elektrofilik alifatik

7/25/2019 ELEKTROFILIK ALIFATIK

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Kelompok 1

Amrina Rosada

Ayu LestariSepti Andriani


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SubstitusiElektroflik Aliatik


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Tujuan Presentasi

1. Menjelaskan elektroflisitas/keelektroflan

2. Menuliskan mekanisme reaksi substitusi elektroflikunimolekuler, SE1

3. Menuliskan mekanisme reaksi substitusi elektroflik

bimolekuler, SE2

4. Menjelaskan Diaram eneri untuk reaksi substitusielektroflik bimole!ular

". Menjelaskan mekanisme reaksi SE1

#. Membe$akan peruba%an stereokimia substrat pa$areaksi SE1$an SE2

&. Menjelaskan Diaram Eneri untuk reaksi Se1sen'a(a ali)atik


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Defne o) Ele!t%rofl

Elektroflitas merupakan sesuatu'an tertarik pa$a elektron, Dankarena tertarik ole% $aera% neati),

elektrofl %arus merupakan sesuatu'an memeba(a muatan positi)penu% atau memiliki se$ikit muatan

positi) $isuatu $aera% pa$an'a.


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Ele!trop%ili! substitution rea!tionme!%anism

Differences in the mechanism of electrophilic substitutionreactions with nucleophilic substitution reaction mechanism,

lies on the species and the attackers leaving group. In the

electrophilic substitution reaction, an attacker species and

goings group is an electrophile (acid according to the concept ofLewis). Basically the changes that occur in electrophilic

substitution reaction is an electrophile (according to the concept

of Lewis acid) to form a new bond with carbon atoms of the

substrate and one of the substituents on the carbon off without a

pair electrons. lectrophile can be either positive ion, or thepositive end of a dipole

* + - + * + - +

Substrat elektrofl %asil substitusi uus

peri


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lectrophilic substitution reaction mechanism

!liphatic "ompounds

#he ability to release protons will determine the

reactivity of aliphatic compounds in electrophilic

substitution. #herefore leaving group most often found

in electrophilic substitution of aliphatic compoundsare protons.

#he mechanism is divided into two, namely$

%. #he mechanism of electrophilic substitution

unimolekuler (&%)

'. Bimolecular electrophilic substitution mechanism

(&' and &I)


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%. #he mechanism of electrophilic substitution unimolekuler (&%)

lectrophilic substitution reaction mechanism unimolekuler (&%)

consists of two stages, namely the ioniation stage which takes

place slowly and is a decisive stage of the reaction rate, and the

ointing stage carbanions with electrophiles rapid.

lambatTa%ap 1. *0 *0 - -

!epat

Ta%ap 2. *0 - -* + Elektrofl

#he reaction rate which follows &% mechanism is not affected by

the concentration of electrophile as a determinant of the rate of the

reaction stage is the stage of ioniation (carbanion formation).


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#he reaction products that follow &% mechanism can produce

products by maintaining its original configuration (retention), or

racemiation or inversion configuration (inversion) in part,

depend on factors carbanion stability, concentrationelectrophiles, strength electrophiles and carbanions

configuration.

#he reaction will produce racemisation if$%) .*arbanion stabilied by delocaliation and low concentration

or strength electrophile electrophile low,

') .*arbanion flat structure and a negative charge delocalied

carbanions so electrophile can attack from both sides,+). "arbanion structure but form a tetrahedral anion euilibrium

enantiomeric mi-ture at a rate faster than the rate of formation

of the product.


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"arbanions which tetrahedral structure is described as

follows$

&% reaction which takes place by maintaining the original

configuration (retention) can occur in two ways$

%). lat and solvated carbanion structure is not symmetrical by

electrophiles on the same side of the position leaving group,'). "arbanion structure tetrahedral and carbanions electrophile

bound before changing to enantiomernya structure.

C

c

b

aa

b

c

C


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-amples &% reaction which takes place

by maintaining the original configuration is$

C

n-C6H5H3C

C6H5SO2

D + OCH3- (CH3)2SO

25 oC

C6H5SO2

H3C

n-C6H5

C

C6H5SO2

H3Cn-C6H5

C HHOCH3

enantiomer murni

retensi 90 %


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&% reactions that produce products with configuration

reversal (inversion) occurs on systems with flat and solvated

carbanion structure is not symmetrical as an intermediate

(intermediate). #his anion solvated on the same side of theposition leaving group by a molecule that is formed from the

group to go and electrophile attack from the opposite side.

