The nitration of p-cresol by nitric acid in aqueous sulphuric acid involves ~40% ipso-substitution at CMe. The 4-methyl-4-nitrocyclohexa-2,5-dien-1-one (I) formed undergoes an acid-catalysed rearrangement to 4-methyl-2-nitrophenol.

In the quantitative mononitration of anisole in 54–82% sulphuric acid at 25° the o : p ratio varies from 1.8 to 0.7. It is suggested that the rate-limiting step is the formation of an encounter pair between the nitronium ion and an anisole molecule which is hydrogen-bonded to a hydronium ion. The change in the o : p ratio may be due to competition between direct formation of Wheland intermediates from the hydrogen-bonded encounter pair, and loss of the hydronium ion to give a nitroniurn ion–anisole encounter pair, with subsequent formation of Wheland intermediates. With o- and p-methylanisole the products, and changes in product ratios with acidity are interpreted by considering the fates of the ipso-Wheland intermediates formed at C–Me. 4-Methyl-2-nitrophenol is an important product of the nitration of p-methylanisole, and results from ipso-attack by nitronium at C–Me, followed by attack of water and loss of methoxy.