Signing R and S

[YoonS]

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I am little bit confused about signing S and R on fischer projection.

Let say you have F, Br, and CHO as your constituents, which one gets

priority 1 and 2?

Also, F, NH2, and COOH

Thank you!

 

[bharat008]

I am little bit confused about signing S and R on fischer projection.

Let say you have F, Br, and CHO as your constituents, which one gets

priority 1 and 2?

Also, F, NH2, and COOH

Thank you!

For F, Br, and CHO = I would say 1st is Br, 2nd is F, and 3rd is CHO
For F, NH2, and COOH = 1st is F, 2nd is COOH, and 3rd is NH2..

 

[UCB05]

I am little bit confused about signing S and R on fischer projection.

Let say you have F, Br, and CHO as your constituents, which one gets

priority 1 and 2?

Also, F, NH2, and COOH

Thank you!

Look for Atomic Number at the first point of difference. For the first, it's -F, -Br, and -C-. Therefore Br>F>CHO

For the second, it's -F, -N-, and -C-. Therefore F>NH2>COOH

 

[bharat008]

Look for Atomic Number at the first point of difference. For the first, it's -F, -Br, and -C-. Therefore Br>F>CHO

For the second, it's -F, -N-, and -C-. Therefore F>NH2>COOH

yeah i think u r right.. NH2 has higher priority than COOH.

 

[UCB05]

For second one, i think NH2 would be last..
COOH is attached to the chiral carbon which is attached with F and NH2. Since COOH is attached to 1 double bond to O and 1 with single bond.. you pretty much have 3 OOO ... And O has a higher atomic number than NItrogen so COOH has higher priority..

Its hard to explain like this. Draw it out and it should be easier to see..

O may have a higher atomic number than N, but that is irrelevant. the O's are attached to a C, which is the first point of difference. - N-H2 has a higher priority over -C-OOH

 

[bharat008]

O may have a higher atomic number than N, but that is irrelevant. the O's are attached to a C, which is the first point of difference. - N-H2 has a higher priority over -C-OOH

yup.. i realized what i did wrong.. thanks for pointing it out..