Chem 261 1st Edition Lecture 16Outline of Last Lecture:I. Electrophiles and Nucleophiles as Functional GroupsII. Using Arrow FormalismIII. Polar Addition of H-Br to EthyleneIV. Degrees of UnsaturationV. Naming AlkenesOutline of Current Lecture:I. Alkene Naming ReviewII. Cis-Trans Isomers of AlkenesIII. E, Z Designation in AlkenesIV. Alkene Stability and SubstitutionAlkene Naming Review:-Chain in numbered by the largest continuous hydrocarbon sequence, but with a few exceptions…-the chain must include double bond-in cyclic alkenes, C is in the double bond**if you have substituents on the alkene, it is always numbered as carbon 1-Number of double bonds:2 = diene3= triene4= tetraeneCis-Trans Isomers of Alkenes:**must look across the double bond-Cis = bigger substituents on the toptrans = bigger substituents on opposite sides (top and bottom AND left and right)geminal: bigger substituents on same side (left or right), but one is on the top and one is on the bottom**rotation is prevented about the pi bondE,Z Designation in Alkenes:-Naming priority-cis, transdisubstituted, but multisubstituted is E, Z designationE= higher priority substituents on different sidesZ = higher priority substituents on the same side**substituents do not have to be on the same side**need different priorities on both carbons to use E/Z designationAlkene Stability and Substitution:-cis isomers = LESS stable than trans(cis = steric repulsion between substituents on the same side)-Experimental stability, evaluate heat given off when C=C is converted to C-C-In a progression of reaction graph, the cis graph will be higher (have more energy from a less stable reaction) than the trans graph. They will have different transition states but will have the same
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