A nucleophilic attack often occurs when an electron-rich species (the nucleophile) "attacks" an electron-deficient species (the electrophile, usually a carbocation), forming a new bond between the nucleophile and the carbocation.
Where does the nucleophilic attack in an sn2 mechanism?
A consequence of the concerted, bimolecular nature of the SN2 reaction is that the nucleophile must attack from the side of the molecule opposite to the leaving group. This geometry of reaction is called back side attack.
Where does an electrophile attack?
An electrophile is something which is attracted to electron-rich regions in other molecules or ions. Because it is attracted to a negative region, an electrophile must be something which carries either a full positive charge, or has a slight positive charge on it somewhere.
