Comparison of the mirror-image forms of 2-chloro-2,3-pentadiene reveals that they are notsuperposable. 2-Chloro-2,3-pentadiene is a chiral allene.10.9Both starting materials undergo b-elimination to give a conjugated diene system. Two minor prod-ucts result, both of which have isolated double bonds.10.10The best approach is to work through this reaction mechanistically. Addition of hydrogen halidesalways proceeds by protonation of one of the terminal carbons of the diene system. Protonation ofC-1 gives an allylic cation for which the most stable resonance form is a tertiary carbocation. Pro-tonation of C-4 would give a less stable allylic carbocation for which the most stable resonance formis a secondary carbocation.Under kinetically controlled conditions the carbocation is captured at the carbon that bears the great-
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