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A hydroxide ion acting as a nucleophile in an S N 2 reaction, converting a haloalkane into an alcohol. 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 ...
The nucleophile may be electrically neutral or negatively charged, whereas the substrate is typically neutral or positively charged. An example of nucleophilic substitution is the hydrolysis of an alkyl bromide , R-Br under basic conditions, where the attacking nucleophile is hydroxyl ( OH − ) and the leaving group is bromide ( Br − ).
For S N 2 reaction to occur more quickly, the nucleophile must easily access the sigma antibonding orbital between the central carbon and leaving group. S N 2 occurs more quickly with substrates that are more sterically accessible at the central carbon, i.e. those that do not have as much sterically hindering substituents nearby. Methyl and ...
This reaction does not depend much on the strength of the nucleophile, unlike the S N 2 mechanism. This type of mechanism involves two steps. The first step is the ionization of alkyl halide in the presence of aqueous acetone or ethyl alcohol. This step provides a carbocation as an intermediate.
Chemists have developed a geometric system to describe the approach of the nucleophile to the electrophilic center, using two angles, the Bürgi–Dunitz and the Flippin–Lodge angles after scientists that first studied and described them. [2] [3] [4] This type of reaction is also called a 1,2-nucleophilic addition.
Such nucleophile switches have occurred several times during evolutionary history, however the mechanisms by which this happen are still unclear. [ 17 ] [ 55 ] Within protease superfamilies that contain a mixture of nucleophiles (e.g. the PA clan ), families are designated by their catalytic nucleophile (C=cysteine proteases, S=serine proteases).
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As it does so, it replaces a weaker nucleophile, which then becomes a leaving group; the remaining positive or partially positive atom becomes an electrophile. The whole molecular entity of which the electrophile and the leaving group are part is usually called the substrate. [1] The most general form for the reaction may be given as