Chap 12 Conjugated unsaturated systems 12. 1 Introduction Systems that have a p orbital on an atom adjacent to a double bond---molecules with delocalized pi bonds-are called conjugated unsaturated systems 122 Allylic substitution and the allyl radical(烯丙基取代和 烯丙基自由基) CCl Low temp H2C=CHCH3 X H2C—cHcH3 (addition reaction) high temp XX H2C=CHCH3 2 H,C--CHCH2X HX (substitution reactionChap 12 Conjugated unsaturated systems 12.1 Introduction Systems that have a p orbital on an atom adjacent to a double bond---molecules with delocalized pi￾bonds– are called conjugated unsaturated systems. 12.2 Allylic substitution and the allyl radical (烯丙基取代和 烯丙基自由基） H2C CHCH3 + X2 CCl 4 (addition reaction) H2C CHCH3 X X Low temp H2C CHCH3 + X2 (substitution reaction) H2C CHCH2X + HX high temp