An electrophile is any compound or reaction intermediate that is electron-deficient and thus accepts electrons from another source. The word electrophile is derived from the Greek words electros meaning electron, and philos meaning loving. Coined by Sir Christopher Ingold, the common notation used by chemists to represent an electrophile is E+, where E stand for the electrophile and the positive sign emphasizes its electron deficiency.

However, electrophiles can be neutral, partially positively charged, or have a full positive charge. Some examples of positively charged electrophiles are the hydronium ion, nitronium ions, metal ions, and carbocations. Some examples of neutral electrophiles are ozone (O₃), Lewis acids (such as BF₃), sulfonating agents, halogenating agents (such as Cl₂), and peracids. Electrophiles can also be reaction intermediates that do not have an octet of valence electrons, such as carbenes, nitrenium ions, and halogen atoms. Ingold was among the earliest chemists to recognize...