Electrophiles Electron-poor reactants strong electrophile

Novv, what about the second reactant, HBr As a strong acid, HBr is a powerful proton (H ) donor. Since a proton is positively charged and electron-poor, it is a good electrophile. Thus, the reaction between HBr and ethylene is a typical electrophile-nucleophile combination, characteristic of all polar reactions. 

The kinetics of addition of nitrosyl chloride to a number of olefins have been examined. In chloroform, methyl and phenyl substituents enhance the rate while electron-withdrawing groups (e.g. chlorine) retard it. Such be-haviour would be consistent with electrophilic attack by the dipole NO-CP. The effect of changes in the solvent was not simple, although more polar solvents (nitrobenzene, chloroform) speeded the reaction (compared with toluene or carbon tetrachloride). Methanol appeared to be a remarkably poor reaction medium, perhaps due to interaction with the reactant the low reactivity of nitrosyl chloride in diethyl ether was attributed to strong bonding between the solvent and the incipient NO cation. 

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