9 z zusammen together e entgegen opposite e z is from

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9 Z , Zusammen (together) E , Entgegen (opposite ) E , Z is from the German: E/Z System for Distinguishing Alkene Isomers Also, for more than two substituents the cis/trans system cannot be used: H CH 3 E/Z System We need to assign priorities to each substituent on each carbon using Cahn-Ingold-Prelog priority rules (more on this later) In cases where high priorities are on the “zame zide” , we assign a Z configuration ( zusammen = together in German). In cases where high priorities are on opposite sides, we assign an E configuration ( entgegen = opposite in German). low priority high priority high priority low priority high priority low priority high priority low priority
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10 E/Z System: Priority Rules Priorities are first assigned based on atomic numbers: H 3 C I H F I > C 1 2 F > H 1 2 ( E )-1-fluoro-2-iodopropene ( Z )-1-fluoro-2-iodopropene I > C 1 2 F > H 1 2 H 3 C I F H If you can’t decide using the first atoms attached, look at the next attached atoms. If there are nonequivalent paths, always follow the path with atoms of higher atomic number. The priority is determined by the attached atoms. path goes to O, not H path goes to C, not H comparison stops here (first point of difference) C H O H C H C H Z -configuration 1 2 1 2 H H 3 C CH 2 CH 2 OH CH 3 (C attached to O, H, H) (C attached to C, H, H) (O, H, H) > (C, H, H) E/Z System: Priority Rules
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11 Atoms in double bonds are replicated at either end of the double bond.
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