Hoa huu co_phan ung 3.ppt

HOÁ HỌC HỮU CƠ
Organic Chemistry
CHƯƠNG 5 (t.t)
CÁC PHẢN ỨNG TRONG HÓA HỮU CƠ
GIỚI THIỆU CHƯƠNG
GIỚI THIỆU PHẢN ỨNG
PHÂN LỌAI PHẢN ỨNG
DẶC ĐIỂM PHẢN ỨNG
PHẢN ỨNG THẾ
PHẢN ỨNG CỘNG
PHẢN ỨNG TÁCH
PHẢN ỨNG OXI HÓA
PHẢN ỨNG THẾ ( SUBSTITUTION)
PHẢN ỨNG THẾ ÁI NHÂN (NUCLEOPHILIC)

PHẢN ỨNG THẾ ÁI ĐIỆN TỬ (ELECTROPHILIC)

PHẢN ỨNG THẾ GỐC TỰ DO (RADICAL)
PHẢN ỨNG THẾ ÁI ĐIỆN TỬ SE
GIỚI THIỆU

CƠ CHẾ VÀ ĐỘNG HỌC

CÁC YẾU TỐ ẢNH HƯỞNG
Electrophilic Aromatic Substitution
Electrophilic Aromatic Substitution
Mechanism
Arenium Ion Intermediates





Electrophilic Aromatic Substitution
Energy diagram
The first step: loss of aromaticity
The second step: regain of aromatic stabilization
Halogenation of Benzene
Halogenation of Benzene in presence of a Lewis acid







Fluorination very rapid (polyfluorination of the ring)
Iodine unreactive, alternative methods must be used
Halogenation of Benzene
Mechanism

Nitration of Benzene
Sulfonation of Benzene
Friedel-Crafts Alkylation
Friedel-Crafts Acylation
Substituent Effects on Electrophilic Substitution
Effects of Substituents on Reactivity and Orientation
Activating groups cause the aromatic ring to be more reactive than benzene
Deactivating groups cause the aromatic ring to be less reactive than benzene
Ortho-para directors direct future substitution to the ortho and para positions
Meta directors direct future substitution to the meta position
Activating Groups: Ortho-Para Directors
All activating groups are also ortho-para directors
The methyl group of toluene is an ortho-para director
Substituent Effects on Electrophilic Substitution
Alkyl groups and heteroatoms with one or more unshared electron pairs directly bonded to the aromatic ring will be ortho-para directors
Substituent Effects on Electrophilic Substitution
Deactivating Groups: Meta Directors
Strong electron-withdrawing groups such as nitro, carboxyl, and sulfonate





Substituent Effects on Electrophilic Substitution
Halo Substitutents: Deactivating Ortho-Para Directors
Substituent Effects on Electrophilic Substitution
Classification of Substitutents



Substituent Effects on Electrophilic Substitution
Electron-Releasing Groups
activate the ring toward further reaction
stabilize the transition state of the first step of substitution
lower DG‡ and faster rates of reaction

Electron-withdrawing groups
deactivate the ring toward further reaction
Electron-withdrawing groups destabilize the transition state
higher DG‡ and slower rates of reaction


Substituent Effects on Electrophilic Substitution
Substituent Effects on Electrophilic Substitution
Inductive and Resonance Effects: Theory of Orientation
Inductive effect



other electron- withdrawing groups ( atom directly attached to the ring with a partial or full positive charge)
Substituent Effects on Electrophilic Substitution
The resonance effect





Electron-donating resonance ability is summarized below
Substituent Effects on Electrophilic Substitution
Meta-directing Groups
have either a partial or full positive charge on the atom directly attached to the aromatic ring
Substituent Effects on Electrophilic Substitution
Ortho-Para Directing Groups
Many have a lone pair of electrons on the atom directly attached to the ring


Substituent Effects on Electrophilic Substitution
Activating groups having unshared electrons on the atom bonded to the ring exert primarily a resonance effect

Substituent Effects on Electrophilic Substitution
Halo groups are ortho-para directors but are also deactivating
The electron-withdrawing inductive effect: deactivates haloaromatic compounds toward electrophilic aromatic substitution
The electron-donating resonance effect: ortho-para directing influence
Substituent Effects on Electrophilic Substitution
Ortho-Para Direction and Reactivity of Alkylbenzenes




PHẢN ỨNG THẾ GỐC TỰ DO SR
GIỚI THIỆU

CƠ CHẾ VÀ ĐỘNG HỌC

CÁC YẾU TỐ ẢNH HƯỞNG
Mechanism of Radical Reactions
Initiation and Propagation
Mechanism of Radical Reactions
Chain termination
Occasionally the reactive radical intermediates are quenched by reaction pathways that do not generate new radicals
The reaction of chlorine with methane requires constant irradiation to replace radicals quenched in chain-terminating steps
Mechanism of Radical Reactions
The order of reactivity of methane substitution with halogens is:
Fluorine > chlorine > bromine > iodine
Monochlorination of alkanes proceeds to give some selectivity
Tertiary hydrogens are somewhat more reactive than secondary hydrogens which are more reactive than primary hydrogens

Tertiary, secondary and primary hydrogens


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CLO HÓA PROPAN
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CLO HÓA PROPAN
CLO HÓA PROPAN
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BROM HÓA PROPAN
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