is 15 -fold accelerated, that of 49 slightly faster (1.2 fold) and that of 50 2.4 -fold slower.…”

“…32 Compared to the bulk phase, inner phase fragmentation of 48 is 15 -fold accelerated, that of 49 slightly faster (1.2 fold) and that of 50 2.4 -fold slower. 30 Furthermore, all inner phase transition states are stabilized enthalpically by 2 -3 kcal mol − 1 , which, in the case of 49 and 50 , is partially or fully compensated by unfavorable entropic contributions to ∆ G ‡ . The unfavorable ∆ T ∆ S ‡ term likely results from loss of vibrational degrees of freedom as the guest expands upon reaching the transition state leading to a tighter hemicarceplex.…”

“…30 The mechanism of the phenylnitrene rearrangement 31 Inner phase photochemistry of phenylazide 94 inside hemicarcerand 4…”

Spontaneous Mechanical‐Like Motions

“…Rotation movements of molecules hosted in hemicarcerands have been extensively investigated [7,37] also because of their relevance to catalytic processes [38]. Rotation movements of molecules hosted in hemicarcerands have been extensively investigated [7,37] also because of their relevance to catalytic processes [38].…”