-ample $ #he reaction between the anion of +/phenyl/',+/

dimethyl/'/pentanol with ethylene glycol.

karbanion tersolasi tak simetris sebaai at antara

HOCH2

C2H5H3C

210 oCCH3C

C6H5

H3C

C2H5

C

CH3

O-

+ HOCH2CH2OH

(eletro!il)

CH2O-H C C CH3

O

C2H5 CH3

-

H - "C + C # O

CH3

CH3CH3

C6H5

C2H5

+ CH2OHCH2O-


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'. Bimolecular electrophilic substitution mechanism (&' and &I)

Bimolecular reaction mechanisms of electrophilic

substitution in aliphatic compounds occurs through breaking

the bond between the leaving group with a substrate and

forming a new bond between the electrophile with the

substrate takes place at the same time. #herefore, the reactionrate is influenced by the concentration of electrophile and the

substrate. !n e-ample is the reaction of alkyl mercury iodide

changes into alkyl iodide to triiodide ion electrophile with the

following mechanism$

CH3CH2CH2 H$ % + %% %- H2O

&iosanCH3CH2CH2 % + H$%2 + %

-


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!t &' mechanism, there are two possible

directions of electrophilic attack on substrates,

ie from the front, called &' (front) and fromthe back, called &' (rear) can be described as

follows$

C '

c

b

a + a

b

c

C + '+ (S2 &e*an)

a

b

c

'C

a

b

c

C+ + '+ (S2 belaan$)


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If the reaction occurs in a chiral substrate is

formed by the reaction product retains its

original configuration (retention) in &'mechanism (front), and a reversal of

configuration (inversion) in &' mechanism

(rear). If electrophiles attack the substrate from

the front there is a possibility that a third

mechanism, which is one part of the escape

group electrophile help go and at the same

time to form a new bond with the substrate.

+ '-,(C

c

b

a

C '

c

b

a

( ,


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0ost reactions are bimolecular electrophilic substitution

(second order) to produce products with maintaining the

original configurations. #his means that in general, the reaction

proceeds by a mechanism wherein the substrate electrophileattack from the front, &' (front) or &I.

#his fact is contrary to the &1' mechanism. In the &1'

mechanism, the nucleophile attacks the carbon atom with the

group away, while the attacking electrophile &' mechanism ofelectron binding carbon atom and leaving group. #herefore, the

reaction proceeds more rapidly if electrophiles attack the

substrate from the same side of the position leaving group than

otherwise due to steric hindrance.

CC

H

CH3 H$ r + r r

C2H5

CH3

H

r + H$r2

C2H5


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nergy diagram for bimolecular electrophilic

substitution reaction


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lectrophilic substitution is accompanied

by displacement of the double bond2earrangement will occur in the reaction product, if the

electrophilic substitution reactions occur on allylic substrate.

#he mechanism of formation of products that undergorearrangement can occur in two ways$

%. #he reaction takes place as the mechanism &%, where the

group went off first establish if a resonance stabilied

carbanion, followed by the electrophile attacks


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'. electrophile 3 4 strike first substrate to form

carbocations and followed with the release of

5 4 as a leaving group.

In general, the electrophilic allylic

rearrangement involving hydrogen as the

leaving group, although it can also occur in the

organometallic compound with a metal ion asa leaving group

C # C C ' -'+

C # C C C C # C(+

( C C # C

*ro&u

*ro&u

(

C # CCCC C'C# CC

(+

(

'

++ '+


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#he relationship between the structure of the

substrate and its reactivity in electrophilic

substitution of aliphatic compounds

In the reaction mechanism &%, has a decisive stage of the

reaction rate similar to the release of a proton from an acid.

#herefore, the electron booster groups will reduce the rate of

reaction and vice versa electron/withdrawing groups will

increase the rate of reaction. In the reaction mechanism &'

(behind) the reactivity of the substrate as well as the &1'

mechanism, ie the greater the alkyl group, the greater the

obstruction steriknya so that the reaction rate will be smaller.

&o the order of reactivity is$ 0e6 t6 7r6 i/7r6 neopentyl.

In the reaction mechanism &' (front) reaction rate depends

on the type of reaction


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nergy diagram for the reaction of aliphatic

compounds &%

&uch as analogue &n' reaction with &', so is the case

with the reaction between the &1% reaction &%. In the

mechanism both are e-periencing the formation of an

intermediate. 8here in &% formed carbanion, while in &1%

formed carbocation, but for the energy diagram, the two havein common.

)

.

S

/

0 +

1 2

# r a n s i s i


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elektrofilik alifatik

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