[curiouscat]

Without  resorting to experiments, is there a theoretical way to predict the specific rotation of a given optically active molecule? Even in an approximate sense how is the amount of rotation a molecule produces related to its structure? Compounds seem to have such a wide range of specific rotations and I am a bit mystified in how this relates to their structure.  If not a theory are there any heuristics or group contribution methods to quantitatively predict specific rotations?

Also, could a molecule be so optically active (i.e. rotate the plane of polarization so much) that it returns to its starting rotation plane; i.e. zero. In other words, could a given sample of an optically active compound effectively appear inactive through a polarimeter? Is polariometric activity a sufficient but not necessary condition of optical activity?

[helenn]

As far as understand optical activity cannot be predicted and there isn't any relation to the number and structure. My PhD was a natural product synthesis and the fragment I was synthesising had a chiral centre. There was no pattern to the optical activity through the synthetic sequence and the sign changed as well.

[curiouscat]

Thanks! It does seem odd to me that we have made no theoretical inroads at all in predicting anything about the specific rotation.

[Borek]

That's not exactly true. There was plenty of work published on the subject. Which doesn't mean it is an easy task. As is often the case, it is much easier to prepare the substance and measure its properties, than to predict them from calculations.

Here are some links - sorry, they were part of a larger discussion elsewhere and I have no time to dig through them to find out which ones are the best.

Lecture on the optical rotation:
http://www.cosmolearning.com/video-lectures/preparing-single-enantiomers-and-the-mechanism-of-optical-rotation-6675/

Paper on the Drude helix model:
http://www.sciencedirect.com/science/article/pii/S0301010406004915

Paper on predicting the rotation for some polymers:
http://jcp.aip.org/resource/1/jcpsa6/v38/i6/p1317_s1?isAuthorized=no

[NotExactly]

You can use quantum mechanics to predict the optical rotation of molecules as well.  Try asking a physical/computational chemist.

[curiouscat]

Thanks for those leads Borek! Very interesting reading indeed.