Chapter 11: Addition Reactions Flashcards
What is the outcome of this reaction?
What is the regiochemistry of this molecule?
Markovnikov product/addition
What is the regiochemistry of this molecule?
Anti-markovnikov product/addition
What is the stereochemistry of this molecule?
Syn
What is the stereochemistry of this molecule?
Anti
What are the products of this reaction if they are Markovnikov and syn
What are the products of this reaction if they are anti-markovnikov and syn?
What are the products of this reaction if they are anti-markovnikov and anti?
What is the regiochemistry and stereochemistry of a H2 (H-H) addition reaction?
What is the outcome of this reaction?
Meso because there is a plane of symmetry
What is the outcome of this reaction?
Have to show D atoms
What is the outcome of this reaction?
results in enantiomers
What is the regiochemistry and stereochemistry of H-Halogen addition reactions?
What is the mechanism of H-Halogen addition reactions?
Carbocation forms on the more substituted carbon because it is more stable. The halogen then acts as a nucleophile to attack the carbocation forming a Markovnikov addition.
What is the mechanism of this H-Br addition reaction?
There is a carbocation rearrangement to stabilize the secondary carbocation, creating a tertiary carbocation. Br then acts as a nucleophile and attacks the tertiary carbocation, forming a markovnikov addition.
What is the mechanism of this H-Br addition reaction?
Alkyl migration occurs to make the secondary carbocation a tertiary carbocation so it is more stable.
What will cause a H-Halogen addition reaction to be anti-Markovnikov?
Adding peroxide (ROOR) as a reagent in the reaction
What is the mechanism when H-Halogen, ROOR are used in an addition reaction?
RO OR are broken homolytically (each oxygen keeps their shared electron) in the presence of light or heat. The radical RO obstructs H, H-Br bond breaks, forming radical Br which attacks the less substituted carbon so the radical can be transferred to the tertiary carbon (more stable). The radical tertiary carbon is then abstracts a H from H-Br to from an anti-markovnikov addition with 2 enantiomers.
What is the regiochemistry and stereochemistry of H and OH addition reactions?
What is the mechanism of this reaction?
Pi bond extracts H from H3O+ and the H-OH bond is broken to from a tertiary carbocation (more stable) plus water. H2O then acts as a nucleophile and attacks the tertiary carbocation. The new molecule formed has a + charge on H2O, so another H2O extracts an H forming an OH markovnikov addition.
Why are two arrows used in this reaction?
The reverse of the reaction is an E1 elimination reaction (H2O in the presence of acid creates a good LG)
What are the reagents used to make a H and OH addition reaction anti-markovnikov and syn?
What is the mechanism used to make a H and OH addition reaction anti-markovnikov and syn?
Borane (BH3) does not have an octet (empty p orbital but no positive charge) making it very reactive. The solvent THF can donate electron density into the empty p orbital of borane to help stabilize it. However, borane still looks for areas of electron density (in this case the Pi bond which attacks the empty p orbital of borane and triggers a hydride shift). Borane ends up on the less substituted carbon because it is bulkier and is sterically hindered. An oxidation reaction with H2O2 and NaOH then occurs that replaces the borane with OH (see page 196 in textbook)
What is the regiochemistry and stereochemistry of a Br2 (Br-Br) addition reaction?
What is the mechanism of this reaction?
A bromonium ion is formed and then attacked from behind by Br-, creating anti stereochemistry
How does a Bromonium ion form?
The Pi bond has an area of high electron density and when Br2 approaches it, the Pi bond repels the electron density of Br2 creating a temporary dipole. The electron dense Pi bond then attacks the electron poor bromine
What is the regiochemistry and stereochemistry of a Br and OH addition reaction?
Don’t use markovnikov/anti-markovnikov here because there is no H atom
What is the mechanism of this reaction?
Bromonium ion formed in the first step. H2O acts as the nucleophile and attacks the more substituted carbon because it acts as a carbocation and is more stable. The oxonium ion (H2O+) is then deprotonated by another water molecule to from OH.
What reagents are used to form an anti OH and OH addition reaction?
Peroxyacids (example: meta-chloroperbenzoic acid (MCPBA)) reacts with alkene to form an epoxide.
H3O+ (water under conditions of acid-catalysis) protonates the epoxide to form a + charged intermediate that is attacked by water from the back side (why it is anti). Water then acts as a base and removes a proton from the H2O+ to form anti OH and OH enantiomers. (see page 210)
Name the molecule
peroxyacid
Name the molecule
meta-choloroperbenzoic acid (MCPBA)
Name the molecule
peroxide
What reagents are used to form an syn OH and OH addition reaction?
Reaction is called syn dihydroxylation
H2O2
Osmium tetroxide (OsO4) adds across the alkene in a concerted process (both oxygen atoms attach to the alkene at the same time). This is why it results in syn stereochemistry.
The same process can occur with cold KMnO4 and hydroxide
What is this reaction?
ozonolysis (adding across alkene and completely cleaving the Pi bond)
What is the mechanism of ozonolysis
How to draw an ozonolysis reaction
