Exercício de Química Sintética e Organica Mista (109)

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(d ) Dehydrobromination of 2-bromo-2-methylpentane can involve one of the hydrogens of either
a methyl group (C-1) or a methylene group (C-3).
Neither alkene is capable of existing in stereoisomeric forms, and so these two are the only
products of E2 elimination.
(e) 2-Bromo-3-methylpentane can undergo dehydrohalogenation by loss of a proton from either
C-1 or C-3. Loss of a proton from C-1 gives 3-methyl-1-pentene.
Loss of a proton from C-3 gives a mixture of (E)- and (Z)-3-methyl-2-pentene.
( f ) Three alkenes are possible from 3-bromo-2-methylpentane. Loss of the C-2 proton gives 
2-methyl-2-pentene.
Abstraction of a proton from C-4 can yield either (E)- or (Z)-4-methyl-2-pentene.
(g) Proton abstraction from the C-3 methyl group of 3-bromo-3-methylpentane yields 2-ethyl-
1-butene.
E2
2-Ethyl-1-butene3-Bromo-3-methylpentane
CH3CH2CCH2CH3
Br
CH2
H
C
CH3CH2 CH2CH3
CH2
Base:
E2
3-Bromo-2-methylpentane (E)-4-Methyl-2-pentene
:Base
(CH3)2CHCH
Br
H
CHCH3 �C C
H
(CH3)2CH
CH3
H
(Z )-4-Methyl-2-pentene
C C
H
(CH3)2CH CH3
H
2-Methyl-2-pentene
E2
3-Bromo-2-methylpentane
Base:
CH3 C
BrCH3
H
CHCH2CH3 C CHCH2CH3 
CH3
CH3
(E)-3-Methyl-2-pentene
C C
H3C
H
CH3
CH2CH3
(Z)-3-Methyl-2-pentene
C C
H3C
H
CH2CH3
CH3
�
base
E2
2-Bromo-3-methylpentane
Br
CH3CHCHCH2CH3
CH3
3-Methyl-1-pentene
base
E2
2-Bromo-3-methylpentane
CH2 CHCHCH2CH3 
CH3
Base:
H
CH2 CHCHCH2CH3
Br
CH3
2-Bromo-2-methylpentane 2-Methyl-1-pentene 2-Methyl-2-pentene
CH2
CH3
CH2CH2CH3
C
base
E2
Br
CH3
CH3CCH2CH2CH3 � (CH3)2C CHCH2CH3
104 STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTIONS