Most aromatic compounds are named as substituted benzenes: the substituent is written as a prefix in front of benzene.• C6H5Cl is chlorobenzene, C6H5Br is bromobenzene
• C6H5NO2 is nitrobenzene
• C6H5CH3 is methylbenzeneSometimes the benzene ring is treated as a substituent on something else. The C6H5 group is then called the phenyl group. This happens with amines and ketones, and with the alcohol group:• C6H5NH2 is phenylamine
• C6H5COCH3 is phenylethanone
• C6H5OH is phenol
• C6H5COOH is benzoic acid (a common exception to learn)More than one substituent. Number the ring carbons 1 to 6 so that the substituents get the lowest possible numbers, and use di- or tri- for repeated groups. Groups are listed in alphabetical order. If one group gives the compound its parent name (such as COOH in benzoic acid or OH in phenol), its carbon is number 1.Worked example: a benzene ring carries two nitro groups with one carbon between them. Numbering from one nitro group gives positions 1 and 3 (not 1 and 5), so the name is 1,3-dinitrobenzene. Similarly, a ring with COOH and an OH on the next carbon is 2-hydroxybenzoic acid, and a ring with chlorine atoms on opposite carbons is 1,4-dichlorobenzene.
• C6H5NO2 is nitrobenzene
• C6H5CH3 is methylbenzeneSometimes the benzene ring is treated as a substituent on something else. The C6H5 group is then called the phenyl group. This happens with amines and ketones, and with the alcohol group:• C6H5NH2 is phenylamine
• C6H5COCH3 is phenylethanone
• C6H5OH is phenol
• C6H5COOH is benzoic acid (a common exception to learn)More than one substituent. Number the ring carbons 1 to 6 so that the substituents get the lowest possible numbers, and use di- or tri- for repeated groups. Groups are listed in alphabetical order. If one group gives the compound its parent name (such as COOH in benzoic acid or OH in phenol), its carbon is number 1.Worked example: a benzene ring carries two nitro groups with one carbon between them. Numbering from one nitro group gives positions 1 and 3 (not 1 and 5), so the name is 1,3-dinitrobenzene. Similarly, a ring with COOH and an OH on the next carbon is 2-hydroxybenzoic acid, and a ring with chlorine atoms on opposite carbons is 1,4-dichlorobenzene.