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Acyl compounds react with nucleophiles via an addition mechanism: the nucleophile attacks the carbonyl carbon, forming a tetrahedral intermediate. This reaction can be accelerated by acidic conditions, which make the carbonyl more electrophilic , or basic conditions, which provide a more anionic and therefore more reactive nucleophile.
This is called a nucleophilic addition reaction and it plays a central role in the biological chemistry taking place in many biosyntheses in nature, and is a central "tool" in the reaction toolkit of modern organic chemistry, e.g., to construct new molecules such as pharmaceuticals.
This type of reaction is also called a 1,2-nucleophilic addition. The stereochemistry of this type of nucleophilic attack is not an issue, when both alkyl substituents are dissimilar and there are not any other controlling issues such as chelation with a Lewis acid, the reaction product is a racemate. Addition reactions of this type are numerous.
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 ...
This free-energy relationship relates the pseudo first order reaction rate constant (in water at 25 °C), k, of a reaction, normalized to the reaction rate, k 0, of a standard reaction with water as the nucleophile, to a nucleophilic constant n for a given nucleophile and a substrate constant s that depends on the sensitivity of a substrate to ...
The 1,6-Michael reaction proceeds via nucleophilic attack on the 𝛿 carbon of an α,β-,𝛿-diunsaturated Michael acceptor. [34] [35] The 1,6-addition mechanism is similar to the 1,4-addition, with one exception being the nucleophilic attack occurring at the 𝛿 carbon of the Michael acceptor. [35]
These so-called activation parameters give insight into the nature of a transition state, including energy content and degree of order, compared to the starting materials and has become a standard tool for elucidation of reaction mechanisms in physical organic chemistry.
Burgi-Dunitz trajectory. The nucleophilic attack on the carbonyl group proceeds via the Bürgi-Dunitz trajectory.The angle between the line of nucleophilic attack and the C-O bond is greater than 90˚ due to a better orbital overlap between the HOMO of the nucleophile and the π* LUMO of the C-O double bond.