acid-catalyzed cleavage of the intermediate metal di-ester formed during mno oxidation As you work through each of these sets of reactions, you should pay particular attention to the common features of the mechanisms in each group An understanding of a few basic chemical generalities will help you view reactions as broad classes, and help you avoid overt memorization The addition of halogen acids to alkenes is a stepwise process which generally involves a solvent-equilibrated carbocation intermediate. The formation of this intermediate is initiated through a simple acid-base equilibrium in which the halogen acid donates a proton to the alkene T-system, which is functioning as a Lewis base. The protonated T-system has a short lifetime and can rapidly revert to starting materials, or can rearrange from a(cationic) protonated T-bond, to an sp sigma bond adjacent to an sp carbocation center. If the alkene is unsymmetrical, the protonated -cloud intermediate can brea down by two pathways, as shown below, to potentially form carbocations having differing ground-state energies. The reaction pathways leading from this intermediate to the two carbocations will differ in energy, and, in general, the pathway leading to the more stable intermediate will be of lower energy, and will be the preferred pathway. Transition State for Formation of Primary Carbocation Transition State for Formation of More Stable Secondary Carbocation Ptotonated T-cloud The resulting carbocation is formed on the carbon of the alkene which is best able to stabilize the cationic center In simple unstrained non-conjugated systems, without adjacent heteroatoms, the order of stability of carbocations will be tertiary secondary primary. Since tertiary centers have no attached hydrogens, secondary centers have one and primary centers have two, there is an apparent inverse relationship between the number of attached hydrogens and the likelihood that the carbocation will form at that center This is theacid-catalyzed cleavage of the intermediate metal di-ester formed during MnO4 - oxidation. As you work through each of these sets of reactions, you should pay particular attention to the common features of the mechanisms in each group. An understanding of a few basic chemical generalities will help you view reactions as broad classes, and help you avoid overt memorization. The addition of halogen acids to alkenes is a stepwise process which generally involves a solvent-equilibrated carbocation intermediate. The formation of this intermediate is initiated through a simple acid-base equilibrium in which the halogen acid donates a proton to the alkene -system, which is functioning as a Lewis base. The protonated -system has a short lifetime and can rapidly revert to starting materials, or can rearrange from a (cationic) protonated -bond, to an sp3 sigma bond adjacent to an sp2 carbocation center. If the alkene is unsymmetrical, the protonated -cloud intermediate can break down by two pathways, as shown below, to potentially form carbocations having differing ground-state energies. The reaction pathways leading from this intermediate to the two carbocations will differ in energy, and, in general, the pathway leading to the more stable intermediate will be of lower energy, and will be the preferred pathway. The resulting carbocation is formed on the carbon of the alkene which is best able to stabilize the cationic center. In simple unstrained non-conjugated systems, without adjacent heteroatoms, the order of stability of carbocations will be tertiary > secondary > primary. Since tertiary centers have no attached hydrogens, secondary centers have one and primary centers have two, there is an apparent inverse relationship between the "number of attached hydrogens" and the likelihood that the carbocation will form at that center. This is the