A hydrogen atom joins to one of the carbon atoms originally in the double bond, and a halogen atom to the other. If HCl adds to an unsymmetrical alkene like propene, there are two possible ways it could add. Addition of HCl to Alkenes to Give Alkyl Chlorides by JAMES Description: Treatment of alkenes with hydrochloric acid (HCl) will result in the formation of alkyl chlorides. The chlorine always ends up at the more substituted carbon of the alkene, since protonation of the alkene will result … Electrophilic addition of HCl to alkenes The carbenium ion, which is formed by protonation of an alkene by HCl, is subsequently attacked by the chloride anion resulting in a monohalogenated alkane. The problem comes with the orientation of the addition - in other words, which way around the hydrogen and the halogen add across the double bond. Addition of HCl Addition of HCl definition: Treatment of alkenes with hydrogen chloride leads to the chloroalkanes. Addition to symmetrical alkenes. Orientation of addition. For example, with ethene and hydrogen chloride, you get chloroethane: With but-2-ene you get 2-chlorobutane: One of the most fundamental reactions in organic chemistry is the addition of HX to an alkene. This reaction is illusturated below, using the addition of HCl to ethylene as an example: Notice that ethylene is a symmetrical alkene: it has the same substituents (two … This reaction is called hydrochlorination. However, in cases where the alkene is unsymmetrical, regioselectivity in electrophilic additions is predicted by Markovnikov rule. Addition of HCl explained: It is very simple when the alkene is symmetrical. All alkenes undergo addition reactions with the hydrogen halides. For example, with ethene and hydrogen chloride, you get chloroethane: With but-2-ene you get 2-chlorobutane: Hydrogen halide addition to alkenes is a highly regioselective reactionbecause addition of the hydrogen halide across the double bond gives only one of the two possible con- stitutionally isomeric addition … However, in … Addition to symmetrical alkenes. What happens? A hydrogen atom joins to one of the carbon atoms originally in the double bond, and a halogen atom to the other. The reaction type is A + B → C, an addition reaction . All alkenes undergo addition reactions with the hydrogen halides.