DAT Ochem Substitution and Elimination Flashcards
an electron-rich species that tends to donate electron density
nucleophile
an electron-poor species or compound
electrophile
Nucleophile strength increases from…. on pd table
right to left
increase in nucleophilicity is due to decreasing
e/n
nucleophile strength increases down a group in what kind of solvent
polar protic
A larger
atomic radius results in
more reactive nucelophile
nucleophilicity decreases down a group in what kind of solvent
polar aprotic
In polar aprotic solvents, nucleophilicity parallels….
basicity
Basicity decreases
down a group
Both substitution and elimination reactions involve the
loss of LG
nucleophile attacks an electrophile and kicks out a leaving group… what kind of rxn
SN2
nucleophilic attack and loss of a leaving group occur in the same step.
concerted
rate law for sn2
k(nuc)(elec)
if a nucleophile attacks a chiral center, what happens to stereochemistry …. SN2
inverted
consists of separate steps and therefore is not concerted.
Sn1
first step of an SN1
carbocation intermediate formation via the loss of a leaving group.
what is the rate limiting step of an SN1 rxn
carbocation intermediate formation via the loss of a leaving group.
final step of SN1
nucleophilic attack of the carbocation.
SN1 can only occur with what kind of substrates
secondary and tertiary
rate law for SN1
k(electrophile)
Carbocations
can be stabilized by neighboring alkyl groups bonds via
hyperconjugation
what is the least stable carbocation rearrangement
vinyl
what is next to least stable carbocation rearrangement
phenyl
what is more stable carbocation, methyl or primary
primary
what is more stable methyl or phenyl
methyl
what is most stable carbocation arrangement
benzyl
what is next to most stable carbocation rearrangement
allyl
are SN1 reactions stereospecific
no
more substituted alkene,
zaitsev product
less substituted alkene
hofman
what product is favored if the base is large and sterically
hindered.
hofman
what product is favored When a
non-sterically hindered base is used
zaitsev
are E2 rxn concerted
yes
E2 rate law
k(base)(substrate)
In an E2 reaction, the leaving group and the beta proton must be
antiperiplanar
For cyclohexane, E2 reactions only occur if the leaving group and beta proton are
on adjacent axial
positions and are anti-periplanar to one another:
what version of alkene is preferred to be formed for an E2 rxn
E alkene
If the substrate has only one proton on the relevant beta carbon, only… (e2)
stereoisomer is possible
E1 rxn rate law
k(substrate)
E1 reactions occur using what kind of bases
weak
examples of weak bases
h2o or alcohol
strong bases favor…
e2 rxns over e1
Heat can be
added to the reaction to ensure that the
E1 product is favored over the SN1 product.
elimination of alcohols requires the use of
concentrated acid and heat
what is always the major product of an acid catalyzed dehydration reaction.
Zaitsev product
If the alcohol is primary, what type of rxn will occur
e2
The first step of acid catalyzed dehydration is…
protonation of the hydroxyl group to make it good lg
does not occur with a tertiary substrate,
SN2
what kind of rxns will a primary subs not work with
SN1, E1
which are possible with a secondary substrate,
all 4 mechanism
negatively charged molecule is
reactive, strong base/nucleophile
If the molecule is neutral and unreactive, it is a
weak base/nucleophile
A strong base/nucleophile will favor
SN2, E2
a weak base/
nucleophile will favor
SN1, E1
A sterically hindered molecule will almost
exclusively act as a
base
A polar protic solvent favors
E2
a polar aprotic solvent favors
SN2
At low temperatures, what is more likely
nucleophile subsititution
at high temps, what is more likely
elimination
Br-, I-, Cl-, H2S, RS-, HS-
non basic nucelphile
primary substrate, nonbasic nucleopuile
SN2
secondary subs, polar aprotic solv, nonbasic nuc
SN2
secondary subs, polar protic, nonbasic nuc
SN1
tertiary subs, non basic nucleophile
SN1
t-buOK, DBU, DBN,
Diisopropylethylamine,
Triethylamine, LDA, NaH
non nucleophilc base
what kind of rxn is favored for all non nucleophilc bases
e2
RO-: HO-, MeO-, EtO-
strong nuc, strong base
strong nuc, strong base, primary OR secondary, polar aprotic
SN2
strong nuc, strong base, primary OR secondary, polar protic
E2
strong nuc, strong base, tertiary
E2 only
ROH: HOH, MeOH,
EtOH
weak nuc, weak base
