CHEM 2211 1nd Edition Lecture 16 Outline of Last Lecture I Alkenes II Nomenclature for alkenes a R and S b E and Z Outline of Current Lecture I Chapter 5 alkenes Current Lecture Examples of how to name and identify E Z and R S First off lets establish rules for naming E and Z naming is used for alkenes If there is only one double bond then the E or Z goes in front of the whole name Always goes in parenthesis R and S naming is used for atoms bonded to 4 different groups The naming is determined by a priority system o The higher the atomic number the higher the priority th If 4 priority is attached to a hatched wedge just name the asymmetric center If it is attached to a solid wedge interchange it with the group on the hatched wedge and name 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 o The configuration after interchanging the groups will be the opposite of the configuration if you just left the groups This means you can leave everything as it is don t interchange name the configuration and then use the opposite configuration Examples R and S configuration Br C CH3CH2 H CH3 Br and CH2CH3 are on the same plane as the center C H is on a hatched wedge CH3 is on a solid wedge o Solid wedge is in front of the plane o Hatched is behind the plane Assign priority to the atoms Br is 1 CH2CH3 is 2 CH3 is 3 And hatched wedge H is 4 This means we can just assign a configuration no rearrangement needed We draw an arrow from 1 to 2 to 3 to 4 and see which was it goes If it is to the right clockwise it is R If it is to the left counterclockwise it is S Above I have drawn red arrows to show direction The configuration is S The arrows move to the left or counterclockwise How would the R configuration of this atom look Br C H CH2CH3 CH3 Assign priority Br is 1 CH2CH3 is 2 CH3 is 3 H is 4 o H is still on a hatch wedge s o No rearrangement needed Draw arrows from 1 to 2 2 to 3 3 to 4 I have done this above with red arrows o R configuration n o Clockwise movement E and Z naming examples E and Z is named on priority of the 4 atoms surrounding the C C double bond they are given priority levels high or low on each side This is based on their atomic number Higher the number higher the priority Br Cl 1 C C 2 H CH3 Give each side high or low priorities 1st C Br is high priority H is low priority 2nd C Cl is high priority CH3 is low priority Both the high priority atoms are on the top side of the double bond This means it is Z Z means same side o Either top or bottom What does the E atom look like Br CH3 C C H Cl Assign priorities 1st C Br is high H is low 2nd C Cl is high CH3 is low This time the 1st C high priority is above the bond The 2nd C high priority Cl is below the bond They are on opposite sides of bond there for this is the E configuration
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