CHEM 2211 1nd Edition Lecture 11 Outline of Last Lecture I Chapter 4 a Chirality Outline of Current Lecture I Chapter 4 a Optically active b Cyclic and meso compounds c Naming with more than one asymmetric center Current Lecture Optically active Enantiomers share many of the same properties such as boiling point and melting point and so on One of the only things that is different is the way they are arranged in space because of this the other thing that is different between them is how they react with plane polarized light The two different enantiomers will rotate light the same amount in different directions Direction is represented by these two symbols or Optically active compounds Will rotate the plane polarized light Such as enantiomers And chiral compounds Optically inactive compounds Will not rotate the plane polarized light at all These 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 Achiral compounds Racemate mixtures A racemate mixture A mixture with equal amounts of two enantiomers Dextrorotatory light rotates clockwise Levorotatory light rotates counterclockwise Do not confuse R and S with and R can be either or and so can S Although like R and S and get put in the name of a compound in the front in parenthesis Along with adding a part to naming for isomers using polarized plane light it also helps figure out enantiomer excess when there is a mixture of enantiomers This is done using the equations enantiomer excess observed specific rotation specific rotation of pure enantiomer X 100 Cyclic and meso compounds In a cyclic compound look for how many asymmetric centers you have then use this to figure out how many steroisomers you have Using 2 n n being the number of asymmetric centers Remember because the compound is cyclic the steroisomers can be cis or trans A meso compound appears when we have a compound with 2 asymmetric centers but only 3 steroisomers this is because the first steroisomer is achiral o it is because the missing steroisomer happens to be the mirror image of the first this means it has a superimposable mirror image making it achiral making the whole compound only have 3 steroisomers This is easiest to identify in perspective diagrams Naming a compound with more than one asymmetric center 1 use the same steps as the last notes on naming 2 determine the priority of the atoms around each asymmetric center 3 then draw the arrows to determine directions clockwise or counter 4 assign R or S to each asymmetric center 5 for the name instead of just putting the R or S in front of the whole name in parenthesis you have to put the letter R or S with the number carbon it applies to such as for two asymmetric centers R2 S3 name
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