Nucleophiles in the Sn2 reaction

The resulting cation is captured by the water molecule released in the first step and an exchange of protons leads to an amide. 

The overall process is called the Ritter reaction and is one of the few reliable ways to make a C-N bond to a tertiary centre. 

Reactions between ammonia and alkyl halides rarely lead to single products. The problem is that the primary amine product is at least as nucleophilic as the starting material and is formed in the reaction mixture so that it in turn reacts with the alkyl halide. 

Even this is not all If the alkylation were to continue, the secondary and the tertiary amines would be produced all together in the reaction mixture. The reaction comes to an end only when the tetra-alkylammonium salt R4N is formed. This salt could be the product if a large excess of alkyl halide R1 is used, but other more controlled methods are needed for the synthesis of primary, secondary, and tertiary amines. 

One solution for primary amines is to replace ammonia with azide ion N3, This is a linear tri-atomic species, nucleophilic at both ends—a little rod of electrons able to insert itself into almost any electrophilic site. It is available as the water-soluble sodium salt NaN3. 

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If the reaction is quenched with an alcohol, only the acyl halide reacts and this is a simple way to make a-bromoesters 38. The alternative product 39 is not formed. Water and alcohols are poor nucleophiles in the Sn2 reaction but better with carbonyl groups. 

Comparison of fluoride ion and iodide ion as nucleophiles in the SN2 reaction. Fluoride has tightly bound electrons that cannot begin to form a C—F bond until the atoms are close together. Iodide has more loosely bound outer electrons that begin bonding earlier in the reaction. 

The thiolate anion produced then acts as a nucleophile in the Sn2 reaction, the S m2 reaction with a thiolate anion as nucleophile... 

Now that we know how to make allylic chlorides of known structure—whether primary or secondary—we need to discover how to replace the chlorine with a nucleophile with predictable regios-electivity. We have said little so far about carbon nucleophiles (except cyanide ion) so we shall concentrate on simple carbon nucleophiles in the Sn2 reaction of allylic chlorides. 

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