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In order to attack the C atom, the nucleophile must approach in line with the C-LG (leaving group) bond from the back, where the benzene ring lies. It follows the general rule for which S N 2 reactions occur only at a tetrahedral carbon atom. The S N 1 mechanism is possible but very unfavourable unless the leaving group is an exceptionally good ...
Sodium methoxide is prepared by treating methanol with sodium: 2 Na + 2 CH 3 OH → 2 CH 3 ONa + H 2. The reaction is so exothermic that ignition is possible. The resulting solution, which is colorless, is often used as a source of sodium methoxide, but the pure material can be isolated by evaporation followed by heating to remove residual methanol.
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 − ).
In this type of substitution reaction, one group of the substrate participates initially in the reaction and thereby affects the reaction. A classic example of NGP is the reaction of a sulfur or nitrogen mustard with a nucleophile, the rate of reaction is much higher for the sulfur mustard and a nucleophile than it would be for a primary or secondary alkyl chloride without a heteroatom.
Grignard reagents are nucleophiles in nucleophilic aliphatic substitutions for instance with alkyl halides in a key step in industrial Naproxen production: Naproxen synthesis. In the Bruylants reaction, a nitrile can be replaced by the Grignard nucleophile, rather than the Grigard attacking the nitrile to form an imino structure. [17]
In many nucleophilic reactions, addition to the carbonyl group is very important. In some cases, the C=O double bond is reduced to a C-O single bond when the nucleophile bonds with carbon. For example, in the cyanohydrin reaction a cyanide ion forms a C-C bond by breaking the carbonyl's double bond to form a cyanohydrin.
An application of HSAB theory is the so-called Kornblum's rule (after Nathan Kornblum) which states that in reactions with ambident nucleophiles (nucleophiles that can attack from two or more places), the more electronegative atom reacts when the reaction mechanism is S N 1 and the less electronegative one in a S N 2 reaction.
The Williamson ether reaction follows an S N 2 (bimolecular nucleophilic substitution) mechanism. In an S N 2 reaction mechanism there is a backside attack of an electrophile by a nucleophile and it occurs in a concerted mechanism (happens all at once).