MIND MAP CHAPTER 7 HALOALKANE

MIND MAP
HALOALKANE

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PREPARATION AND CHEMICAL PROPERTIES OF HALOALKANE

CH3CH=CH2

CH3CHCH3 CH3COONa NaOH, CH3CH2OH CH3CHCH3
OCOCH3  NaOH (aq) OH

CH3CHCH3  CH3CHCH3
OCH3 OH
CH3ONa CH3CHCH3 H2O
CH3CHCH3  Br 
OCH3
CH3OH Mg excess NH3 CH3CHCH3
 KCN, alcohol dry ether  NH2

reflux

CH3CHCH3 CH3CHCH3
CN MgBr

*Grignard reagent

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RX
Halolakane
(alkyl halide)

Mg dry ether

RMgX
Grignard Reagent
(alkyl magnesium halide)

Step (i)
react with

H2O, H+ CO2
(carbon dioxide)

(methanal) (aldehyde) (ketone)

Step (ii) H2O, H+ H2O, H+ H2O, H+ H2O, H+
followed by 2o alcohol
hydrolysis

Alkane 1o alcohol 3o alcohol Carboxylic acid

RH + Mg(OH)X

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SUMMARY MECHANISM SN1 & SN2 MECHANISM

Type of SN1 SN2
Mechanism Unimolecular Nucleophilic Substitution Bimolecular Nucleophilic Substitution

General R R RCH2X +- RCH2Nu +-
Reaction
+- +- Nu X

R C X Nu R C Nu X

R R

Two steps mechanism One step mechanism

Step 1 : Formation of carbocation RR

- HCX slow δ- δ+C δ-
Nu X
R R Nu:
RC X R C + + X-
slow H HH

Mechanism RR Transition State
Steps
Step 2 : Nucleophilic attack

fast

R R
fast
R C+ - R +-
R C Nu Nu C
+ Nu X
R H
R H

Order of First order Second order
reaction Rate = k [RX] Rate = [RX] [Nu-]
Rate Law methyl halide <<< 1o < 2o < 3o
Relative 3o <<< 2o < 1o < methyl halide
Reactivity of
Haloalkanes Stability of carbocation Steric effect
Factors Weak nucleophile Strong nucleophile
influence Carbocation Transition State
Strength of
Nucleophile
Reaction
Intermediate

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UNIMOLECULAR NUCLEOPHILIC SUBSTITUTION BIMOLECULAR NUCLEOPHILIC SUBSTITUTION
@ SN1 MECHANISM @ SN2 MECHANISM

CH3 CH3 - + CH3 Cl slow CH3
CH3 C Br + H2O CH3 C OH + HBr δ- δ+ δ-
HO HC HO C Cl
CH3 CH3 H
HH
3o haloalkane
Transition State
Formation of carbocation

Step CH3 slow CH3 fast
1
CH3 C Br CH3 C+ + -

Br

CH3 CH3 CH3 + -
C
HO H Cl

Nucleophilic attack

H

Step CH3 fast CH3 H
2 CH3 C+ + H2O C +O H
CH3

CH3 CH3

Loss of proton, H+

CH3+ H CH3 +
+ H2O CH3 C OH +
CH3 C O H H3O
CH3
CH3

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UNIMOLECULAR NUCLEOPHILIC SUBSTITUTION @ SN1 MECHANISM

REARRANGEMENT: 1,2-HYDRIDE SHIFT

CH3 CH3 CH3
CH3 C CH3 + CH3CHCH2OCH2CH3 + HBr
CH3CHCH2Br + CH3CH2OH
OCH2CH3 minor product
o

1 haloalkane

major product

Step 1 : Formation of carbocation Step 2 : Nucleophilic attack & Loss of proton, H+ (Major product)

CH3 CH3 Br slow CH3 CH3 + - CH3 fast CH3
C CH2 C CH2 + CH3 C+ CH3 + CH3CH2OH CH3 C CH3
H Br
3o carbocation H O+ CH2CH3
H

o

1 carbocation

Rearrangement : 1,2-hydride shift CH3 CH3
CH3 C CH3
CH3+ CH3 CH3 C + - +

CH3 Br HBr

CH3 C CH2 1,2-hydride shift CH3 C CH3 H O+ CH2CH3 OCH2CH3
+
major product

H o Step 2 : Nucleophilic attack & Loss of proton, H+ (Minor product)

o 3 carbocation

1 carbocation

CH3 + + fast CH3 +
CH3 CH CH2OCH2CH3
CH3 C CH2 CH3CH2OH
H
H
CH3
CH3 + CH3 CH CH2OCH2CH3 + HBr
CH3 CH CH2OCH2CH3 + Br-
minor product
H

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UNIMOLECULAR NUCLEOPHILIC SUBSTITUTION @ SN1 MECHANISM

REARRANGEMENT: 1,2-METHYL SHIFT

CH3 CH3 CH3
++
+ CH3 C CH2CH3 CH3 C CH2OH NaBr

CH3 C CH2Br NaOH (aq) OH CH3
CH3
major product minor product
10 haloalkane
Step 2 : Nucleophilic attack & Loss of proton, H+ (Major product)
Step 1 : Formation of carbocation

CH3 CH3 Br slow CH3 CH3 + + Br- CH3 CH3
CH3 C CH2 C CH2 fast
CH3 CH3 CH3 C+ CH2CH3 + H2O
CH3 C CH2CH3
H O+ H

1o carbocation 3o carbocation

Rearrangement : 1,2-methyl shift CH3 CH3

CH3 C CH2CH3 + H2O CH3 C CH2CH3 ++

H3O

CH3 + CH3 H O+ H OH
C CH2 CH3 C+ CH2CH3
1,2-methyl shift major product

CH3 Step 2 : Nucleophilic attack & Loss of proton, H+ (Minor product)
1o carbocation
3o carbocation

CH3 + + fast CH3 +

CH3 C CH2 H2O CH3 C CH2O H

CH3 CH3 H

1o carbocation

CH3 + CH3

+ CH3 C ++

CH3 C CH2O H H2O CH2OH H3O

CH3 H CH3

minor product

Prepared by: NFAG, KMPh

Prepared by: NFAG, KMPh