Ch 8 Ppt.
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What two reactions are direct opposites?
What is anti-Mark? What will cause anti-Mark reactions?
addition and elimination
a reactionin which the less-highly substituted product is formed
running the reaction in light or peroxide
Explain Markovnikov in terms of HBr
- Mark: adding HBr across the bond in carbocationic conditions leads to Mark
- anti: adding HBr in light and with a free radical initiator--> leads to a non-polar free radical mechanism (you know its anti-Mark when you run the rxn in the presence of organic peroxide and light)
What is crucial for substitution?
How can you test for the presence of an alkene? THis can also be done for __, which may be longer.
- leaving groups
- adding Br
Adding X-X across a bond is what? What will form?
What is not possible for this reaction? WHy?
Essentially, what kind of addition is this?
- trans is formed exclusively, no cis (enantiomers form)
rearrangement because bromine stabilizes it through becoming a bromonium ion and forcing the other bromine to come in through the opposite side
Even though these structures are asymmetrical carbons, what can't they be and why not?
cant be optically active because we are starting from optically inactive material
1) Types of addition:
- syn: coming in through the same face
- anti: coming in from opposite sides
only one stereoisomer is formed at the expense of the other (eg: cis vs. trans)
Explain the halohydrin reaction.
- anti-addition (trans is the product)
- water is the solvent and X2 is the reagent
since alkenes are insoluble in water, you need a phase transfer catalyst, creating regiospecific and stereospecific reactions
- the result will be the halogen on the less subbed and the -OH on the more subbed molecule
- the two adding groups are OH and a halogen
Catalytic hydrogenation results in what?
What is the catalyst?
What does the catalyst do?
- a syn addition
- a metal such as palladium or nickel
- the catalytic surface drives the reaction; the more fine the catalyst, the faster the reaction
What does hydrogenation do?
True or False:
Benzenes are not aleknes and don't react under alkene conditions.
reduce all the alkene pi bonds
What does hydration lead to?
Why is catalytic hydration catalytic?
- will occur with a hydrogen sulfate or phosphate
- mark addition
- first step: protonate
- second step: deprotonate
the catalyst (the acid in the rxn) is never consumed
- solvent and why
What can H do?
- - mercury metal
- - THF, which is an ether solvent that dissolves completely in water; because alkenes are insoluble in water but soluble in THF, it allows alkenes to become soluble in water--> one phase
- - H2O is a reagent
gain noble gas configuration--> H: --> hydride
- __ addition
- __ reaction
- what does it form as an intermediate?
- markovnikov addition
- regiospecific reaction
- mercurinium ion
- __ addition
- __ addition
- number of intermediates
- - adding water in opposite regiochemical position
- - anti-Mark
- - syn
- - none; just a transition state
Why does boron in hydroboration add to the less highly subbed?
- due to steric crowding
Regiochemistry is __. REgioselective is __.
- you'll probably get some of each, but you'll mostly get one
Explain syn fashion. anti.
Explain stereospecific in four words.
- must be cis to each other (the two arriving groups)
- trans must occur
cis and trans matter
What are the two complementary hydration reactions?
- hydroboration: the less highly subbed alcohol forms
- oxymercuration-demercuration: the more highly subbed alcohol forms
- what is involved
- what does it do
- what is the difficulty
- - carbene
- - carbene will be added across the double bond
- - lies in the angle strain--> super high energy
Why are cyclopropenes good electrophiles?
- electrophilic because they lack an octet
- nucleophilic because of the lone pair of electrons, which lie in an sp2 orbital
- they are super high energy and want to pop open
How do you form a carbene? (use trichloromethane as an example)
Strong base (like KOH or NaOH) abstracts the chloroform proton, leaving behind the electron pair from the CH bond and forming the, for example, trichloromethanide anion
Then, loss of a chloride ion and associated electrons from the C-Cl bonds yields the neutral dichlorocarbene
A carbene is similar to geometry of a __. There's a __ that is __ into which __.
- vacant p orbital
- low energy
- electrons can be received
- stereochemistry of an alkene will be __.
- If you want to get rid of Cl, what should you do?
- maintained in the product
- react it with Zinc dust to get the Cl off and replaced with H
Simmons- Smith reaction
- ___ in the presence of __ will form a complex and __ will be precipitated out, causing the equilibrium to shift towards __
What kind of addition is it?
Ozonolysis forms __ from an alkene.
__reaction: way of __ and converting to __.
- two carbonyl compounds
- cleaving C=C
O3 reacts with all __. As long as it's __. they would react.
If you had 4 carbonyls formed, what do you know?
If you had two carbonyls, you had what?
- alkene pi bonds
- you had 2 double bonds
- one double bond
What would you like to do?
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