Die Solvolyse von α‐Bromstyrolen Substitution am ungesättigten trigonalen Kohlenstoffatom

In ‘80%’ ethanol the or‐bromostyrenes 5a ‐ 5d undergo unimolecular solvolysis to the corresponding acetophenones. In addition to acetophenone, α‐bromostyrene itself yields a minor amount of phenylacetylene. The p ‐amino, p ‐methoxy and p‐ acetamido derivatives 5b‐5c react 10 8 , 10 4 and 10 3 times as fast, respectively, as the unsubstituted compound 5a , the rates being insensitive to 1‐5 equivalents of triethyl‐ amine. Furthermore, 5a and 5c show electrophilic catalysis by silver ion. A two‐step ionisation mechanism involving a digonal carbonium ion ( p ‐R‐C 6 H 4 C=CH 2 ) + is thus indicated.