Help with optical rotation experiment

[SoftMachine]

Hey folks, I am trying to design an experiment for extra credit in my first term organic chemistry class. We just learned about chirality and optical rotation and I was hoping I could use my microscope with its 360 degree polarizer as a sort of polarimeter. I played around with it today and I'm having trouble getting results.

My idea was to observe a sucrose solution, noting any optical activity with crossed polarizers, then create an invert syrup from that solution and noting any change in activity. It all makes sense to me from a chemistry standpoint but I am having trouble translating that into useable data with the microscope.

I observed a solution of 2 parts table sugar to 1 part water. I was expecting the whole slide to exhibit optical activity but the only things visible with crossed polarizers are small sugar crystals that came out of solution. The same thing happened with the invert syrup. Surely these can't both be racemic mixtures? I also viewed crystalized invert sugar compared to sucrose crystals and since they are birefringent its hard to get a sense for optical rotation.

I'd love some guidance here on how I can redesign my experiment to show evidence for the change in optical rotation between sucrose and inverted glucose/fructose. Thanks!

[patta]

You need a pretty thick layer of glucose to see the effect, as chirality is weak. Meaning, a cup or syrup. one inch thick. You won't see rotation easily on a slide with 0.1mm syrup layer.
Usually sugar is 100% glucose (one chirality), the inverted sugar is more rare.

About rotation, see this thread; sugar at post #12
https://www.microbehunter.com/microsc ... t=13077
The rest of the thread is about quartz, that does rotation too but stronger than syrup.

The thickness of sugar you need, may not fit under the microscope.
If you manage to substitute the condenser lenses with a cup of syrup, that may be cool and you can then focus with the objectives on a slide. Otherwise, you may need to remove the objective.

Or even realize our old dream of "syrup polychromatic polarization" with two cups, one of normal and the other with inverted sugar.

[SoftMachine]

That is super helpful, thank you!

[crb5]

My idea was to observe a sucrose solution, noting any optical activity with crossed polarizers

Thanks SoftMachine for the memory. Over 50 years ago tried putting some sucrose solution in a 10 centimeter long tube with glass windows at either end, and observing the optical rotation with the "lenses" from an old pair of polarized sun glasses. I included a drop of invertase solution and, after about an hour, I began to see a noticeable shift in the polarization angle. I sat up all night to see the inversion. At that point I was hooked on biochemistry and optical methods for following enzyme reactions, which became my career and I continue to play with in retirement. Good luck with your experiments.