CHEM 2211 1st Edition Lecture 9Outline of Current LectureI. Rotation about the Double BondII. Conformation vs. ConfigurationIII. Chiral MoleculesIV. Isomer with one Asymmetric CenterV. Drawing EnantiomersCurrent Lecture Chapter 4I. Rotation around Double bondsa. Rotation can NOT occur around a double bond unless the bond is broken firstb. Leads to cis-trans isomers aka geometric isomersi. The cis-isomer has substituent on the same sideii. Trans-isomers have substituents on the opposite sidesc. Each molecule is different and has a different reactivityd. Example: Cis-Pentene vs. Trans-PenteneIsomersStereoisomersCis/Trans IsomersIsomer with Asymetric CenterConstitustional Isomerscis-Pentenetrans-PenteneII. Conformation vs. Configurationa. Conformations are different spatial arrangements for the same moleculeb. Configurations are different compounds from each other and can be separated from each other in a mixtureIII. Chiral moleculesa. Chiral molecules are nonsuperimposable, mirror images of themselves much like the left and right handsb. Achiral molecules are superimposable mirror imagesc. Chiral molecules are the result of a carbon bonded to four different substituents(aka a asymmetric center)IV. Isomers with one Asymmetric Centera. Enantiomers are molecules that cannot be superimposed on each otherb. Stereocenters are both asymmetric centers and the sp2 carbon of an alkene or the sp3 carbon of a cyclic compoundV. Drawing Enatiomersa. Perspective formula shows the bonds in the plane of the paperi. A wedge means it’s coming out of the planeii. A hatched wedge means its receding away from the planeBoth configurations of 2-bromobutaneb. Fischer projections show that the bonds intersect at the central carboni. Vertical lines are bonds that extend backwardsii. Horizontal lines are bonds that extend forwardConfigurations of 3-chlorohexaneVI. The R,S Naming System for Enantiomersa. Rank the substituents in order of highest to lowest priority. Priority is determinedby the atomic number of the atom directly bonded to that carbon. The higher the atomic number, the higher the priority.b. If the lowest priority group is bonded by a hatched wedge, then draw an arrow from the highest priority substituent to lowest priority substituent. If it turns clockwise (right) then it gets the R configuration. If it turns counterclockwise (left) then it gets the S configuration.(R)-2-bromobutane(S)-2-bromobutanec. If the lowest priority group is not bonded by a hatched wedge, then interchange group 4 with the group with the hatched wedge and do just like in step two.The CH3 was interchanged with the
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