Nucleophilic attack halogen molecules

In intramolecular arylations, a new bond is created between two aromatic moieties of the same molecule or between an aromatic nucleus and an atom of a side-chain. Many intramolecular arylation reactions of homocyclic and heterocyclic aromatic halides have been studied mainly in view of their synthetic applications, and it is not always clear which mechanistic pathway is followed. The reaction may start with homolytic or heterolytic dissociation of the carbon-halogen bond and proceed by attack of the aryl radical or aryl cation on another part of the molecule. Electrocyclization followed by elimination of hydrogen halide is another possibility. Especially when heteroatoms such as nitrogen, sulphur or phosphorus are involved, the initial step may be a nucleophilic attack on the carbon atom bearing the halide atom. 

The base-promoted halogenation takes place by a nucleophilic attack of an enolate ion on the electrophilic halogen molecule. The products are the halogenated ketone and a halide ion. 

Nucleophilic displacement or halogen at C-2 or C-4 of quinoline, or at C-1 of isoquinoline, takes place readily halogens at other positions in these molecules are much more resistant to nucleophilic attack. Similar behavior is observed in halogenated thienopyridines. 

Step 2 Make a new bond between a w bond and an electrophile. Nucleophilic attack of the enol on the electrophilic halogen molecule, X, gives the conjugate acid of an a-haloketone. 

In comparision to 2-methyl-4-isothiazolin-3-one (15.1.), the antimicrobial activity of which bases merely on the availability of an activated N-S bond susceptible to nucleophilic attack, the 5-chloro-2-methyl-4-isothiazolin-3-one disposes additionally of a vinyl activated chloro atom and therefore can be characterized as a molecule with two toxophoric structural elements (Paulus, 1988). As a result CMI should exhibit stronger antimicrobial efficacy than the halogen-free MI. This is confirmed by examinations of Diehl and Chapman (1999) see Table 109. Applications for CMI are described under 15.3. 

The distribution of the electrostatic potential for two bromine species has further consequences particularly the location of the maxima of EP shows the most probable nucleophilic attacks here. This is why the liner halogen bonds are formed with BrFa while bent ones for the BrFs molecule. Figure 15.8 shows the molecular graph of the BrFa-NCH complex with the reactive surface corresponding to the laplacian of the electron density equal to zero. The straight bond path connecting the bromine atom with the nitrogen Lewis base center of HCN molecule is observed... 

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