fun facts 2 Flashcards
E2 general scheme
1 step
base attacks H
double bond forms
rate law for E2
bimolecular elimination
rate : k (subs) (base)
free energy diagram for E2
one hill
sm (2)
transition state (dotted line )
products (3)
unique thing about E2 reactions
stereo electronic requirement
H removed must be anti peri planar (think of waterfall in AS + newman projection, must be on beta carbon and pointing 180 away) - staggered anti conformation
why is e2 stereo electronic
to allow zaitzefs product : more substituted alkene
so the CH sigma bond is parallel to empty C -LG sigma star orbital
less energy in newman projection if they’re spaced out
what do big bases like t-BuO- do to e2 reactions
form the hoffman product
less substituted alkene
cant get to the anti peri planar H due to steric hinderance
what isomer is usually favoured in e2
e isomer ( diff sides)
then z isomer
then hoffman product
how is e2 stereospecific
diff diastereomers form diff isomers
eg : 1 makes E, 1 makes Z
e2 and stereoelectronic with benzene and chairs
normally if groups are equatorial, there is no antiperi planar H.
the groups must be axial
what type of substrate do E2 reactions prefer
3 will never happen with methyl subs
e2 and sn2 fight :
tertiary subs
NaOMe
Acetone
E2 only
e2 and sn2 fight:
2 subs
NaOMe
acetone
mostly sn2
a lot of e2 aswell
e2 cheat sheet
1 step
stereo electric
stereospecific
3, allylic, benzylic subs
strong bronsted lowry base
wide range of solvent
good lg
strong bronsted lowry bases for e2
RO-
R2N-
H-
t-BuO-
E1 reaction general scheme
loss of lg
cc+
attack of H
double bond formed
