[The Guy]

I have found the following question on the Chemistry GRE test guide.
My answer to this was (B) which 2R, 3S; however, the answer key show that the right answer is: (D) 2S, 3S

I have reviewed my answer several time. I just don't buy it, I am sure the right answer is B and find no reason why it would be D



The way I have ranked the priority on the left side chiral carbon is: C-OH is number 2, and C=O is number 3, and OH is 1, and H is the fourth. Because C=O is attached to and O and H (less priority than C), but C-OH attached to OH and another CH2.

Any idea if I am right or they are right?

[Vidya]

If you check in HC=O group ...it is taken as C bonded with two O and one H ..C -O,O,H
where as in CH2OH group on the right ...carbon is bonded to one carbon ,one H  and one O ...C-O,C,H
According to CIP rules who will get higher priority ?
                                                                       
Compare O with C ?
                                 

[The Guy]

If you check in HC=O group ...it is taken as C bonded with two O and one H ..C -O,O,H
where as in CH2OH group on the right ...carbon is bonded to one carbon ,one H  and one O ...C-O,C,H
According to CIP rules who will get higher priority ?
                                                                       
Compare O with C ?
                                 

Thank you for your help, I thought the O in C=O count one time. Didn't know that we count each bond.

Now it make sense.

Thanks