Chapter 8 - Mechanisms Flashcards
What is the reaction for Hydrohalogenation?
R−CH=CH2 + HBr → R−CHBr−CH3
This represents Markovnikov addition.
What is the first step in the Hydrohalogenation mechanism?
Protonation of the Alkene
The π-bond of the alkene acts as a nucleophile and attacks the proton (H+) from HBr.
What occurs during the Nucleophilic Attack in Hydrohalogenation?
The bromide ion (Br−) attacks the carbocation, forming the final product.
How does the presence of peroxides affect Hydrohalogenation?
A radical mechanism occurs where Br adds to the less substituted carbon (Anti-Markovnikov).
What is the reaction for Acid-Catalyzed Hydration?
R−CH=CH2 + H2O/H2SO4 → R−CHOH−CH3
This represents Markovnikov addition.
What is the initial step in the Acid-Catalyzed Hydration mechanism?
Protonation of the Alkene.
What does water do during the Nucleophilic Attack in Acid-Catalyzed Hydration?
Water (H2O) attacks the carbocation, forming an oxonium ion (R−CHOH2+).
What happens during the Deprotonation step in Acid-Catalyzed Hydration?
Another water molecule deprotonates the oxonium ion to form the alcohol.
What is a key note regarding carbocation in Acid-Catalyzed Hydration?
Carbocation rearrangements are possible if a more stable carbocation can form.
What is the reaction for Oxymercuration-Demercuration?
R−CH=CH2 + Hg(OAc)2, H2O/NaBH4 → R−CHOH−CH3
This represents Markovnikov addition without rearrangements.
What is formed in the first step of the Oxymercuration mechanism?
Formation of the Mercurinium Ion.
What occurs during the Nucleophilic Attack in Oxymercuration?
Water attacks the more substituted carbon, breaking the three-membered ring.
What is the final step in the Oxymercuration-Demercuration mechanism?
Sodium borohydride (NaBH4) replaces the mercury with a hydrogen atom.
What is the reaction for Hydroboration-Oxidation?
R−CH=CH2 + BH3⋅THF/H2O2, NaOH → R−CH2−CH2OH
This represents Anti-Markovnikov, syn addition.
What happens during Hydroboration?
Borane (BH3) adds across the double bond with boron attaching to the less substituted carbon.