(R),(S)Nomenclature Different molecules (enantiomers)must have different names. Usually only one enantiomer will be biologically active. Configuration around the C-OH chiral carbon is specified C…H NH2 with (R)and (S). natural alanine > Chapter 5 6
Chapter 5 6 (R), (S) Nomenclature • Different molecules (enantiomers) must have different names. • Usually only one enantiomer will be biologically active. • Configuration around the chiral carbon is specified with (R) and (S). C C O OH H3C NH2 H natural alanine =>
Cahn-Ingold-Prelog Rules Assign a priority number to each group attached to the chiral carbon. Atom with highest atomic number assigned the highest priority #1. In case of ties,look at the next atoms along the chain. Double and triple bonds are treated like bonds to duplicate atoms. => Chapter 5
Chapter 5 7 Cahn-Ingold-Prelog Rules • Assign a priority number to each group attached to the chiral carbon. • Atom with highest atomic number assigned the highest priority #1. • In case of ties, look at the next atoms along the chain. • Double and triple bonds are treated like bonds to duplicate atoms. =>
Assign Priorities 0、20H C 3C..H4 H3C NH2 natural alanine H expands to H 4 H *C CH(CH3)2 CH(CH3)2 CH2OH H CH2OH 2 c-0 Chapter 5 8
Chapter 5 8 Assign Priorities C C O OH H3C NH2 H natural alanine 1 2 3 4 Cl Cl H H * 1 2 3 4 1 2 3 4 => C C O H C H CH2 CH2OH CH(CH3) 2 * C C C CH2OH CH(CH3 ) 2 H O O C C H CH2 C * expands to
Assign(R)or(S) Working in 3D,rotate molecule so that 。 lowest priority group is in back. Draw an arrow from highest to lowest priority group. Clockwise =(R),Counterclockwise =(S) rotate (S)enantiomer Chapter 5 9
Chapter 5 9 Assign (R) or (S) • Working in 3D, rotate molecule so that lowest priority group is in back. • Draw an arrow from highest to lowest priority group. • Clockwise = (R), Counterclockwise = (S) =>
Properties of Enantiomers Same boiling point,melting point,density Same refractive index Different direction of rotation in polarimeter Different interaction with other chiral molecules Enzymes Taste buds,scent => Chapter 5 10
Chapter 5 10 Properties of Enantiomers • Same boiling point, melting point, density • Same refractive index • Different direction of rotation in polarimeter • Different interaction with other chiral molecules – Enzymes – Taste buds, scent =>