1-B1 a, a,a, a'-Tetrabrom-p-xylol aus p-Xylol T2 H3C h Br2HC Start Br-Br : 2Br Propagation H CH? HBr H3C H3C CH2 CH2Br H3C CHBr2 Br2HC 1-B2 trans-4-Bromcrotonsaureethylester aus Crotonsaureethylester COMeT NBS CO2Et CCl42AiBN,△ 1-B21-B1 α,α,α´,α´-Tetrabrom-p-xylol aus p-Xylol ∆, hν H3C CH3 CHBr2 Br2HC Br2 Br Br 2Br hν Start Propagation H3C H2 C H Br H3C CH2 HBr H3C CH2 Br Br H3C CH2Br Br CHBr2 Br2HC 1-B2 trans-4-Bromcrotonsäureethylester aus Crotonsäureethylester 1-B2 CO NBS 2Et Br CO2Et CCl4 ,AiBN, ∆