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Unformatted text preview: c 7-4w5ithontinued rearrangement
h ydride shift ( a) 7- 4 major Zaitsev 61,
/' .... /' m ajor + (c ) � +�
m aj or mInor "y
minor (b) maj or + m inor only product from E2anti -coplanar is possi ble only from carbon wi thout CH3 by rem (d) major
ax (e) minor N y
D �� 3 ) (CH3hC -.£:::::i CI
eq C l 7- 4 7 The conformation must be considered because the leaving group must be in an axi al position. The t-butyl group is so large that it must be equatori al , locking the conformation into the chair shown. As a result, only the Cl at position i s axial, so that is the one that must leave, not the one at position 3. Two isomers are possible but it is difficult to say which would be formed in greater amount. � .�H�
. H V H' , H etc I 0
H 4 + H '- �
_ - H20 �
__ HSO4- .. .. --� - ct OSO 3H H 154 El w orks well because only one carbocation and o nly one alkene are possible. Substitution i s not a problem here. The only nuc leophiles are water, which would s i mply form starting material by a r everse of the dehydration , and bisulfate anion. Bisulfate anion is an extremely weak base and poor nucleophile; if it did attack the carbocation , the unstable product would quickly re-ionize, with no net change, bac k to the carbocation. / () +C
H H '\ H ...
' • H 20 . " � ...
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This note was uploaded on 02/27/2010 for the course CHEM 140 taught by Professor Wade during the Spring '10 term at Whitman.
- Spring '10