Cahn-Ingold-Prelog Priority System Enantiomers have different spatial arrangements of the four groups attached to the asymmetric carbon. The two possible spatial arrangements are called configurations. Each asymmetric carbon atom is assigned a letter (R)or(S)based on its three-dimensional configuration. Cahn-Ingold-Prelog convention is the most widely accepted system for naming the configurations of chirality centers. 2013 Pearson Education,Inc. Chapter5 16
© 2013 Pearson Education, Inc. Cahn–Ingold–Prelog Priority System • Enantiomers have different spatial arrangements of the four groups attached to the asymmetric carbon. • The two possible spatial arrangements are called configurations. • Each asymmetric carbon atom is assigned a letter (R) or (S) based on its three-dimensional configuration. • Cahn–Ingold–Prelog convention is the most widely accepted system for naming the configurations of chirality centers. Chapter 5 16
(R)and (S)Configuration:Step 1 Assign Priority ·Assign a relative“priority”to each group bonded to the asymmetric carbon. Group 1 would have the highest priority, group 2 second,etc. Atoms with higher atomic numbers receive higher priorities. I>Br>CI>S>F>O>N>13C>12C>2H>1H 2013 Pearson Education,Inc. Chapter5 17
© 2013 Pearson Education, Inc. (R) and (S) Configuration: Step 1 Assign Priority • Assign a relative “priority” to each group bonded to the asymmetric carbon. Group 1 would have the highest priority, group 2 second, etc. • Atoms with higher atomic numbers receive higher priorities. I > Br > Cl > S > F > O > N > 13C > 12C > 2H > 1H Chapter 5 17
Assign Priorities CH H NH2 Atomic number:F N C H 2013 Pearson Education,Inc. Chapter5 18
© 2013 Pearson Education, Inc. Assign Priorities Atomic number: F > N > C > H Chapter 5 18
(R)and (S)Configuration: Breaking Ties In case of ties,use the next atoms along the chain of each group as tiebreakers. Examples H H CH3 CH2Br C-Br C>-C- CH3> C-CH3 >-CH2CH2CH2CH3 H CH3 2013 Pearson Education,Inc. Chapter 5 19
© 2013 Pearson Education, Inc. (R) and (S) Configuration: Breaking Ties In case of ties, use the next atoms along the chain of each group as tiebreakers. Chapter 5 19
(R)and(S)Configuration: Multiple Bonds Treat double and Rt-c becomes H triple bonds as if break and duplicate each were a bond to H a separate atom. R-C=N becomes R-C break and duplicate R一C=C一H becomes R一C CH break and duplicate C OH OH R-C=0 becomes R break and duplicate 2013 Pearson Education,Inc. Chapter5 20
© 2013 Pearson Education, Inc. (R) and (S) Configuration: Multiple Bonds Treat double and triple bonds as if each were a bond to a separate atom. Chapter 5 20