Don't panic if you don't get this the first time around. There is time to learn it more carefully, later. But.....
Some of my dear readers were introduced to polarimetry on Friday. A hallway conversation after the lab involved two isomers of the type that can be distinguished by their rotation of plane-polarized light. Both compounds are recognized by us for their tastes. They are the (+) or dextrorotatory isomer called R-carvone and (-) or levorotatory S-Carvone.
Both share the same connectivity and the same molecular formula and while both contain several double bonds, they are not geometric "cis-trans" isomers of one another.
The dextrorotatory isomer is a major substituent in caroway, and is also present in some quantity in dill and in the peel of mandarin oranges. Which I love, by the way. Which are in season, by the way. Get them now because they are seasonable! consider it a chemistry research project.
The levorotatory isomer is a major oil in spearmint. Yep, that's different than caraway or dill, in my book. I have heard however that some people are unable to distinguish between these two substances.
That's a curiosity to me, since the proteins that mediate our chemical senses...smell and taste....are almost always themselves able to clearly distinguish these types of isomers.
These substances are also great examples of terpenes, which I'd love to describe but will have to save for another post.
As always, there is more you can read at Wikipedia.