reactions of alkyl halides-g
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Alkyl Halides
Lecture Notes
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Cl
Cl
Cl
Cl
Br
12345
1
2
34
5
F
6
OH
I
CHCl3CH2Cl2
CCl3FFreon-11
CCl2F2Freon-12
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SN aliphatic & E are competing reactions
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Br
+ CH3CH2O-Na
+
OCH2CH3
Na+Br
-
+
+
+ CH3CH2O H Br-
Na+
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Kinetics
Reactivity of the RX
Structure of the Nucleophile Leaving Group
Stereochemistry
Solvent
Competing Reaction
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Strength of
nucleophile has
NO EFFECT
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Retension & inversion of configuration
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SN1: PROTIC SOLVENTS
- containOH groups and are H-
bond donors
- H2O, HCOOH, MeOH, EtOH, HOAc
- aid in ionization of C-X bond to
give X- & C+
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SN2: APROTIC SOLVENTS
- do not contain OH groups and
cannot function as H-bond donors
- DMSO, Acetone, DCM, Ether
- solvate only cations
- allow for highly reactive anions as
Nu-
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- Elimination Reactions
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Major products in eliminations are the alkenes
that are thermodynamically most stable.
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Rate=k[RX][base]
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Rate=k[RX]
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Primary
Does not occur
(unstable
carbocation)
Favored
Secondary &
Tertiary
Main reaction with
weak bases such
as H2O & ROH
Main reaction with
strong bases such
as OH- & RO-
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Cl
+ NaOH80oC
H2O[1]
Cl[2]
CH3COOH
[3]
Cl
+ CH3CH2O-Na
+
EtOH
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Halide Reaction Comments
Methyl SN 2 SN 1 never observed
PrimarySN 2 & E2(Primarily SN 2)
SN 2
main reaction with strong Nu-
E2 only with strong, bulky bases like
K tert-butoxide
Secondary
SN 2 & E2SN 1 & E1
SN 2 & E2 with strong bases/ good Nu-
SN 1 & E1 with weak Nu- in polar
protic solvents
TertiarySN 1 & E1E2
SN 1 & E1 with poor Nu- /weak bases
E2 with strong bases
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