O-Chem Destroyer # 186--pLEASE hELP

[Tooth09]

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Can someone please explain why C #2 is R and C3-S and C4-S... I thought C2-S, C3-R, C4-R.. Thank you...

 

[topdent1]

Look, you need to be able to assign priority to the atoms (priority is assigned my M.W) Also, vertical hydrogens retain the configuration you came up with and horizontal hydrogens force you to switch it. I'll do C-2.

First priority is Cl. Second priority is C-3. Third priority is C-1. This is going in a clockwise direction. Now check where the 4th priority or hyrdrogen is. It is vertical meaning we can leave the configuration clockwise or R.

 

[Tooth09]

Thanks... So for this type of questions the H--Always have to be in the Vertical ONLY???