alkena-2.ppt

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8. Alkena: Pembuatan dan Reaksi Based on McMurry’s Organic Chemistry 6 th edition

Transcript of alkena-2.ppt

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8. Alkena: Pembuatan dan Reaksi

Based on McMurry’s Organic Chemistry

6th edition

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McMurry Organic Chemistry 6th edition Chapter 7 (c) 2003

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Pembuatan Alkena: Reaksi Eliminasi

Alkena biasanya dibuat dengan cara:

•Dehydration Alkohol Tersier

CH3

OHH2SO4, H2O CH3

+ H2O

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Pembuatan Alkena: Reaksi Eliminasi

•Dehydrohalogenation

Br

H

H

H

KOHH

H

+ KBr + H2O

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8.1 Preparation of Alkenes: A Preview of Elimination Reactions

Dehidrohalogenasi

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Reaksi-reaksi alkena

Alkena bereaksi dengan banyak elektrofil menghasilkan produk melalui reaksi adisi • Menghasilkan alkohol (bila mengadisi H-OH)

• Menghasilkan alkana (bila mengadisi H-H)

• Menghasilkan halohidrin (bila mengadisi HO-X)

• Menghasilkan dihalida (bila mengadisi X-X)

• Menghasilkan halida (bila mengadisi H-X)

• Menghasilkan diol (bila mengadisi HO-OH)

• Menghasilkan siklopropana (bila mengadisi :CH2)

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8.2 Adisi Halogen pada Alkena

2,3-Dibromobutane2-Butene

+ Br2CH3CH=CHCH3 CH3CH-CHCH3CH2Cl2

trans-1,2-Dibromo-cyclohexane

Cyclohexene

+ Br2

Br

Br

CH2Cl2

Br Br

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• Step 1: Pembentukan bridged bromonium ion intermediate

• Step 2: Penyerangan ion halida dari arah yang berlawanan (opposite side) dari cincin anggota tiga

Anti (coplanar) orientationof added bromine atoms

C C

Br

Br

+ C C

Br ::-

Br

:: ::

::

:

: ::C C

Br

C C

Br

Br

+-

Br

:: ::

::

:

:

:

:

:

:

Mechanism

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8.3 Pembentukan Halohidrin

Reagennya Br2 atau Cl2 )

1-Chloro-2-propanol (a chlorohydrin)

Propene

+

HO Cl

CH3CH=CH2H2 O

HClCH3CH-CH2Cl2

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Mekanisme pembentukan Bromohidrin

C C

Br

R HH H

C C

Br

R HH H

C CR H

H H -Br -

bridged bromoniumion

minor contributingstructure

Br

Br:

:

:

:

:

:

:: ::

:

C C

Br

OH

H

HR

OH

H H H

+C C

Br

R HH H

::

:

:

:

::

:Step 1

Step 2

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8.4 Adisi air pada alkena: Oksimerkurasi/Reduksi

2-Butanol

+

Acetic acid

HgOAc

OH OH

CH3COOHCH3CHCHCH3NaBH4 CH3CHCHCH3 + Hg

H

Acetic acidAn organomercury compound

Mercury(II) acetate

2-Butene++

OH

HgOAc

Hg(OAc)2CH3CH=CHCH3H2 O

CH3CHCHCH3 CH3COOH

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Addition of Hg(II) and oxygen is anti & stereoselective

(Anti addition of-OH and -HgOAc)

CyclopenteneH HgOAc

H H

OH HHg(OAc)2

H2 O

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Mechanism of Oxymercuration 1. Electrophilic addition of Hg(OAc)2 produces

mercurinium ion. 2. Water acts as a nucleophile, attacks the more

substituted carbon atom to form a C-O bond. Acetate ion removes hydrogen, forming a neutral

product, but the HgOAc is still attached. NaBH4 reduces the HgOAc, replacing it with a

hydrogen atom to form the alcohol product.

H3CHg OAc

OAc

H3CHg

OAcH3C Hg

OAc

H2O

H3C

O

H H

HgOAc

OAc OH

HgOAcH3C

NaBH4- H+

H3C

HO

H

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8.5 Adisi air pada alkena: Hidroborasi

Boran adalah asam Lewis yang mampu menerima elektron

Boran diadisi alkena menghasilkan organoboran

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Orientasi dalam hidrasi melalui Hidroborasi

Regiokimianya berlawanan dengan orientasi Markovnikov• OH terikat pada karbon dengan atom H paling banyak

H and OH add with syn stereochemistry, to the same face of the alkene (opposite of anti addition)

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Hidroborasi, Efek Elektronik memberikan Non-Markovnikov

More stable carbocation is consistent with steric preferences

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Mekanisme Hidroborasi

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8.7 Reduksi Alkena: Hidrogenasi Alkena bereaksi dengan H2dengan adanya katalis

logam transisi menghasilkan alkana

• commonly used catalysts are Pt, Pd, Ru, and Ni

Proses ini disebut reduksi katalitik (catalytic reduction) atau hidrogenasi katalitik (catalytic hydrogenation)

+ H2Pd

Cyclohexene Cyclohexane

25°C, 3 atm

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Mechanism of Hydrogenation

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8.8 Oksidasi alkena: Hidroksilasi dan Pemutusan

Hidroksilasi mengadisi OH pada kedua karbon C=C Dikatalisis oleh osmium tetroksida Stereokimia adisi adalah syn Produknya adalah 1,2-dialkohol or diol (disebut juga

glikol = glycol)

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Ozonolisis alkena

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Structure Elucidation With Ozone

Cleavage products reveal an alkene’s structure