Final answer:
IUPAC naming for aromatic compounds like dichlorobenzene and xylenes uses numerical positions or common prefixes (o-, m-, p-) to denote the arrangement of substituents on the benzene ring. The names include 1,2-dimethylbenzene (o-xylene), 1,3-dimethylbenzene (m-xylene), and 1,4-dimethylbenzene (p-xylene) based on the positions of the methyl groups.
Step-by-step explanation:
The IUPAC naming of compounds with substituents on a benzene ring is a systematic method of assigning names to organic compounds. Substituents on the aromatic ring are indicated by numbers, starting with 1 and continuing in a direction that gives the lowest possible numbers for the substituents. For example, with dichlorobenzene, the positions of the chlorine atoms can yield three different compounds: 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,4-dichlorobenzene, which can also be referred to using the common names ortho-dichlorobenzene (o-dichlorobenzene), meta-dichlorobenzene (m-dichlorobenzene), and para-dichlorobenzene (p-dichlorobenzene), respectively.
When naming dimethylbenzene, where the common name is xylene, if the methyl groups are adjacent, it is named o-xylene (1,2-dimethylbenzene). If the methyl groups are opposite, it receives the name p-xylene (1,4-dimethylbenzene). The name m-xylene applies to 1,3-dimethylbenzene, where the arrangement of methyl groups is neither adjacent nor opposite but in an intermediate position.
Step 4 in IUPAC naming emphasizes writing the name of the compound as a single word, by placing substituent groups first (in alphabetical order), followed by the parent name, and finally the family name. Hyphens are used to separate numbers from the names of substituents, and commas separate numbers from each other.