Ch 6 Notes Pt. 1
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. What would you like to do?
What are the second order reactions?
What are some good leaving groups? Bad ones and why?
Bromine adn iodine are good, as well as chlorine
Fluorine is a bad leaving group because it holds its electrons tightly
What happens to the tetrahedron in SN2 reactions?
gets inverted because the nucleophile must approach the elctron 180 degrees behind the leaving group.
What does the transition state of the second order reaction rates look like?
one bond is forming and the other is leaving
What are SN1 and E1 only dependent on?
the substrate's concentration, not on the nucleophile
What can you not do with --OH?
What can you do with alcohols?
What is acetate? Tosylate?
doesn't act as a leaving group; you can't kick it out. You can convert it to something that will leave
convert alcohols into tosillates
good leaving group
Since the energy of the transition state is significant in determining __, a __ will react more rapidly than __ (which is much more rapid than __).
If there's room __ behind the leaving group, what should happen?
- the rate of the reaction
- primary substrate
- 180 degrees
- the reaction should go quickly
If there's no space on the substrate, what can't you do? What will happen?
When will this occur?
- you can't substitute
- you either eliminate or there will be no reactin
in tertiary halides or if the nucleophile is too bulky; it will become E2 if there's no space
For E2, space is not a oncern
What is protic? When don't we want this?
What are some protic examples?
__ should be able to __.
What do polar, protic solvents do?
- it can hydrogen bond
- in SN2 reactions
ethanol, methanol, H2O, etc.
polar, aprotic solvents; cage the metal cation
lower the energy of nucleophile
We can think of the nucleophile as a __; so, we need a strong solvent to have what happen?
- get the nucleophile to break into its ions
Tendency of a substance to behave as a nucleophile:
- strength parallels what? ex?
If you have too strong a base, what will happen?
What do we want for SN2?
- base strength; F is a weak base and even weaker nucleophile; Oh is both a strong base and a strong nucleophile
a good base that isn't strong enough to pluck
Nucleophile strength roughly parallels ___.
Nucleophile strength increases __.
A base is always a stronger nucleophile than __.
Both NH2- and NH3 can act as nucleophiles; what is the only difference?
going down a group
its conjugate acid
the one with the negative is a stronger BL base
Good leaving groups are __.
The C- LG (leaving group) bond is broken during __. What is crucial?
What is a group of excellent LGs?
The better the leaving group, what?
- weak bases
- quality of leaving groups
- the faster the rate occurs
__ are easily prepared from alcohols.
__ can be good leaving groups. They can be easy to spot.
What is the only requirement?
- neutral molecules
- has to be on a saturated center
In a bimolecular elimination (E2), what does the nucleophile act as?
If the substrate is too congested, what doesn't happen? Why not?
- a bronsted base
- SN2; has more steric issues
Which reactions compete?
- What does it depend on?
- What are good bases?
Good nucleophiles lead to __.
Bases prefer to __.
- Sn2 vs. E2
- Sn1 vs. E1
- the nature of the nucleophile
Sn2 competes with E2
- What are the guidelines for determining?
- - size of the base
- ---> bulky= E2
- - nature of the substrate
- ---> strong nucleophile, weak base= Sn2
A strong nucleophile with primary carbons go through __.
What are Sn2 conditions?
- polar aprotic; low temp; good nucleophile
What is a Beta carbon? What does it apply to?
What does coplanar mean?
- the carbon that is adjacent to the carbon carrying the leaving group; it produces an anti configuration
- SUBSTRATE MUST BE ANTI TO ONE ANOTHER
In a cyclohexane, the leaving group must be __.
What is Zaitsev's rule?
in an elimination reaction, the more highly substituted alkene (usually) predominates
What is hyperconjugation?
The more overlap that occurs, what?
a pi bond associates with adjacent C-H antibonding bond
the lower the energy becomes
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