[Marshall_969]

Hey Guys im new here and this is my first post. Im sitting a test this year for medicine and am revising my O chem.

Hope you can help with this question.

I have a book here which has a picture of lactic acid and clearly states its in the S config.

For the life of me i cannot understand how?

I shall explain the picture now. It doesnt make it any easier that i have forgotten whether solid triangle and dash triangle which is into page and which is out pf page, so could somebody please tell me which is which as well?

Picture is as follows C in the centre. Dashed triangle to the top (CH3). Dashed triangle to bottom (COOH). There is a H on the left side with a solid triangle. OH on the right with another solid triangle.

MY working is this OH is priority one, COOH =2 CH3 =3. 1 ( on right) to 2( down bottom), skip the H to 3(up top). This is clockwise and thus im sure its R config???

Unless the into and out of page changes it???

Cheers

[discodermolide]

Hey Guys im new here and this is my first post. Im sitting a test this year for medicine and am revising my O chem.

Hope you can help with this question.

I have a book here which has a picture of lactic acid and clearly states its in the S config.

For the life of me i cannot understand how?

I shall explain the picture now. It doesnt make it any easier that i have forgotten whether solid triangle and dash triangle which is into page and which is out pf page, so could somebody please tell me which is which as well?



Picture is as follows C in the centre. Dashed triangle to the top (CH3). Dashed triangle to bottom (COOH). There is a H on the left side with a solid triangle. OH on the right with another solid triangle.

MY working is this OH is priority one, COOH =2 CH3 =3. 1 ( on right) to 2( down bottom), skip the H to 3(up top). This is clockwise and thus im sure its R config???

Unless the into and out of page changes it???

Cheers

The book seems to be correct, remember the group with the lowest priority should point away from you. And judging by what you said above I would check that you got the priority correct.

[Dan]

Unless the into and out of page changes it???

Yes, it does.

If the lowest priority substituent points away from you, then clockwise is R and anticlockwise is S.

If the lowest priority substituent points towards you, as you have described for your case, then clockwise is S and anticlockwise is R.

If "clockwise is R and anticlockwise is S" was always true, then a compound's R/S label would change depending on the viewing angle and be meaningless.

[Doc Oc]

I shall explain the picture now. It doesnt make it any easier that i have forgotten whether solid triangle and dash triangle which is into page and which is out pf page, so could somebody please tell me which is which as well?

Solid wedges indicate the bond is coming out of the page towards you, dashed wedges are into the page away from you.  I always recommend that people make models to help themselves understand stereochemistry.

The book is correct in the assignment, and if you make a model you will be able to see it.