Nomenclature 3 Flashcards
IUPAC Rules for assigning configuration at a tetrahedral stereocenter: #1
1: Assign priortities 1-4, with 1 being the highest, to each of the four substituents bonded to the stereocenter
IUPAC Rules for assigning configuration at a tetrahedral stereocenter: #2
orient the molecule so that the lowest priority substituent is pointed AWAY from you
IUPAC Rules for assigning configuration at a tetrahedral stereocenter: #3
Designate R or S:
R: priority 1,2,3 substituents are arranged CLOCKWISE
S: priority 1,2,3 substituents are arranged COUNTERCLOCKWISE
Cahn-Ingold-Prelog Priority Rule #1
- If the atom’s at the substituent’s points of attachment are DIFFERENT:
a) atom with higher atomic number has priority
b) atoms have the same atomic number but are isotopes, the heavier isotope has priority
Cahn-Ingold-Prelog Priority Rule #2
if atoms at point of attachment are identical, then priorities of the substituents are set one bond away, following rule 1
a) compare each set’s highest priority atom - if different, atom with highest priority corresponds to substituent with higher priority substituent
b) if highest priority atoms are identical, compare each set’s second-highest priority atom to break tie
c) if second-highest priority atoms in the two sets are identical, then compare each set’s lowest priority atom to break the tie
Cahn-Ingold-Prelog Priority Rule #3
If sets of atoms 1 bond away from the point of attachment are identical, then rule 2 is applied to sets of atoms 1 additional bond away from the point of attachment. Continue to move further away until there is a difference.
a) if substituent’s backbone is branched, then follow the chain on which the higher-priority atoms come first
b) if the 2 atoms being compared are the same and one of them is a terminal atom, then the substituent to which it belongs has the lower priority
c) if a point of difference is never encountered, then the substituents must be identical
If atoms x & y in a substituent are connected by a double bond, then we treat x as being ________ and y as being ___________.
singly bonded to two y atoms and y as being singly bonded to two x atoms
If atoms x & y in a substituent are connected by a triple bond, then we treat x as being ________ and y as being ___________.
x as being singly bonded to 3 y atoms and y as being singly bonded to 3 x atoms
If multiple stereocenters exist in a molecule:
each stereocenter receives its own (R) or (S) designation
When naming multiple stereocenters the designation appears:
before any number that identifies the location of a substituent on the corresponding stereocenter (R) or (S)
Vertical bonds in a Fischer projection point _______ you and horizontal bonds point __________ you.
away from, toward
In a Fischer projection, the proper orientation of the lowest priority group is:
a vertical bond, up or down doesn’t matter
If two molecules are related by the inversion of some, but not all tetrahedral stereocenters, they are:
diastereomers
If two molecules are related by the inversion of all tetrahedral stereocenters, they are:
enantiomers
Protocol for assigning E/Z:
determine which of the two substituents on each alkene has the higher priority
if the 2 higher priority groups are on the ZAME ZIDE: assign Z
If the two higher priority groups are on EITHER side: assign E