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In 1962, Edwards and Pearson (the latter of HSAB theory) introduced the phrase alpha effect for this anomaly. He offered the suggestion that the effect was caused by a transition state (TS) stabilization effect: on entering the TS the free electron pair on the nucleophile moves away from the nucleus, causing a partial positive charge which can be stabilized by an adjacent lone pair as for ...
A later paper by Edwards and Pearson, following research done by Jencks and Carriuolo in 1960 [8] [9] led to the discovery of an additional factor in nucleophilic reactivity, which Edwards and Pearson called the alpha effect, [7] where nucleophiles with a lone pair of electrons on an atom adjacent to the nucleophilic center have enhanced ...
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases. Nucleophilic describes the affinity of a nucleophile to bond with positively charged ...
[1] [2] It is also known as the Pimentel–Rundle three-center model after the work published by George C. Pimentel in 1951, [3] which built on concepts developed earlier by Robert E. Rundle for electron-deficient bonding. [4] [5] An extended version of this model is used to describe the whole class of hypervalent molecules such as phosphorus ...
The electron pair (:) from the nucleophile (Nuc) attacks the substrate (R−LG) and bonds with it. Simultaneously, the leaving group (LG) departs with an electron pair. The principal product in this case is R−Nuc. The nucleophile may be electrically neutral or negatively charged, whereas the substrate is typically neutral or positively charged.
For mono- or diamido aluminyls, the aluminium empty p orbital is higher in energy than the ligand-based LUMO. Nevertheless, all analyzed aluminyl systems have a pretty similar aluminium lone pair - aluminium empty p orbital energetic gap of 3.42 to 4.06 eV, while the dialkyl aluminyl systems were, as expected, found to have the lowest HOMO-LUMO ...
Arrow pushing or electron pushing is a technique used to describe the progression of organic chemistry reaction mechanisms. [1] It was first developed by Sir Robert Robinson.In using arrow pushing, "curved arrows" or "curly arrows" are drawn on the structural formulae of reactants in a chemical equation to show the reaction mechanism.
As a result, the lone pair does not contribute to the aromatic system but importantly influences the chemical properties of pyridine, as it easily supports bond formation via an electrophilic attack. [26] However, because of the separation of the lone pair from the aromatic ring system, the nitrogen atom cannot exhibit a positive mesomeric effect.