Mechanistic Basis for Markovnikovs Rule

Let s compare the carbocation intermediates for addition of a hydrogen halide (HX) to an unsymmetrical alkene of the type RCH=CH2 (a) according to Markovnikov s rule and (b) opposite to Markovnikov s rule. 

Higher energy transition state gives primary carbocation 

Energy diagrams comparing addition of a hydrogen halide HX with an alkene H2C=CHR according to Markovnikov s rule (solid red) and opposite to Markovnikov s rule (dashed blue). The energy of activation is less and the reaction is faster for the reaction that proceeds through the more stable secondary carbocation. 

Electron flow and orbital interactions in the transfer of a proton from a hydrogen halide to an alkene of the type H2C=CHR. 

Give a structural formula for the carbocation intermediate that leads to the major product in each of the reactions of Problem 6.4. 

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