Question

please explain, tell me, and show me how and why the answer is D?

9. What are the Cahn-Ingold-Prelog configurations at C(2) and C(5) in Penicillin G? SCHE a) C(2) is R and C(5) is R c) C(2) is S and C(5) is LYCH N -2 CH3 1 2H b) C(2) is R and C(5) is S d) C(2) is S and C(5) is R COH Penicillin G O

Answer 1

Ans. (d)

ои и NA uw'll CM Ho Atc-5: At c-2: SU om ons - N OC-oh 0com Lowest priority group (H) is away from the observer (below the plane) So configuration Heralns But Lowest priority gp (4) is towards the observer (Above the plane) so inverse the configneration. TR]

At C-2 : first of all see the directly attached atoms to the chiral Carbon . H has lowest priority (4) and now out of 2C and one N , N Will be given priority I.e (1) , then look at the next atom of these two Carbons. As one have C=O and other has S , as S is more prior to O , so Carbon having Sulfur is given (2) priority and the other carbon (3) . Then give the name S or R according to the rule.

At C-5: S is given (1), N (2) and C is given (3) priority.