3-Chlorobenzo [b] thiophene-2-carbonyl chloride was synthesised from cinnamic acid and thionyl chloride. The single crystal X-ray structure determination confirmed the earlier proposed structure and the product was further characterised by 1H NMR, 13CNMR and mass spectrometry. The X-ray structure determination revealed two sets of symmetry related molecules along the b-axis that are loosely connected by relatively weak CH… π (3.626, ...