Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Optical Isomers

  1. Nov 5, 2005 #1
    Hi all. It has been a while since I last posted.

    I was reading a couple of days ago about optical isomers. I found that L-type isomers cost more than D-type isomers, to manufacture and sell. I was wondering if anyone knew why?

    Because of the new rules on PF, I am going to state what I think. I think it is because D-type isomers occur in nature and do not have to be designed, manufactured and sold the way L-types do.

    However I am unsure and hope for some help on this topic.

    The Bob (2004 ©)
  2. jcsd
  3. Nov 5, 2005 #2
    Hmm... all L-type isomers are more expensive than the D-types ?

    I'm not sure you can generalize that far...:shy: (I'm no stereochemistry expert, although I do find stereochemistry to be the easiest of all organic chem topics :rolleyes:, not that I actually studied the various costs and prices)
    If you do notice a signficant trend--->that D-type isomers are "significantly" more abundant than L-types in nature-->try posting this in the biology forum:

    *What naturally/biologically favorable advantage do dextrorotatory (i.e., D-type) molecules have over their leuvarotary (L-type) counterparts?

    *Or, what else makes them more abundant in nature?
    Last edited: Nov 6, 2005
  4. Nov 6, 2005 #3


    User Avatar
    Science Advisor

    It's actually not true. The natural amino acids are all D, but natural form of tartaric acid is L. The D/L nomenclature is kind of antiquated. It was determined based on the relation to glyceraldehyde, which was arbitrarily assigned as D for the natural form. However, the relation to glyceraldehyde was based on degradation of the molecule you were trying to relate, so it was very dependent on how you degraded the molecule.

    I think that they may actually synthesize all of the amino acids that you buy through enantioselective reactions, so the two enantiomers are relatively similar in price most of the time. The difference might instead be due to the higher demand for the natural enantiomer and differences in the cost of the two enantiomers of the catalyst used to make the amine acid.

    In principle, the D enantiomer has no advantage over the L enantiomer until it comes into contact with another chiral molecule. It just so happens that to get our bodies to work right, we need all D amino acids. In principle, if we used all L amino acids there wouldn't be any noticeable difference. I think the prevailing theory on why we got D and not L is that D was for some reason more available when life was first developing.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook