CHEM 3331 1nd Edition Lecture 10 Outline of Last Lecture I. Multistep reactionsII. Other halogenationsIII. Hammond postulateIV. Reactive intermediatesOutline of Current Lecture I. Stereoisomers redefinedII. SymmetryIII. EnantiomersIV. Chiral centersV. NomenclatureVI. Optical activityCurrent LectureI. StereoisomersDefinition: same molecules with different orientations in substituents. For example fumeric acid and maleic acid are stereoisomers. The melting point of fumeric is 287˚C. the melting point of maleic is 138˚C and is toxic.II. SymmetryChiral= not superimposable with its mirror image. Achiral= superimposable with mirror image.A carbon with four different substituents is not superimposable with its mirror image isomer and is chiral.III. EnantiomersThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Enantiomers are mirror images that are not superimposable. They exist in pairs. IV. Chiral centersIn the example above the chiral center is the sp3 hybridized carbon. If there is no chiral center it is achiral. If there is one chiral center it is chiral. If there are two or more chiral centers it could be either. Molecules with lone pairs are chiral but unstable. If a molecule has a line of symmetryit must be achiral. V. NomenclatureMake the center your carbon atom.1) give substituents priorities by atomic mass. Higher mass= higher priority. If they tie keep going until first point of difference. If you have double or triple bonds make them into single bonds.2) rotate the molecule so the 4 priority is facing away from you.3) draw a curved line from one to two to three. If the line is clockwise, then it is r carbon configuration. If it is counterclockwise, then it is s carbon configuration.VI. Optical activity For enantiomers everything is the same (bp,mp, density, etc.) the only thing different is the plane of polarized light. Two enantiomers will rotate light in opposite directions. [α]=α(observed)/[c]*L. c=
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