Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Identify the indicated hydrogens in the following molecules as pro-R or pro-S :
(a) 
(b) 
Options:
Answer:
Solution:
Ans. (a) The dashed H is pro-R and the wedged H is pro-S. (b) The wedged H is pro-R and the dashed H is pro-S.
Sol. Rule: mentally replace the H under test by D (higher priority than H) and assign the configuration of the resulting stereocentre; if it is R the replaced H is pro-R, if S it is pro-S.
(a) 1-Bromo-2-chloropropane, BrCH2-CH(Cl)-CH3 : at the CH2 carbon the priorities are Br CH(Cl)CH3 D H. Replacing the dashed H by D gives the R configuration, so the dashed H is pro-R; replacing the wedged H by D gives S, so the wedged H is pro-S.
(b) Leucine, (CH3)2CH-CH2-CH(NH3+)-CO2- : at the CH2 carbon the priorities are CH(NH3+)CO2- CH(CH3)2 D H (the N-bearing carbon outranks the isopropyl carbon). Replacing the wedged H by D gives the R configuration, so the wedged H is pro-R; replacing the dashed H by D gives S, so the dashed H is pro-S.
