Chemical reactivity from an activation strain perspective

Abstract

Chemical reactions are ubiquitous in the universe, they are at the core of life, and they are essential for industrial processes. The drive for a deep understanding into how something...

Origin of asynchronicity in Diels–Alder reactions

“…Next, we examine the physical factors leading to the enhanced reactivity of the LA-catalyzed compared to the uncatalyzed Diels–Alder reactions, by applying the activation strain model (ASM) of reactivity. 12 Table 1 shows the results of the activation strain analyses at consistent, transition state-like geometries with a C B ⋯C β bond length between B and O–LA of 2.118 Å (see ESI, † Fig. S2 for complete activation strain and energy decomposition analysis diagrams).…”

“…Performing this analysis at a consistent point along the reaction coordinate (near all transition state structures), rather than on the individual transition state structures alone, ensures that the results are not skewed by the position, earlier or later, of the transition state. 12,20 Note that for O–H+ the barrierless formation of the first C–C bond is analyzed. 28 The trend in total energies at the consistent geometry, Δ E *, in Table 1 follows that of the actual reaction barriers Δ E ‡ , namely, the uncatalyzed reaction ( O ) goes with the highest, i.e.…”

“…The activation strain model of reactivity (ASM, 12 also known as the distortion/interaction model 25 ), is a fragment-based approach based on the idea that the energy of a reacting system, i.e. , the potential energy surface, can be described with respect to, and understood in terms of the characteristics of the original reactants.…”

“…The orbital interaction energy, Δ E oi (ζ), accounts for polarization and charge transfer between the fragments, such as HOMO–LUMO interactions. A detailed, step-by-step guide on how to perform and interpret the ASM and EDA can be found in ref. 12 a .…”

“…These Lewis acid catalysts were selected due to their ability to make the Diels–Alder reaction more asynchronous. The activation strain model (ASM) 12 of reactivity in combination with Kohn–Sham molecular orbital (KS-MO) 13 theory and the matching canonical energy decomposition analysis (EDA) 14 were employed to gain quantitative insights into the origin of asynchronicity in these Diels–Alder reactions. This computational approach has been proven to be reliable for the understanding of fundamental processes in organic chemistry.…”