# Will table sugar twist polarized light?

I recently saw this awesome video by Steve Mould where he explained that a sugar solution in water will turn polarized light in the clockwise direction.

The explanation basically boils down to sugar molecules (glucose) having a handedness (they are chiral) and that linearly polarized light can be thought of as a superposition of circular polarized light in opposite directions which experience a different refractive index when interacting with the sugar solution.

Now to my question; If I want to replicate this experiment at home, will regular table sugar work, or do I need pure glucose, and if that is the case where can I get it?

Many thanks!

Edit 1: I will get back with the results I get from using table sugar when I have performed the experiment.

Edit 2: I did the experiment using half water half sugar, basically simple syrup, and the result was excellent. The optical rotation was very apparent.

• Just beware of the table sugar being used by Jules Verne Durand & his gang :-) Commented Aug 25, 2020 at 11:24
• Re, "where can I get it?" Have you looked? When I typed "pure glucose" into Google, I got some promising results. Commented Aug 25, 2020 at 13:21
• en.wikipedia.org/wiki/Inverted_sugar_syrup - it is called inverted because the mixture (glucose and fructose) rotate the polarization in the opposite direction compared to the sucrose solution one starts with. Commented Aug 25, 2020 at 19:19

Chemically, table sugar is sucrose, whose molecule is basically a unit of glucose and a unit of fructose connected together. To know the expected amount of rotation of polarization for a given substance, see the table of specific rotations.

In particular, for D-glucose specific rotation is $$+52.7°\,\mathrm{dm}^{-1}\,\mathrm{cm}^3\,\mathrm{g}^{-1}$$, while for D-sucrose it's $$+66.37°\,\mathrm{dm}^{-1}\,\mathrm{cm}^3\,\mathrm{g}^{-1}$$, which is actually even larger than that of D-glucose. So yes, you should be able to succeed with the experiment using table sugar instead of glucose.

• Thanks! My initial guess was that since sucrose is made up of glucose and fructose, and fructose rotates polarized light in the opposite direction of glucose that the net effect of the twisting of polarized light for sucrose would be zero. Commented Aug 25, 2020 at 9:38
• @Turbotanten well, they rotate by different amounts, so even if the net effect were a simple addition, you'd still get something nonzero. Commented Aug 25, 2020 at 9:43
• Yes that's what I figured! :) Commented Aug 25, 2020 at 9:43
• @Turbotanten optical rotation has a tendency to be nonadditive once new chemical interactions are involved. This has led a lot of difficulty in computational prediction of OR for solutions as you can't simply determine the OR of the molecule and the OR of the surrounding (chiral) solvent cavity separately. Commented Aug 25, 2020 at 21:31
• dm^-1? what is this unit? Commented Aug 27, 2020 at 4:22

I have successfully done this demonstration in my classes using table sugar. I place a polarizer on an old-fashioned overhead projector, hold a crossed polarizer above it to block the light, and then insert a beaker of sugar solution between the two. I usually use a solution of 1:1 sugar-to-water (by volume), basically a "simple syrup"; and I use a column depth of about 10 cm or so.

If I remember correctly, the transmitted light has a distinct bluish color when you do this, which I assume is due to the frequency dependence of the specific rotation.

• Also, I'm amused that this question has given me (a theorist) a chance to post an "experimental" answer. Commented Aug 25, 2020 at 17:32
• The coloration is an interesting detail I didn't even think to think of :) Commented Aug 25, 2020 at 17:32
• Exciting! I have, over the past year, often found myself lamenting how hard it is to find overhead projectors these days. They are very useful for undergraduate demonstrations... Commented Aug 25, 2020 at 17:48
• @Philip: I think I've also successfully done this demo using a document projector with a backlight. But I don't know how many document projectors have this feature. Commented Aug 25, 2020 at 18:57

Yes, I helped my daughter do this demonstration for her sixth grade science project. She used plain table sugar and a laser pointer as the light source. Having a monochromatic source makes it a little clearer. If you have different color laser pointers it would be interesting to demonstrate wavelength dependence.