Absolute Configuration

[ConfusedOne]

Advertisement - Members don't see this ad

This is a question from topscore. What would the absolute configuration of this be? R or S? Thanks

....Br
.....|
F--C--CHO
.....|
.....H

please ignore periods

 

[keibee82]

This is a question from topscore. What would the absolute configuration of this be? R or S? Thanks

....Br
.....|
F--C--CHO
.....|
.....H

please ignore periods

S

 

[ConfusedOne]

S

thanks for the quick reply 🙂

 

[slayerdeus]

ya go with S

Priority ranking:
1. Br
2. F
3. CHO
4. H

 

[ConfusedOne]

yeah thanks. My mind must be jello from all this studying. For some reason I thought F gets the priority

 

[Envision]

yeah thanks. My mind must be jello from all this studying. For some reason I thought F gets the priority

Probably bc F is the most electronegative. however, for R/S config. highest priority is given the atom with the highest atomic number.

 

[allstardentist]

hey how do u guys know if the hydrogen is pointing out of the screen or into the screen based on what he has shown? just assumed that hydrogen is pointing into the screen?

 

[dat_student]

hey how do u guys know if the hydrogen is pointing out of the screen or into the screen based on what he has shown? just assumed that hydrogen is pointing into the screen?

Don't worry about that.

1st put the lowest priority at the top.
....Br
.....|
F--C--CHO
.....|
.....H

....H
.....|
F--C--Br
.....|
.....CHO

Br (1)-->F(2)-->CHO(3) is counter clockwise. So it's S

P.S. There is a faster way.

 

[allstardentist]

oh wait, that is in fischer projection? and whats the faster way?

 

[allstardentist]

also i dont understand how u got from the first structure to the second one. can u explain how u got that? thanks.

 

[dat_student]

also i dont understand how u got from the first structure to the second one. can u explain how u got that? thanks.

keep one stationary and rotate the other three clockwise OR counter clockwise.

oh wait, that is in fischer projection? and whats the faster way?

it's been a while. you have to double check me.

faster way:

if lowest priority is at top or bottom. Look at the other three if clockwise R if counter S

if lowest p. right or left clockwise is S, counter c. is R

(faster because you don't have to put the lowest priority group at the top)

Like I said, it's been a while. you'll have to double check.

 

[allstardentist]

keep one stationary and rotate the other three clockwise OR counter clockwise.

Interesting. Never learned that before. Thanks alot for the info.