Polar Aprotic Solvents
F- > Cl- > Br- > I-
Nucleophilicity = Basicity
Solvates cations
Polar Protic Solvents
I- > Br- > Cl- > F-
Nucleophilicity /=/ Basicity
Solvates cations and anions
SN1 Reactions
- formation of a carbocation
- love polar protic solvents
- result in EQUAL mixture of stereoismers (R and S) racemic mixture
- 3 > 2 > 1 > CH3 (1 and CH3 do not do SN1 reactions)
SN1 Reaction Rate
only the concentration of the alkyl halide affects the reaction rate
rate = [alkyl halide]
SN2 Reactions
- backattack
- love polar aprotic solvents
- can result in inversion of configuration if reaction is on a chiral carbon (if not, config. is retained)
- CH3 > 1 > 2 > 3 (3 does not undergo SN2)
E1 and E2 Reaction
3 > 2 > 1
SN2 Reaction Rate
concentration of alkyl halide and nucleophile affects reaction rate
[alkyl halide][Nu]
Examples of polar protic solvents
H20, MeoH, EtOH, acetic acid, ammonia
(contains a Hydrogen)
Examples of polar aprotic solvents
DMSO, DMF, acetone, acetonitrile, CN-, I-
Elimination is favored when
- using a strong base (pka > 14) and has a negative charge
- high temperature
- 2 or 3 alkyl halide
- using a strong, bulky base such as isopropyide or tert-butoxide
Zaitsev's Rule
formation of the most substituted alkene is favored with a small base
this is because the most substituted alkene is the most stable
most stable -> major product
E2 reactions on cyclic molecules
must be anti-coplanar
Cis formations on cyclic molecules yield how many products
2
Trans formations on cyclic molecules yield how many products
1
True/False
Trans alkenes are more stable than cis alkenes
True
when 2 alkenes can be formed, the most substituted will predominate when...
a strong unhindered base is used
when 2 alkenes can be formed, the least substituted will predominate when...
a strong, bulky base is used
when substituents are all facing up, the molecule is...
cis
when one substituent is facing up and the other is facing down, the molecule is...
trans
the halogen must be _____ in order to react with a labile hydrogen.
anti-coplanar
What kind of reagent would you use to eliminate a halogen?
A strong, bulky base
Basicity is a ____ matter
thermodynamic
Nucleophilicity is a _____ matter
kinetics
Regioselectivity
When more than one constitutional isomer is produced and one predominates
Stereoselectivity
When more than one stereoisomer is produced and one predominates
E ( entegegen)
when heaviest groups are on opposite sides of the plane
(based on atomic weight)
Z (Zusamenn)
when heaviest groups are on the same side of the plane
(atomic weight)
the most substituted has the ...
lowest heat of hydrogenation