What Reaction coditions does Sn2 prefer?
Polar aprotic solvent
A solvent with NO H attached to highly electronegative atom
What reaction conditions does Sn1 prefer …
Polar Protic Solvent in cold conditions
If in hot conditions: E1
Describe the nucleophile in Sn2
A STRONG nucleophile, look if it is a strong base to assess Elim.
Nu in Sn1
Poor Nu, eg) alcohols, water, carboxylic acid, bulky Nu’s
What is the stereochem. of a Sn1 product?
Racemic mixture of enantiomers
1 of the pair my be prefered based on steric hinderance of the substrate
What is the stereochem of a Sn2 product
Inverted stereochem due to the backside attack mechanism
What is the best substrate for a Sn1 Reaction
LG attached to a 2’ or 3’ C (carbocation stability)
What is a good substrate for Sn2
methyl or 1’ leaving group connectivity
Explain the mechanism of Sn2
the Nu attacks at the back of the C attatched to the LG, the LG leaves.
all one step
Describe the mechanism of Sn1
The LG leaves. The Nu attacks the carbocation.
2 steps
I general, what slows a reaction?
Steric hinderance
What structural change do you have to look for in Sn1 AND E1?
Methyl and Hydride shifts to stabilize the intermediate carbocation
In general substitutions prefer the cold
true
What is the operation for assessing a Nu?
Look at basicity first (Elims) then nucleophilicity, then if E is an option look at bulkiness
Nucleophilicity increases …
to the left and down on the periodic table
Due to EN and polarizability respectively
The solvation shell is
the shell of PROTIC solvent molecules that hydrogen bond to the Nucleophile, slowing reaction
This is why Sn2 wants polar aprotic solvent
Larger Nu (I- compared to Br-) feel less effect from solvation
If the temp. condition of a Sn1 reation is not specified …
E1 will occur as well.
