Q.Write IUPAC name of the compound drawn as structure i. — a cyclopentane ring whose one carbon bears both HO and CH₃:

The hydroxyl derivative of benzene is universally called phenol; its fully systematic IUPAC name is benzenol, though the shorter common name 'phenol' is itself IUPAC-accepted and used throughout in practice. When a second substituent is present, the common-name system uses the prefixes ortho (1,2-), meta (1,3-) and para (1,4-) to describe its relative ring position (e.g. o-cresol), while the IUPAC system instead uses plain numerical locants counted from the -OH-bearing carbon, which is always numbered C-1 (e.g. o-cresol becomes 2-methylphenol). The same locant convention extends to di- and trihydroxy phenols: catechol/benzene-1,2-diol, resorcinol/benzene-1,3-diol, and hydroquinone (quinol)/benzene-1,4-diol among the dihydroxy phenols; phloroglucinol/benzene-1,3,5-triol and pyrogallol/benzene-1,2,3-triol among the trihydroxy phenols.