There are still gaps in the theory of supposedly well-known chemical reactions. For example, there is no explanation why there is a notorious preponderance of one of the expected isomers in some electrophilic aromatic substitutions. The preferred ortho orientation of acetyl nitrate has been used widely to obtain ortho nitro compounds; however, there is not causal explanation of this phenomenon. In this communication, an explanatory discussion is given to provide a complete theory on the regiochemistry of some of the mentioned reactions. To illustrate our theory, acetanilide, toluene, and anisole have been chosen as substrates in nitrations performed with nitric/sulfuric acid mixture and with acetyl nitrate. (Contains 4 schemes and 3 figures.)