A direct density functional theory (DFT) calculation was performed for the formation of polychlorinated naphthalenes (PCNs) from dimerization of 4-chlorophenoxy radicals (4-CPR5) and cross-condensation of phenoxy radical (PhR) with 4-CPR, respectively. Several energetically feasible formation routes were proposed. The rate constants were computed by the canonical variational transition-state theory (CVT) with the small curvature tunneling (SCT) contribution over temperature range of 600-1200 K. This study shows that PCN productions from the dimerization of 4-CPR5 just contain DCNs. All the monochlorinated naphthalene (MCN) detected in the experiment from 4-chlorophenol (4-CP) as precursor are formed form the cross-condensation of PhR with 4-CPR. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.