The statement that halogens play a directing (ortho/para) and deactivating role in electrophilic aromatic substitution is a well-established foundational concept in organic chemistry and does not require citation.
The claim is a standard, textbook chemical fact regarding electrophilic aromatic substitution (EAS), classifying halogens as ortho/para-directing yet ring-deactivating groups due to the interplay of inductive withdrawal and resonance donation. None of the retrieved papers specifically target or debate this fundamental textbook rule, making it common knowledge in the context of chemistry education and principles.