Carbocation Rearrangements Flashcards
Hydride
H with 2 e-
Why are there carbocation rearrangements?
To increase stability
What is more stable, more or less substituents? Why?
More bc of hyperconjugation
Hydride Shift Steps - SN1
(1) LG leaves
(2) reagent (Nu) attacks carbocation
(3) base deprotonates Nu to get rid of + charge
Hydride Shift Steps - E1
(1) LG leaves
(2) methyl shifts to the location of carbocation (which moves the carbocation)
(3) weak base deprotonates the new location of carbocation
Methyl Shift Steps
(1) look for LG & then look for nearby methyl groups
(2) swap methyl groups
How do you know which methyl to rotate in methyl shift?
Look at methyls close to LG & if multiple attached to same C, can rotate either bc of sigma bond
What is the goal of a methyl shift?
To get to tertiary alkyl halide bc the extra methyl increases stability
What is the most stable type of ring?
6-membered (as opposed to 5 or 4 or lower)
When can you do E1/SN1 for shifts?
Usually can do either
When wouldn’t you be able to do a hydride shift?
When there is no H between the beta and alpha
Torsional Strain
Caused by eclipsed bonds
When is a ring most stable?
When it reduces angle strain (which means it is closest to the ideal 109.5 degrees
What do you need to do an elimination w/ an alkyl halide?
Base
What do you need to do an elimination w/ an alcohol?
Acid
