Addition reactions of alkenes Flashcards
Addition reactions
Reactions with alkenes where the double bond is broken & forms 2 new sigma bonds (Addition of 2 groups)
Addition reactions are the reverse reactions of an ____________ reaction
Elimination reaction
Addition reaction is favored at ____________
Low Temp.
Elimination reaction are favored at ___________
High temp
Are addition reaction usually exothermic or endothermic?
Exothermic
Hydrohalogenation
An addition reaction that involves hydrogen & a halogen (HX, X= cl, br, or I)
In a hydrohalogenation reaction the H is placed on a position that already has alot of hydrogens & the halogen is placed on the more ______________
Substituted position
Markovnikov addition
When the H is placed on a position that has alot of hydrogens & when the halogen is placed on the more substituted position
Anti-Markovnikov reaction
The halogen is placed on the less substituted position & the H is placed on the side that doesnt have much hydrogens
When _______ reagents are used then the reaction will occur as markovnikov addition
Pure
When _______ reagent are used such as peroxides (ROOR) then it will occur as an anti- Markovnikov addition
Impure
What is the mechanism for hydrohalogenation?
- Proton Transfer
- Nucleophilic Attack
The regioselectivity for hydrohalogenation is what?
Markovnikov Addition
Hydrohalogenation products will have __________ centers where a pair of enantiomers will be observed
Chirality Center
Hydration
Addition of water (H & OH) across a double bond
Acid- Catalyzed Hydration
Addition of water across a double bond in the presence of an acid
The regiochemsitry of an Acid Catalyzed Hydration is what?
Markovnikov addition
What is the mechanism for an Acid - Catalyzed Hydration?
- Proton Transfer
- Nucleophilic Attack
- Proton Transfer
In an Acid - Catalyzed Hydration how do you control the position equilibrium?
Can control the position of equilibrium by controlling the amount of water present (Using either concerated or dilute acid)
What is the stereochemistry of Acid-Catalyzed Hydration?
The intermediate carbocation can be attack from either side so it forms a new chirality center & a racemic mixture of enantiomers
Oxymercuration - Demercuration
Addition of water (H & OH) across a double
Mercuric Acetate
Hg(OAc)2
When the double bond (π bond) is protonated in an oxymercuration - demercuration reaction what happens?
A carbocation intermediateis formed
When the double bond (π bond) is attacked by a mercuric cation what happens?
An Mercurinium ion is formed
The regiochemistry of an oxymercuration-demecuration is what?
A Markonvikov addition
Demercuration
Removal of mercury occurs by a radial reaction & results in the addition of H & a nucleophile (which is usually water
(H2O)
Hydroboration - Oxidation
Places the OH group on the less substituted position
What is the regiochemistry of an Hydroboration - Oxidation Reaction?
Anti- Markovnikov addition
What is the stereochemistry of a Hydroboration - oxidation reaction ?
Syn Addition (The prodcuts chirality centers have the H & OH on the same plane (Cis conformation))
If there is no chirality center formed in an hydroboration-oxidation reaction then what are the outcome of the products?
There will only be one product formed
When only one chirality center present in the products of an hydroboration - oxidation reaction then what is the outcome of the products?
Both enantiomers are observed
When there is two chirality center present in the products of an hydroboration reaction then what is the outcome of the products?
The chirality center are formed by a syn addition (So they are on the same plane) & a pair of enantiomer is observed
Catalytic Hydrogenation
Involves the addition of molecular hydrogen (H2) across a double in the presence of a metal catalyst
What is the stereochemistry of catalytic hydrogenation ?
When two new chirality center are formed then a pair of enantiomers are formed by a syn addition
What are the common heterogenous Catalyst in a catalytic hydrogenation reaction?
Pt, Pd, & Ni (They dont dissolve in a reaction)
What is the common homogeneous catalyst in a catalytic hydrogenation?
Wilkinson’s Catalyst (Rh(PPh3)3Cl)
Halogenation
Involves the addition of X2 (Either Br2 or Cl2) across an alkene
What is the regiochemistry of halogenation reaction?
Anti-Markonvikov addition
What is the stereochemistry of an halogenation reaction?
Anti Addition where the products will have the halogens on the opposite planes
In an Halohydrin reaction the OH is placed on what?
the more substituted position
What is the indications of a halohydrin reaction?
When you have a halogenation (either Br2 or Cl2) as a reagent & water as the solvent (Adds a halogen & OH across a double bond & the OH is placed on the more substituted position )
Dihydroxylation
Adding two OH
Halohyrin can make an epoxide through an ________ reaction
SN2
Ozonolysis Reaction
A reaction that cleaves the double bond ( The common reagents are DMS & ZN/H2O)
What do have consider when predicting the products of an addition reaction?
- What groups are being added across a double bond
- What is the expected regiochemistry (markovnikov addition or anti- markovnikov addition)
- What is the expected stereochemistry (Syn or Anti addition)
How do you change the position of a leaving group?
- Elimination reaction
- Addition reaction
How do you change the position of a double bond (π bond)?
- Addition reaction
2 Elimination reaction
