datqvault- organic test 3 question 10

[jhc83]

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Can someone please tell me why the second one (the one with the ethyl group) is S and not R? (see attachment for picture)

I thought the first priority would be the OH group and then the ethyl...last being the methane...which would make a clockwise circle = R....

 

[Saiph]

C -CH-OH is Priority yes.
C -CH2-CH3 this is 3rd in priority because the first carbon is attached to two H's.
C -CH-(CH2)-CH3 this is 2nd in priority because the first carbon is attached to two carbon groups, a methyl and the other carbon in a ring.

It will be S. Good luck studying!