The core structure is a benzothiophene, consisting of a benzene ring fused to a thiophene (a five-membered aromatic ring with one sulfur atom). The sulfur atom is adjacent to both ring junctions.

Number the bicyclic system by IUPAC convention: the sulfur atom of the thiophene is position 1; the two thiophene carbons that are not shared with the benzene are positions 2 and 3; the benzene bridge-head carbons are 3a (adjacent to C-3) and 7a (adjacent to S); moving from 3a around the benzene ring gives positions 4, 5, 6 and 7 in sequence, returning to 7a.

Substituents:
- Position 5 (on the benzene ring, para to 7a) bears a chloromethyl group (-CH2Cl).  
- Positions 6 and 7 each carry a chlorine atom.