The technical chlordane constituent designated compound K is a formal isomer of chlordane (C10H6Cl8) which is formed by chlorination of α-chlordene (1) (C10H6Cl6) via a Wagner-Meerwein rearrangement. Structural elucidation of K involves dechlorination reactions, especially spectroscopic studies (MS, 1H NMR, and 13C NMR) of various photodechlorination products (3-7). From these data a structure for compound K is proposed. Confirmation of this structure is obtained by single-crystal x-ray diffraction. According to the results, compound K corresponds to 2,4,4,5,6,6,7,8-octachlorooctahydro-1,5-ethenopentalene (2).