Why is S-Ethyl 3-hydroxybutanoate SO MUCH more stable than its R enantiomer?

[ericvon11]

The boiling point for R-ethyl 3-hyrdoxybutanoate is about 75 C
The boiling point for S-ethyl 3-hyrdoxybutanoate is about 180 C

How!?
How is the same molecule that much more stable just by rearrangement of the hydroxy group. I'm trying to explain how some R enantiomer may boil off along with ether if heated enough but I'd like to explain why it is that the R enantiomer is less stable

 

[Nemus]

This must be wrong (the spelling of the substance name is also wrong by the way). Enantiomers have the same boiling point under normal conditions. Were it true you'd have a wonderful business opportunity separating the enantiomes and selling them. I checked the data at Sigma Aldrich and I suspect that is where you have got your data because I find the same odd difference. The racemate is stated to have a bp of 170 oC so the higher value is probably true.

 

[ericvon11]

Woops! I meant hydroxy. Hm, maybe I read this was under pressure. My lab book says 180-182 for the s enantiomer. I'm still confused as to why the re face of ethyl acetoacetate is so much more favorable in my reduction reaction using alcohol dehydrogenase. Any clue?

 

[Nemus]

Yes, with the dehydrogenase it has nothing to do with stability. It is related to the lack of symmetry in the enzyme active site. If I remember correctly there are some rules of thumb to predict which enantiomer that predominates for a new substrate but the thumb of those rules tend to be rather thick so often you get what you get.
At pdb there are lots of structures here is a relevant one showing an inhibitor bound to the active site: http://www.rcsb.org/pdb/explore/explore.do?structureId=1AXE

 

[ericvon11]

cool, that helps. Basically, I've taken it that the reason why I got 92 percent S in this reaction of yeast alcohol dehydrogenase and acetoacetate is because NADH can only donate to the acetoacetate from one side that fits (the S). And the small amount of R would likely be from induced fit model meaning that the enzyme changes to fit some si faced acetoacetates making R enantiomers. This however must take longer than the S and thus is less. Does that sound right, to your knowledge?
Edit: Fits from one side (re face creating an S)

 

[Nemus]

Exactly!

 

[ericvon11]

Thank you so much. I've been trying to explain this lab for the entire day and couldn't quite get it. I appreciate the help!