Chapter 3.3: Naming Chiral Centers- The R,S System Flashcards
What is which of the two possible isomers an enantiomer is?
absolute configuration
How do you assign priority to chiral atoms?
o Each atom bonded to the chiral center is assigned a priority. Priority is based on atomic number; the higher the atomic number, the higher the priority
o If priority cannot be assigned on the basis of the atoms bonded directly to the chiral center [because of a tie (i.e., the same first atom on more than one substituent)], look at the next set of atoms and continue until a priority can be assigned. Priority is assigned at the first point of difference. If two carbons have substituents of the same priority, priority is assigned to the carbon that has more of the higher priority substituents.
o Atoms participating in a double or triple bond are considered to be bonded to an equivalent number of similar “phantom” atom by single bonds; that is, atoms of the double bond are duplicated and atoms of a triple bond are triplicated. The phantom atoms are bonded to no other atoms.
Define absolute configuration
which of the two possible isomers an enantiomer is
When looking down the lowest priority bond, what is R?
1,2,3 in clockwise direction
Define R,S System
a set of rules for specifying absolute configuration about a chiral center; also called the Cahn-Ingold-Prelog System
When looking down the lowest priority bond, what is S?
1,2,3 in counterclockwise direction
When looking down the lowest priority bond, what is 1,2,3 in a counterclockwise direction?
S
When looking down the lowest priority bond, what is 1,2,3 in a clockwise direction?
R
What is a set of rules for specifying absolute configuration about a chiral center; also called the Cahn-Ingold-Prelog System?
R,S System
