click on the reactant for a short review on the stereochemistry and regiochemistry of the reaction.

The top and bottom carbons are both enantiomeric and the molecule does not contain an internal plane of symmetry, making the two products enantiomers.

The top and bottom carbons are both enantiomeric but the molecule contains an internal plane of symmetry, making the two products identical and meso.

The top and bottom carbons are both enantiomeric and the molecule does not contain an internal plane of symmetry, making the two products enantiomers.

The top and bottom carbons are both enantiomeric and the molecule does not contain an internal plane of symmetry, making the two products enantiomers.

The addition of bromine to an alkene involves an intermediate bromonium cation. The addition of bromide anion to this intermediate is from the opposite face, making the net addition trans. In this example, the alkene is symmetrical, hence there is no regioselectivity.

The oxidation of an alkene with alkaline permanganate produces an intermediate manganate diester, which rapidly breaks down to give the cis 1,2-diol (a glycol).

The addition of HOBr to an alkene involves the formation of an intermediate bromonium cation, identical to that observed in the addition of bromine. This bromonium ion reacts rapidly with hydroxide anion from the opposite face to give the trans adduct. In this example, the alkene is symmetrical, hence there is no regiochemistry, otherwise, the hydroxide will typically be bound to the carbon of the alkene which would form the most stable carbocation center (Markovnikov addition).

The reaction of al alkene with BH₃ in THF solvent proceeds by a concerted mechanism to add the boron and the hydrogen cis relative to each other. The regiochemistry is anti-Markovnikov (the hydrogen bonds to the carbon which would form the most stable carbocation center). Work-up with alkaline peroxide oxidizes the intermediate borane to the alcohol, with retention of stereochemistry at the borane carbon.