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Solutions for Reactions of Alcohols
20 continued
HClOH
ClZnCl2
HBr
Br
PBr3
Br
P
II2
SOCl2
Cl
(b) The key is that the intermediate carbocation is allylic, very stable, and relatively long-lived. It can 
therefore escape the ion pair and become a "free" carbocation. The nucleophilic chloride can attack any 
carbon with positive charge, not just the one closest. Since two carbons have partial positive charge, two 
products result.
no reaction unless heated, 
then
(a)
21 OH
I2
PBr3
HCl
HBr
P
ZnCl2
SOCl2
I
Cl
Cl
Br
Br
(poor reaction on 3°)
(poor reaction on 3°)
(poor reaction on 3°)
(b)
OH HCl
HBr
I2
PBr3
P
ZnCl2
SOCl2
I
Br
Cl
Br
Br
Cl
(c)
1°, neopentyl
no reaction unless heated, then
SN1—rearrangement
SN1—rearrangementSN2—minor
(hindered)
+
On 3° alcohols, 
these reagents 
often give more 
elimination than 
substitution.
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