Q.Which of the following reagents is helpful to differentiate ethylene dichloride and ethylidene chloride? a) Zn/methanol b) KOH/ethanol c) aqueous KOH d) ZnCl₂/Con.HCl

Poly halogen compounds carry two or more halogens, and the two commonest dihalide classes are distinguished purely by WHERE the two halogens sit on the carbon skeleton. gem-Dihalides ('geminal', same carbon): both halogens on ONE carbon, e.g. CH3-CHCl2 (ethylidene chloride/dichloride, 1,1-dichloroethane), made either from acetaldehyde + PCl5, or by adding HCl twice to acetylene via the vinyl chloride intermediate. vic-Dihalides ('vicinal', neighbouring carbons): the two halogens on ADJACENT carbons, e.g. ClCH2-CH2Cl (ethylene dichloride, 1,2-dichloroethane), made either by adding Cl2 directly to ethylene, or from ethylene glycol + PCl5/HCl. The single most exam-tested fact about this pair is how to tell them apart CHEMICALLY: both hydrolyse with aqueous NaOH/KOH, but a gem-dihalide gives an unstable geminal diol that collapses (loses water) to an ALDEHYDE OR KETONE, while a vic-dihalide gives a sta …