Bruice - Chimica Organica

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Chapter 6 231
Copyright © 2017 Pearson Education, Inc.
81. Five- and six-membered rings are more stable than smaller or larger rings.
a. Either a six-membered ring or a five-membered ring can be formed. However, because the more substituted
three-membered ring carbon has the larger partial positive charge (it is secondary, and the less substituted
one is primary), the three-membered ring breaks in the direction that forms the five-membered ring.
HOCH2CH 2CH 2CH CH 2
Br
+
..
..
..
..
Br
HOCH2CH 2CH2CH CH 2
Br
+
CH 2Br
+
O
H major product
+
O
H
O
H
CH2Br
+ +
O
H
Br
minor product
+ +
b. A six-membered ring will form in preference to a less stable seven-membered ring. (In addition,
formation of the six-membered ring involves the preferred attack on the more substituted ring carbon.)
HOCH2CH 2CH2CH2CH CH 2
Br
+
+ ..
..
O
H
CH2 Br O
H
CH 2Br
+ +
82. a. CH2CH 2CH3
C
H
Cl
CH 2CH2CH3
C
CH3 H
Cl
+
CH3
Cl
CH2CH2CH3
H
or
+
+ CH3CH2CHCH2CH3
Cl
CH3
H
CH2 CH2CH3
Cl CH3CH2CHCH2CH3
Cl
S R
S R
+
CH3
b. CH2CH 2CH3
C
H
Cl
CH 2CH2CH3
C
CH3 H
Cl
+
CH3
Cl
CH2CH2CH3
H
or
+
+ CH3CH2CHCH2CH3
Cl
CH3
H
CH2 CH2CH3
Cl + CH 3CH2 CHCH2CH3
Cl
S R
S R
CH3
c.
CH2CH3
OH