Dolbier HW Solutions 249

Dolbier HW Solutions 249 - 243 CONJUGATION IN ALKADIENES...

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10.26 Bond formation takes place at the end of the diene system to give a bridged bicyclic ring system. 10.27 The two Diels Alder adducts formed in the reaction of 1,3-pentadiene with acrolein arise by the two alignments shown: 10.28 Compound B arises by way of a Diels Alder reaction between compound A and dimethyl acetylenedicarboxylate. Compound A must therefore have a conjugated diene system. 10.29 The reaction is a nucleophilic substitution in which the nucleophile (C 6 H 5 S 2 ) becomes attached to the carbon that bore the chloride leaving group. Allylic rearrangement is not observed; therefore, it is reasonable to conclude that an allylic carbocation is not involved. The mechanism is S N 2. 10.30 ( a ) Solvolysis of in ethanol proceeds by an S N 1 mechanism and involves a carbocation intermediate. This carbocation has some of the character of a tertiary carbocation. It is more stable and is therefore formed faster than allyl cation,
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