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828 Chapter 27
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7.
Decreasing ability to undergo cationic polymerization is in the same order as decreasing stability of the
carbocation intermediate. (Electron donation increases the stability of the carbocation.)
CH CH
2
OCH
3
CH CH
2
CH
3
CH CH
2
NO
2
>
>
donates electrons
by resonance
withdraws electrons
by resonance
CH
2
CH OCH
3
>
CH
2
CHCH
3
>
donates electrons
by resonance
withdraws electrons
by resonance
O
CH
2
CH CCH
3
CCH
3
CH
2
CH CH
2
>
A tertiary benzylic cation is more stable
than a secondary benzylic cation.
8.
Decreasing ability to undergo anionic polymerization is in the same order as decreasing stability of the
carbanion intermediate. (Electron withdrawal increases the stability of the carbanion.)
a.
CH CH
2
OCH
3
CH CH
2
CH
3
CH CH
2
NO
2
>
>
donates electrons
by resonance
withdraws electrons
by resonance
b.
CH
2
CHC N
>
CH
2
CHCl
CH
2
CHCH
3
>
withdraws electrons
by resonance
withdraws
electrons inductively
9.
Methyl methacrylate does not undergo cationic polymerization because the carbocation propagating site
would be very unstable, since the ester group is strongly electron withdrawing.
+
CH
2
CH
C O
OCH
3
propagating site
a strongly electron-withdrawing group