Regiospecificity of Hydrogen Halide Addition

Two products could conceivably result from the addition of HBr to an unsymmetrical alkene, but only one is formed. For example, addition of HBr to propene could yield either 1-bromopropane or 2-bromopropane, but only the latter forms. Thus, the addition of an HBr to an alkene is teglospe-Hfic. 

In 1870, the Russian chemist Vladimir Markovnikov observed that reagents add to imsymmetrical alkenes in a specific way. Markovnikov s rule states that a molecule of the general formula HX adds to a double bond so that the hydrogen atom forms a bond to the unsaturated carbon atom with the largest number of directly bonded hydrogen atoms. This is the less substimted double-bonded carbon atom. The addition reactions of HCl with 2-methylpropene and 1-methylcyclohexene with HBr are two examples of Markovnikov s rule. 

Predict the product(s) formed when HCl adds to each of the following. 

Compound I is l-metliylq clooctene. One hydrogen atom is bonded at C-2 and none at C-1. Thus, hydrogen adds at C-2 and bromine at C-1. Compound II is methylenecyclooctene. There are two hydrogen atoms at the methylene carbon and none at C-1. Thus, hydrogen adds at the methylene carbon atom and bromine adds at C-1. The product, 1-bromo-l-methylcyclooctane, is the same for both compounds. 

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