CHEM 2211 1st Edition Lecture 10 Outline of Last Lecture I Chapter 4 a Types of isomers Outline of Current Lecture 1 Chapter 4 a Chirality Current Lecture Chirality To be chiral Is when an object has a right handed and a left handed form The object has a non superimposable mirror image To be achiral Has a superimposable mirror image The cause of chirality is asymmetric centers An asymmetric center Also called a chiral center It is an atom bonded to four different groups Since it has to be bonded to four different groups only an sp3 carbons can be a asymmetric center An asymmetric center can also be called a stereocenter but they are slightly different A stereocenter is an atom at which that interchange of two groups produces a stereoisomer o Stereocenters therefore include both asymmetric centers and cic and trans isomers 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 Thus all asymmetric centers are stereocenters but not all stereocenters are asymmetric centers Isomers with one asymmetric center Enantiomers Molecules that are nonsuperimposable mirror images of each other All enantiomers are chiral R and S system of naming for enantiomers 1 Rank the groups bonded to the asymmetric center in order of priority a The atomic numbers of the atoms attached determine priority i Higher the number higher the priority b If there is a tie consider the atoms attached to that atom i If there was a methyl group and ethyl group the Cs tie 1 The methyl is attached to H H H 2 The ethyl group is attached to the C H H ii Therefore the ethyl group gets higher priority cause its attached to a C 2 After numbering the four groups by priority draw an arrow from the 1st to 2nd to the 3rd priority group the way these arrows point will determine R or S a If the arrows point clockwise it is an R configuration b If the arrows point counter clockwise it is an S configuration 3 These configuration symbols R or S will go in front of the name in parenthesis If you are trying to assign R or S to an atom drawn in perspective diagram form you do all the steps above but have to pay attention to priorities and which lines they are on The lowest priority atom should be on the hatched wedge o If it is not bonded by the hatched wedge you have to switched the lowest priority atom with which ever atom is bonded on the hatched wedge After the switch draw the arrows as in step two above and assign R an S based on that Note This configuration will be opposite of the configuration you would have gotten if you didn t switch the lowest priority atom to the hatched wedge o So if the configuration is S without switching the lowest priority atom than the real configuration should be R because that is what it would be with the switch So as long as you know that you don t have to physically switch the atoms Just draw the arrows assign R or S and then choose the opposite to put with the name If you are assigning R or S using a fischer projection all the same rules apply But the lowest priority atom should lay on a vertical bond o If it does not draw the arrows find the direction clockwise for R counter for S and then use the opposite R or S for the name
View Full Document
Unlocking...