Determinação da Configuração R-S

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Keys to the Chapter 81 where the left-hand bond goes to the stereocenter and "etc." means "continuing around the ring." Priorities are assigned in accordance with rule 2 again, because in all three groups the first atom in the "chain" attached to the asymmetric carbon is identical (carbon). We move out to the atoms attached to each of these carbons for comparison (circled): First point of difference H H C H₃ C C H₃ C C C C H₂ etc. H H C H₃ Ethyl Ring CH₂ Ring C(CH₃)₂ In each case the largest of these atoms is carbon. No difference. However, in the case of the group at the right, the second largest is also carbon, whereas the second largest for the other two groups is hydrogen. The high- est priority of these three groups is therefore the ring-contained Second and third pri- orities are determined by moving one atom further out, as shown (circled): First point of difference H C H₃ CH₂ C H CH₂ C etc. H C H₃ Ethyl Ring CH₂ Comparison here is straightforward. The CH₂ in the ethyl is connected only to a simple CH₃ group, whereas the CH₂ of the ring is attached to a group. So the latter one is higher in priority (C larger than H). Therefore we have: H d a C becoming C III C c (d in back) b CH₂CH₃ b (CH₃)₂C a Counterclockwise = S Example: Determine R-S designation for the marked carbon in CHCH(CH₃)₂ * C H CHCH₂CH₃ CI