Electrophilic means 'electron-loving'. An Electrophile is a chemical species that is electron-deficient. It will seek out an electron-rich site in an organic molecule.
Examples of electrophiles are: H+, Cl+, Br+, I+, NO2+, CH3+, CH3CO+, C6H5N2+.
The diagram below illustrates the initial attack of the Br+ electrophile on the benzene ring in an electrophilic substitution reaction. (The curly arrow shows the direction of movement of a pair of electrons.)
In addition to the electrophiles above which carry a full positive charge, some molecules, for example, Br2 and HBr, are electrophilic. Consider the ionic addition of bromine across the double bond of an alkene. This takes place readily when bromine dissolved in a non-polar solvent (e.g. tetrachloromethane) is added to an alkene such as ethene at room temperature in the absence of light.
The dipole is first induced in the bromine molecule before it approaches the alkene. Evidence for this is derived from the fact that the reaction does not take place if the bromine/tetrachloromethane solution is perfectly dry nor if the surface of the reaction vessel is coated with a non-polar material, e.g. paraffin wax.
Hydrogen bromide, generated by the action of concentrated sulphuric acid on sodium bromide, reacts rapidly with alkenes at room temperature yielding the halogenoalkane.
See also Nucleophile.