How Do You Correctly Draw Enantiomers of Ibuprofen?

[cdotter]

Homework Statement

Draw the two enantiomers of ibuprofen using the correct dash and wedge bonds.

Homework Equations

(I was given a flat molecule like the one above.)

The Attempt at a Solution

I put a wedge from the asymmetric carbon to the hydrogen and a dash from the asymmetric carbon to the ring. My professor drew it as a wedge from the asymmetric carbon to the hydrogen and a dash from the asymmetric carbon to the methyl group. Is his way the correct way or does it not matter?

 

[chemisttree]

Draw it one way and it is the R enantiomer. Draw it the other way and it is the S enantiomer. The question asks you to draw BOTH and label them correctly.

You haven't done the problem yet.

 

[cdotter]

I drew it both ways.

Wedge from the asymmetric carbon to the hydrogen and a dash from the asymmetric carbon to the ring; dash from the asymmetric carbon to the hydrogen and a wedge from the asymmetric carbon to the ring.

He marked it partially wrong and drew it

Wedge from the asymmetric carbon to the hydrogen and a dash from the asymmetric carbon to the methyl group; Dash from the asymmetric carbon to the hydrogen and a wedge from the asymmetric carbon to the methyl group.

Why is his way the more correct way?

 

[chemisttree]

Ibuprofen is a racemic mixture of both isomers. The active form is the S enantiomer. Were you supposed to know that or was it given in the problem?

Do you know the rules governing the R and S designation?

 

[cdotter]

So it shouldn't matter where the wedge/dashes go as long as the priorities are in the correct decreasing order for either R and S? Sorry for not just posting what I drew but I don't have a scanner and I can't find any online molecule drawing software. :(

 

[chemisttree]

That's how I would grade it. Remember that the rule is to put the lowest priority dashed and then trace the remaining groups according to priority. Clockwise is R, counterclockwise is S. The configuration you determine is reversed from that when you switch any two groups.

http://bkchem.zirael.org/"

 

[sjb-2812]

I don't think it really matters in the grand schem of things, but it can start getting messy if you draw wedges and hashes attached to a ring atom. In some cases of course this is unavoidable.

 

[cdotter]

[PLAIN]http://img179.imageshack.us/img179/6450/19079153.png

I drew the one on the left. My professor drew the one on the right.

I believe mine is the S enantiomer?

 

[chemisttree]

for your structure, the lowest priority group is wedged. It's OK but you need to keep in mind that the lowest priority substituent must be dashed for you to determine the configuration (clockwise = R for example). In your example, rank the substituents around the chiral center (include the hydrogen) and tell me your rationale for the S determination, please.

Are these the same molecule? I believe they are and your professor should not have counted your answer incorrect or partially wrong. By convention, the lowest two groups are dashed/wedged as your professor has shown but it isn't a hard and fast rule.

 

[cdotter]

for your structure, the lowest priority group is wedged. It's OK but you need to keep in mind that the lowest priority substituent must be dashed for you to determine the configuration (clockwise = R for example). In your example, rank the substituents around the chiral center (include the hydrogen) and tell me your rationale for the S determination, please.

Are these the same molecule? I believe they are and your professor should not have counted your answer incorrect or partially wrong. By convention, the lowest two groups are dashed/wedged as your professor has shown but it isn't a hard and fast rule.

Lowest to highest priority: H, CH3, ring, COOH. Originally I drew it with hydrogen having a dash and the ring as a wedge. But that would make it the R enantiomer. I want the S, so I flipped the dash/wedges around and got the molecule on the left.