When benzene is substituted by halogens, which halogen gets position 1 in naming the compound?

In organic chemistry, when more than one halogen atom is attached to a benzene ring, the naming of the compound follows IUPAC rules based on the priority order of halogens and the alphabetical sequence of substituents. The position number “1” in the name is assigned to the substituent that appears first according to this order.

Among halogens—fluorine, chlorine, bromine, and iodine—fluorine is assigned the first position in naming because it comes first alphabetically. The IUPAC system always uses the rule that, when two or more different substituents are present on a benzene ring, the one that appears first in alphabetical order gets the lowest possible locant and is written first in the compound’s name.

For example, if both fluorine and chlorine are attached to the benzene ring, the compound is named 1-fluoro-2-chlorobenzene, not 1-chloro-2-fluorobenzene, because fluorine precedes chlorine alphabetically. This rule ensures consistency and clarity in chemical nomenclature.

Fluorine, due to its high electronegativity, also influences the ring’s reactivity and orientation of further substitution. In electrophilic substitution reactions, halogens act as deactivating but ortho-para directing groups due to their ability to donate electron density through resonance and withdraw it inductively.

Halobenzenes are an important class of aromatic compounds, serving as intermediates in the preparation of dyes, pharmaceuticals, and polymers. Understanding the correct naming and positional numbering of substituents is essential for accurate chemical communication and structural identification.

Therefore, according to the IUPAC naming convention and alphabetical precedence, fluorine always receives position 1 when benzene is substituted by multiple halogens