Part of the oxygenase component of the chlorobenzene dioxygenase system that catalyzes the dihydroxylation of a range of aromatic compounds, including chlorinated benzenes and toluenes, and dinuclear aromatics such as biphenyl and dibenzo-p-dioxin (PubMed:9249026, PubMed:9791099, PubMed:11526005). The alpha subunit is responsible for substrate specificity (PubMed:9791099). chlorobenzene + H(+) + NADH + O2 = (1R,2R)-3-chlorocyclohexa-3,5-diene-1,2-diol + NAD(+) Binds 1 [2Fe-2S] cluster per subunit. Binds 1 Fe cation per subunit. Aromatic compound metabolism. This dioxygenase system consists of four proteins: the two subunits of the oxygenase component (TecA1 and TecA2), a ferredoxin (TecA3) and a ferredoxin reductase (TecA4). Belongs to the bacterial ring-hydroxylating dioxygenase alpha subunit family.