Sesquiterpene synthase converting farnesyl diphosphate to alpha copaene and delta-cadinene as the major products. (2E,6E)-farnesyl diphosphate = alpha-copaene + diphosphate (2E,6E)-farnesyl diphosphate = delta-cadinene + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.