Addition Reactions Flashcards
Def hydrohalogenation
Adding H and X (Cl, Br or I) across a pi bond
Do addition reactions increase or decrease entropy?
Decrease ( two molecules go down to one)
When considering the regioselectivity of hydrohalogenation reactions, to which Carbon does the Hydrogen bond?
MARKOVNIKOV hydrogen atom bonds to vinylic carbon that already bears the most hydrogens
One way to observe the halogen bonded to the less substituted site would be to include what reagent?
ROOR peroxides
Stereochemistry of hydrohalogenation.
Racemate
Def hydration
Adding water
Why is it necessary to include an acid catalyst when hydrating a molecule?
?
If a scientist wants more of the Alkene than the alcohol should he use conc or dilute acid?
Conc acid means less water available so hydration doesn t occur as readily, favoring the alkene
How is oxymercuration demercuration different from simple acid catalyzed hydration?
REMEMBER! In both, there is a MARKOVNIKOV addition. Ie the hydroxyl group is added to the more substituted carbon. But in odemerc, alkene attacks mercuric cation not hydrogen. This means a rearrangement will not happen
Name three ways of hydrating alkenes
1- acid catalyzed H2SO4 or H3PO4
2- oxymercuration demercuration Hg(OAc)2, Nuc/ NaBH4
3- hydroboration oxidation
How does the oxymercuration demercuration reaction prevent rearrangement?
The intermediate is a mercurinium ion not a carbocation. The more substituted carbon (where HgOAc is NOT attached) has a partial positive but not a formal charge that would trigger a rearrangement. Instead, the Nuc attacks a partially positive carbon.
In oxymercuration demercuration reactions, why does the HgOAc (mercuric cation) bond to the less substituted carbon?
Hg atom is large (covalent radius is 132 pm whereas hydrogen’s covalent radius is 32 pm). Hg therefore would be unlikely to bond at the more substituted site due to steric hindrance
