Аннотация:The paper discusses the effect of the methoxy substituent and its position in the benzene ring of the molecule of benzotephum on the molecular, electronic structure, and biological activity. A comprehensive study by X-ray diffraction and quantum chemistry (DFT) methods allows us to study the relationship between the quantum-chemical parameters of the electronic structure and the antitumor activity of these compounds. The influence of the substituent on the reactivity of various fragments of molecules and on possible pathways of biotransformation of molecules is discussed.