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The reaction potential energy surface (PES), and thus the mechanism of bimolecular nucleophilic substitution (SN2), depends profoundly on the nature of the nucleophile and leaving group, but also on the central, electrophilic atom, its substituents, as well as on the medium in which the reaction takes place. Here, we provide an overview of recent studies and demonstrate how changes in any one of the aforementioned factors affect the SN2 mechanism. One of the most striking effects is the transition from a double‐well to a single‐well PES when the central atom is changed from a second‐period (e. g. carbon) to a higher‐period element (e.g, silicon, germanium). Variations in nucleophilicity, leaving group ability, and bulky substituents around a second‐row element central atom can then be exploited to change the single‐well PES back into a double‐well. Reversely, these variations can also be used to produce a single‐well PES for second‐period elements, for example, a stable pentavalent carbon species.

This report describes a density functional theory investigation into the reactivities of a series of aza‐1,3‐dipoles with ethylene at the BP86/TZ2P level. A benchmark study was carried out using QMflows, a newly developed program for automated workflows of quantum chemical calculations. In total, 24 1,3‐dipolar cycloaddition (1,3‐DCA) reactions were benchmarked using the highly accurate G3B3 method as a reference. We screened a number of exchange and correlation functionals, including PBE, OLYP, BP86, BLYP, both with and without explicit dispersion corrections, to assess their accuracies and to determine which of these computationally efficient functionals performed the best for calculating the energetics for cycloaddition reactions. The BP86/TZ2P method produced the smallest errors for the activation and reaction enthalpies. Then, to understand the factors controlling the reactivity in these reactions, seven archetypal aza‐1,3‐dipolar cycloadditions were investigated using the activation strain model and energy decomposition analysis. Our investigations highlight the fact that differences in activation barrier for these 1,3‐DCA reactions do not arise from differences in strain energy of the dipole, as previously proposed. Instead, relative reactivities originate from differences in interaction energy. Analysis of the 1,3‐dipole–dipolarophile interactions reveals the reactivity trends primarily result from differences in the extent of the primary orbital interactions.

The Lewis acid(LA)‐catalyzed Diels–Alder reaction between isoprene and methyl acrylate was investigated quantum chemically using a combined density functional theory and coupled‐cluster theory approach. Computed activation energies systematically decrease as the strength of the LA increases along the series I2

General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.