A-Level Substitution and elimination in halogen compounds: worked solution

Question

Groundwater found to be contaminated with TCE was examined. Analysis revealed three further chlorine-containing organic compounds in the sample. Propose structures for these three compounds.

TCE is trichloroethene, Cl2C=CHCl. Replacing one chlorine atom by hydrogen (partial dechlorination) gives dichloroethene, C2H2Cl2, which exists as three isomers. Removing the lone Cl from the CHCl carbon gives 1,1-dichloroethene (CH2=CCl2); removing one Cl from the CCl2 carbon gives 1,2-dichloroethene, which occurs as geometric cis and trans forms.