A while back we made a post on Facebook about how lemons and oranges get their distinct smells from a molecule called limonene.

This molecule comes in two different chemical arrangements which are mirror images of one another.

One type of limonene is responsible for the lemon scent and the other for the orange scent.

Pretty neat huh?

Yeah, except for the part that it's like totally bogus.

Big thanks to our friend Sandra Koster who spoke up and called us out.

We felt pretty sour about publishing such a tasteless myth, so we decided it's time to set the record straight on limonene.

Limonene is an enantiomeric molecule.

Enantiomers have the same chemical formula but a different 3d arrangement of their bonds.

The molecules are actually mirror images of one another that cannot be superimposed, kind of like our left and right hands.

Chemists refer to these mirror image molecules as R and S enantiomers.

This myth that we found everywhere claims that orange oil has one limonene enantiomer that smells like oranges and lemon oil contains the lemon scented mirror image molecule.

This is completely false.

As it turns out, oranges and lemons each have both of these molecules.

Except the overwhelming majority of the limonene, 96 to 99 percent, in both cases, isn't the R configuration, and only one to four percent is in the S configuration.

So what exactly do R and S limonene smell like?

In high purity they both actually smell pretty strong.

S limonene even has a slight lemon scent to it, but it's not fully responsible for the fragrance of lemons.

Rather, there are a host of other different compounds that work together to give both lemons and oranges their own distinctive aromas.

Here are just a few of the many hundreds of contributors.

So if the limonene and enantiomers don't explain the difference between orange and lemon scents, how then did this myth get started?

A team of Australian flavor chemists traced it all the way back to a 1971 paper published in the journal Science.

This paper attributed lemon scent to S limonene from lemons and orange scent to R limonene.

Then that paper got cited by other papers, which got cited by textbooks, and from there the misconception found its way to the Internet.

So why is this so easy to believe and how did it become so pervasive?

First off, some enantiomers actually do smell different.

For example R carvone smells like spearmint, whereas the enantiomer S carvone smells of dill or caraway.

It's easy to assume that other enantiomers might also smell different from one another.

Secondly, it's really easy to muddy the smell study waters so to speak.

Odor is something that's really tough to experiment with and understand.

You have to make absolutely sure that the compound you're analyzing is 100% pure.

Even tiny impurities can have a big odiferous impact.

For example, the R version of this compound has a powerful potato aroma.

Its enantiomer is odorless.

But if your sample of S enantiomer was contaminated with as little as 0.1% of the smelly R enantiomer, you'd probably think both smelled of potatoes.

Our sense of smell can also be very subjective.

Something that smells floral to one person could have citrusy notes to another.

Plus, we're all subject to the power of suggestion.

In the end, this tale of two enantiomers highlights just how easy it is for misconceptions to spread.

But you know what?

That's what sets Reactions apart from the crowd.

When we spread a myth we go out of our way to bust it too.

And though it may seem like common sense, this was a good opportunity to remind us and you it's always a good idea to double-check source material to make sure it holds up.

Thanks for watching.

If you want to learn even more about how enantiomers can smell different, check out this Get to Know a Molecule about the sweet scent of