Boron contains three electrons in its valence shell (atomic number 5).

• Boron utilizes sp2 hybrid orbitals to form bonds with three additional atoms.

• Boron's vacant 2p orbital is perpendicular to the plane formed by boron and the other three atoms to which it is bound.

• Boron trifluoride: BF3, is a planar molecule with F-B-F bond angles of 120° that is an example of a stable trivalent boron compound (as shown in the image attached).

• Because of the unoccupied 2p orbital in the boron's valence shell, BH3, BF3, and all other trivalent boron compounds are electrophiles.

These boron compounds are similar to carbocations, but unlike carbocations, they are electrically neutral. BH3 is a planar molecule with 120° H-B-H bond angles (as shown in the image attached).

• In the image attached, (a) cartoon and (b) calculated orbitals and bond angles BH3

If there are electrons on the right side of the balanced half-reaction, the reactant gives up electrons and is oxidized.

If electrons occur on the left side of a balanced half-reaction, this indicates that the reactant has gained electrons and is reduced. If there are no electrons in the balanced half-reaction, the transformation is neither oxidation or reduction.

• Syn stereoselective: refers to the addition of atoms or a group of atoms to the same face of a carbon-carbon double bond.

The production of a cyclic osmate in such a way that the five-membered osmium-containing ring is bound in a cis configuration to the initial alkene accounts for the syn stereoselectivity of the osmium tetroxide oxidation of an alkene.

• Osmates can be separated and studied.

• Typically, the osmate is directly treated with a reducing agent, such as NaHSO3, which cleaves the osmium-oxygen bonds, yielding cis glycol and reduced forms of osmium.

• The disadvantages of OsO4 are that it is both costly and very poisonous.

To avoid the high expense, use it in catalytic proportions in conjunction with a stoichiometric quantity of another oxidizing agent whose goal is to reoxidize the reduced forms of osmium and therefore recycle the osmium reagent.

Hydrogen peroxide and tert butyl hydroperoxide are two secondary oxidizing agents that are often utilized for this purpose.

• There is no need for a lowering step with NaHSO3 when utilizing this approach, as shown in the image attached above.

• The treatment of an alkene with ozone, O3, followed by an appropriate work-up, cleaves the carbon-carbon double bond and generates two carbonyl (C"O) groups in its stead. O3, like all of the reagents mentioned in this chapter, is extremely electrophilic. This reaction is notable since it is one of the few organic reactions that destroys C!C bonds.

The alkene is dissolved in an inert solvent, such as CH2Cl2, and an ozone stream is bubbled through the solution.

• The products extracted from ozonolysis are determined by the reaction circumstances. Hydrolysis of the reaction mixture with water produces hydrogen peroxide, an oxidizing agent capable of causing additional oxidations.

To avoid side reactions produced by reactive peroxide intermediates, a mild reducing agent, most frequently dimethyl sulfide, (CH3)2S, is utilized.