Hydroxyl groups addition across double bonds

Hydroxylation, the addition of two hydroxyl groups across double bonds, converts alkenes and cycloalkenes into vicinal dials. Stereochem-ically. the addition may occur in the syn or the anti mode. In open-chain alkenes (with the exception of terminal alkenes for which stereochemistry is irrelevant), syn hydroxylation transforms cis alkenes into erythro (or meso) diols and trans alkenes into threo (or dl) diols. anti Hydroxylation of cis alkenes gives threo (or dl) diols, whereas anti hydroxylation of trans alkenes yields erythro (or meso) diols. syn Hydroxylation of cycloalkenes gives cis diols, whereas anti hydroxylation furnishes trans diols (Table I). 

Hydroxylation, the addition of two hydroxyl groups across a double bond, converts fluonnated alkenes to different products depending on the presence or absence of a fluorine atom at the hydroxylated carbon... 

Alkenes get converted to alcohols by treatment with aqueous acid (sulphuric or phosphoric acid (Following fig.)). This electrophilic addition reaction involves the addition of water across the double bond. The hydrogen adds to one carbon while a hydroxyl group adds to the other carbon. 

The syn addition of BH3 across the double bond of norbornene takes place mostly from the more accessible outside (exo) face of the double bond. Oxidation gives a product with both the hydrogen atom and the hydroxyl group in exo positions. (The less accessible inner face of the double bond is called the endo face.)... 

Nakamura reported that the ultrasound-promoted reaction of tin hydride with alkenes in the presence of air results in the addition of stannyl and hydroxyl groups across the double bond (hydroxystannylation) (Scheme 16). This procedure is the first example of the conversion of alkenes to hydroxylated organotin compounds... 

These methods for adding water across a double or triple bond involve cationic intermediates, and always end up putting the new hydroxyl group at the position best able to stabilize a positive charge (see p. 433). By what about addition of water the other way round How would you do the reaction in the margin for example ... 

Addition of water across the carbon—carbon double bond, to yield a hydroxyl group. 

We saw earlier that halogens add across the double bond of an alkene to give l,2-dihalo compounds. In this section, we will consider the addition of chlorine, bromine, and bromine in water, a reaction that produces a halohydrin that is, a compound with a halogen on one carbon and an hydroxyl group on the adjacent carbon. 

In addition to direct hydroxylation by means of oxygen, a hydroxy group can also be inserted into a molecule by the addition of a molecule of water across a double bond. Actually that is the more common way and in the degradation of carbon chains it is invariably employed. 

---