R or S config?

[sam26880]

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what's the configuration of this? R or S?

CH3
|
Br-C-H
|
COOH

IF SDN formatting is messed up then please know that C is in the middle.

I thought COOH would be #1, then BR, CH3 and then H which should make this S. What do you think?

 

[Mstoothlady2012]

what's the configuration of this? R or S?

CH3
|
Br-C-H
|
COOH

IF SDN formatting is messed up then please know that C is in the middle.

I thought COOH would be #1, then BR, CH3 and then H which should make this S. What do you think?

1- Br
2 - COOH
3 - CH3
4 - H

This will give you counter clockwise configuration which is S ...but since H has a wedge you reverse the configuration...Hence its R

 

[sam26880]

hey thanks toothlady. Can you tell me why Br has a higher priority than COOH?

 

[HeatingHomer]

1- Br
2 - COOH
3 - CH3
4 - H

This will give you counter clockwise configuration which is S ...but since H has a wedge you reverse the configuration...Hence its R

How can you tell if H has a wedge? Are you referring to the fact that it is horizontal?

 

[Mstoothlady2012]

yea horizontal lines mean they are coming towards you...hence a wedge

vertical lines mean they are going into the paper..hence dashes

 

[Hysteria24]

hey thanks toothlady. Can you tell me why Br has a higher priority than COOH?

The atom with the higher atomic number has the highest priority.

C – 6
Br – 35

If two substituents are tied, then you go on and use atoms that are attached to that substituent.

Ie

In deciding between the CH3 and COOH, the COOH is a higher priority because of the O’s (atomic number – 8), than the CH3 that has H’s (atomic number – 1).

 

[Mstoothlady2012]

hey thanks toothlady. Can you tell me why Br has a higher priority than COOH?

because Br has higher atomic weight than C