Topscore, Test 1, #94 natural science

[alexamasan]

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Sadly I can't find a way to copy the problem onto a post.

But if anyone has topscore, could you help explain the answer to #94 in natural science section in test 1? It's about R/S configuration and it just seems to me that the answer should be C, but can someone explain please?

 

[mestmet31]

To do fisher projections like this..you have to put the "worst" subgroup pointing away (usually it is a Hydrogen). In this case it the methyl group on the left. You switch it with the carboxylic acid and you find out if it is R or S. However after you get R or S it is the opposite one since you made a switch.

choice A is correct because you switch the H with the methyl group. At first you get S but since you switched one of the groups it is R.

The "worst" group always has to be pointing away..I usually just put it on top

 

[Valigator00]

Sadly I can't find a way to copy the problem onto a post.

But if anyone has topscore, could you help explain the answer to #94 in natural science section in test 1? It's about R/S configuration and it just seems to me that the answer should be C, but can someone explain please?

It is not C, because the methyl group has the lowest priority. It is on the horizontal side, so you have to reverse the direction. Hope that helps.😀

 

[arginine1]

Since your lowest priority substituent is on the "horizontal axis", you have to reverse whatever configuration you assigned to this compound. In this example it is R but, after you reverse it, it becomes S.

 

[alexamasan]

Alright, thank you everyone

 

[Aug18DAT]

so the priorities are
1. F ---highest
2. NH2
3. COOH
4. CH3 ---lowest
is this correct? I got R for choice (c) cuz i thought COOH has higher prioprity than NH2..but there was no choice A&C so I just chose choice A as an answer.
Please correct me if i'm wrong. Thanks!!