3chloro

3-chloro, written with a hyphen between the numbers and element, is a substituent descriptor used in organic chemistry to indicate that a chlorine atom is attached to the third carbon of the parent structure. It is part of systematic IUPAC naming conventions in which substituent positions are specified by locants to identify where the chlorine atom is bonded on the molecule.

In practice, the meaning of 3-chloro depends on the chosen parent framework. For a monocyclic aromatic ring like benzene, a single chlorine substituent would be named chlorobenzene rather than 3-chlorobenzene, but once a second substituent is present, the ring can be numbered so that the chlorine occupies position 3. In such cases, 3-chloro indicates a meta relationship relative to the other substituent(s). The shorthand 3-chloro is often contrasted with 2-chloro (ortho) and 4-chloro (para) to describe relative positions on the ring.

Common examples include 3-chlorotoluene (m-chlorotoluene), 3-chloroaniline, 3-chlorophenol, and 3-chloropyridine. These names reflect the chlorine’s placement on the respective parent structures and are used in both academic and industrial contexts to specify exact molecular topology.

Notes: the locant system extends beyond simple rings to other carbon frameworks, where 3-chloro similarly denotes a chlorine substituent on the third carbon from the chosen reference point. In chemical databases and literature, the chlorine atom is also represented as a substituent with the label Cl and a locant of 3 in the full name.