4chloro

4-chloro, sometimes written 4-chloro- or p-chloro, is a descriptor used in the systematic naming of organic compounds to indicate that a chlorine atom is attached to the fourth position of the parent structure, most commonly a benzene ring. In para-substituted systems, the reference point is the highest-priority group, giving a para relationship between the chlorine and that group. The term 4-chloro is not by itself a chemical; it is a position indicator in compound names.

Examples include 4-chloroaniline (p-chloroaniline), 4-chlorobenzaldehyde, 4-chlorotoluene, and 4-chlorophenol. These p-chloro derivatives are widely used as intermediates in organic synthesis and pharmaceutical development. The aryl chlorine bond can participate in cross-coupling reactions, such as Suzuki–Miyaura, Heck, and Sonogashira couplings, enabling the construction of carbon–carbon and carbon–heteroatom bonds.

In naming conventions, 4-chloro denotes a para relationship to a reference substituent on the same ring system, and the same principle applies to other ring frameworks where para positions are defined. While 4-chloro compounds are common in industry and research, they can be irritants or toxic; appropriate handling and disposal per safety data sheets is recommended.