# Resources on Polarimetry

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Hello all,

I have enjoyed the short time I have been on this forum reading all your questions and comments and learned a lot, having thought to myself "yes, I have had that same question as well!" I can see from the quality of the answers that there are some very smart people on here too

I want to know if anyone who has some experience with polarimetry can direct me to some good resources for learning more about its use such as an internet site or a comprehensive book. I have found many websites that give the specific rotation for many of the sugars and other compunds such as organic acids and vitamins and some general information about the theory and how to calculate concentrations and the proportions of R and S enantiomers, but I wanted to delve deeper into the subject, such as how changing the wavelength of light used will affect the optical rotation and how this can be used to obtain more information, and how changing the solvent and perhaps derivatizing the analytes (eg. methylation) can both be used to obtain more information.

More specifically, I have been reading up on the work of Fischer, Irvine and Haworth from the late 1800s and early 1900s and how they used polarimetry almost exclusively (combined with C, H and O elemental combustion analysis) to determine the structures of the different sugars and that for example maltose is a dissacharide of two glucose while sucrose consisted of one glucose and one fructose. And this was all before Mass Spec, NMR, FTIR, etc!!

I know that there methodology involved methylated the different sugars before and after hydrolysis, and from this they deduced the ring structure of the sugars and the various linkages. I just have not been able to piece together yet how they accomplished this amazing feat over 100 years ago without the wealth of such advanced instruments we have at our disposal today.

Any help in directing me towards this goal would be most appreciated! Thanks all!

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I've not had terribly much experience with polarimetry (yet), but I am quite sure there would be a number of books on the subject that would meet to your satisfaction. Where you look would really depend on how much depth you want to go and what sort of questions you're trying to answer. A good organic chemistry text book would give as much of an overview as an organic chemist needs to really know; beyond that you may be better looking into phys chem texts (not that I've ever read one). One book you may be interested in looking up is called 'Stereochemistry of Organic Compounds', by Eliel and Wilen. It's an excellent book that goes into a great deal of depth about all manner of things (I would say that your library should have a copy). During my honours year, it was the only book that gave me any kind of explanation for a particular concept I had to present on not written in French (Horeau's method, if you're curious and feeling particularly sadistic).

The relationship you mentioned between wavelength and the magnitude of optical rotation looks to be a non-linear one and gives rise to something called optical rotatory dispersion. The wiki article I just linked you states that this is used to make conclusions about the absolute configuration of inorganic substrates. For organic compounds, altering the wavelength isn't really something I've seen employed and the reason for that would obviously be one of consistency. Usually 589nm wavelengths are employed, which is denoted by D in [$\alpha$]D.

As for Fischer and co's work from the 19 and 20th century - I agree that it's pretty incredible and I've mentioned somewhere here before that I consider them to be some of the greatest organic chemists to date for their ingenuity. You should, however, be careful not to confuse relative stereochemistry with absolute stereochemistry. They were able to chemically deduce the relative stereochemistry of each of the simple sugars by building off of observations made using glyceraldehyde and working their way up in chain length. In truth, the fact that they correctly assigned the absolute stereochemical configurations of all of the simple sugars was really just pot luck.

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