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The compound 1,2-bis-(phenylethynyl)benzene (1) undergoes
Chapter 10, Problem 10.77(choose chapter or problem)
The compound 1,2-bis-(phenylethynyl)benzene (1) undergoes reactions with aqueous acid or bromine, as shown below (J. Am. Chem. Soc. 1966, 88, 4525–4526). Propose a reasonable arrow-pushing mechanism for both of these reactions. Also provide an explanation for the configuration of the exocyclic alkene (the one that is external to the ring) in the product of the bromination reaction.
Questions & Answers
QUESTION:
The compound 1,2-bis-(phenylethynyl)benzene (1) undergoes reactions with aqueous acid or bromine, as shown below (J. Am. Chem. Soc. 1966, 88, 4525–4526). Propose a reasonable arrow-pushing mechanism for both of these reactions. Also provide an explanation for the configuration of the exocyclic alkene (the one that is external to the ring) in the product of the bromination reaction.
Step 1 of 3
The compound 1,2-bis-(phenylethynyl)benzene reaction arrow-pushing mechanism with aqueous acid is shown below:
The protonation of the triple bond result in the forming of a positive charge, which gets attacked by the adjacent double bond to form the five-membered ring structure; as a result, the other double bond acquire a positive charge and get attacked by water as the nucleophile giving keto form which tautomerizes into enol form and finally on deprotonation form the desired product.