CHEM 2211 1st Edition Lecture 11 Outline of Last LectureI. Isomers are Optically ActiveII. Measuring RotationIII. Enantiomeric ExcessIV. Compounds with more than One Asymmetric CenterOutline of Current LectureI. Stereoisomers of cyclic compoundsII. Meso Compounds are optically inactiveIII. How to Name Isomers with more than one Asymmetric CenterLecture NotesI. Stereoisomers of Cyclic CompoundsA. Some cyclic molecule like 1-bromo-2-methylcyclopentane have two asymmetric centers and four stereo isomersCis-isomer of 1-bromo-2-methylcyclopentaneTrans-isomer of 1-bromo-2-methylcyclopentaneB. However, other cyclic molecules like 1-bromo-3-methylcyclobutane do not have any asymmetric centers.i. Two groups are identical because substituents are equidistance from eachotherCis-1-bromo-3-methylcyclobutaneTrans-1-bromo-3-methylcyclobutaneC. Another example is 1-bromo-4-methylcyclohexane. The molecule on the left is the cis-isomer and the molecule on the right is the trans-isomer.II. Meso Compounds are optically inactiveA. Some asymmetric compounds, like 2,3-dibromobutane, only have three stereoisomersStaggered Conformer of 2, 3-dibromobutaneEclipsed Conformer of 2, 3-dibromobutaneB. Meso compounds have asymmetric centers, but are achiral because they are superimposable on their mirror imagesMeso compoundEnantiomersi. They have a plane of symmetry that runs through the middle so that one side is the mirror image of the otherPlane of symmetry for 2, 3-dibromobutaneC. For cyclic molecules, the cis isomer will be the meso compound and the trans isomer willbe the pair of enantiomersMeso CompoundEnantiomersi. Hexane has a plane of symmetry only in the boat conformationChair Conformer of HexaneBoat Conformer of HexaneIII. How to Name Isomers with more than one Asymmetric Center3-bromo-2-butanolA. Determine the priority of the constituents attached to C2 and assign it as either an R or an S. Carbon has an S configurationB. Repeat the first step with C3.Carbon is an R configurationC. The final compound is named (2S, 3R)-3-bromo-2-butanol(2S,
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