Abstract When treated with concentrated nitric acid in dichloromethane at room temperature, the title compounds undergo an exclusive attack on the methyl group at the most crowded site, giving 6-acyl-2,3,4,5-tetramethylbenzyl nitrates, and 2,6-diacyl-3,4,5-trimethylbenzyl nitrates and/or (2,6-diacyl-3,4,5-trimethylphenyl)nitromethanes respectively, as the major products. While the predominant mode of the side-chain substitution reactions is nitrooxylation for acylpentamethylbenzenes and 1,3-dipivaloyl-2,4,5,6-tetramethylbenzene, it shifts to nitration for 1,3-bis(trihalogenoacetyl)-2,4,5,6-tetramethylbenzenes. Nitrodeacylation is seen to some extent for pivaloylbenzenes, but not for trihalogenoacetylbenzenes. The exclusive attack on the methyl group at the most hindered position can be explained by a sequence involving the attachment of a nitronium ion at the site meta to the acyl group, followed by a proton release from the resulting arenium ion to form a nitromethylenecyclohexadiene intermediate, which is then transformed into the benzylic compounds via a benzyl cation/nitrite anion pair.