Alcohol synthesis from Alkenes
Markovnikov’s rule
The electrophile adds preferentially to the sp2 carbon bonded to the most hydrogens
(that is, to the less substituted sp2 carbon).
- This rule will be the same as determining the relative carbocation stability.
- The electrophile (in this case, H +) adds preferentially to C-1 because it is the sp2 carbon bonded to the most hydrogens.
Alcohol synthesis via Hydration
- An alkene does not react with water,The OH bonds of water are too strong to allow the hydrogen to act as an electrophile.
- If an acid is added to the solution, then a reaction will occur because the acid provides the electrophile.
The protonated alcohol loses a proton because the pH of the solution is greater than the p Ka of the protonated alcohol.
Alcohol synthesis via Hydroboration–Oxidation
Boron (an electrophile) forms a bond with one sp2 carbon, it gives a hydride ion (a nucleophile) to the other sp2 carbon.
Hydroboration is an concerted reaction
- Because both the boron and the hydride ion are added to the alkene in a single step, no intermediate is formed and carbocation rearrangements do not occur.
Anti-Markovnikov Hydration
- The OH group ends up attached to the sp2 carbon bonded to the most hydrogens because it replaces boron, which was the electrophile in the hydroboration reaction.
9-BBN
- Only one hydride ion is needed for hydroboration. 9-BBN is often used instead of BH3.
- Since 9-BBN has two relatively bulky R groups, it has a stronger preference for the less substituted sp2 carbon than BH3 has.
