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Page 4
I- has a low charge density → Solvent will not cling to it very well, and
I- can easily break through the cage to attack an electrophile
I- (bigger atoms, down the column) will be most nucleophilic in polar
protic solvents since their solvent cage is weakest
Strong hydrogen bonding interactions stabilize charged species
Because F- interacts with the polar protic solvents most strongly, it will be most stabilized
Stabilization = less reactive
F- is also energetically stabilized and rendered less reactive in polar protic solvents
Charged nucleophiles used in polar aprotic solvents, nucleophilicity tracks with basicity
The most basic anion (F-) is most nucleophilic
Polar aprotic solvents cannot hydrogen bond
Don't interact with our nucleophiles
As a result, our most basic anion (F-) is not trapped in a solvent cage or energetically
stabilized in any way, leaving it free to roam about and quickly attack the electrophile
I- is very big and can distribute that negative charge over a large volume
I- will better stabilize its negative charge, making it less basic than F-
Neutral nucleophile → use polarizability (how easily the electron cloud distorts)
Bigger atoms (down a column) are more polarizable and more nucleophilic
SN1
Forms a trigonal planar sp
2
hybridized carbocation intermediate after the LG leaves
Carbocation intermediate is flat → both the top and bottom faces of the carbocation are
open for the nucleophile to attack
If SM contains stereocenters → we may generate two stereoisomers as products
If SM has no stereocenters → don’t worry about multiple stereoisomers and only
one unique product will be formed
E1
Zaitzev's rule (small bases)
Weak bases


Page 5
SN1 vs. E1
SN1 and E1 will occur simultaneously and a reaction that produces a carbocation will generate both SN1
and E1 products.
During the exam, pay attention to which mechanism I want you to focus on in each problem.
Carbocation rearrangements
Forming a carbocation → Risk for rearrangements and should check
adjacent positions only
to
determine if the molecule can be further stabilized
Adjacent positions are the only ones providing hyperconjugation stabilization and as a result are
the only ones that have the weakened sigma bonds
If a molecule can stabilize itself through a rearrangement, the molecule will rearrange; the
rearrangement will lead to the major product
Ways to stabilize the molecule include:
Forming a more stable carbocation through a
hydride or alkyl shift
Ring expansion
Only occur for 3, 4, and 5-membered cycloalkanes
Relieves angle strain in the very small rings
If you have a choice between a ring expansion or a shift, do the ring expansion first.
Reducing ring strain lowers the energy of the molecule significantly more than moving the
carbocation to a more substituted position


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