Step 1
C O
CH 3
CH 3
H 3 CCH O H
H
H O +
H
H O
H
H
+
CH 3
CH 3
+ H 3 C +
Protonated alcohol
or alkyloxonium ion
1) In step 2, the leaving group is a molecule of water.
2) The carbon-oxygen bond breaks heterolytically.
3) It is a highly endergonic step and therefore is the slowest step.
Step 2
C O H
H
+ OH
H
CH 3
CH 3
H 3 C H
3 CCH 3
C
CH 3
+ +
Acarbocation
Step 3
H 3 CCH 3
C
H 2 C
OH
H
O H
H
+ + +
H
H 3 CCH 3
C
CH 2
2-Methylpropene
+ H
7.7B CARBOCATION STABILITY AND THE TRANSITION STATE
- The order of stability of carbocations is 3° > 2° > 1° > methyl:
RR
C
R
+
R H
C
R
+
R H
C
H
+
HHC
H
>>> +
3 o >> 2 o > 1 o Methyl
