Sunday, December 11, 2011

Chemistry Sunday: Introduction to organic chemistry - functional groups

We deal a lot with functional groups in organic chemistry, so I'm going to quickly go through the various types of functional groups so we can get to more stuff about essential oils! 

A functional group is "a molecular module, and the reactivity of that functional group is assumed, within limits, to be the same in a variety of molecules. Functional groups can have decisive influence on the chemical and physical properties of organic compounds. Molecules are classified on the basis of their functional groups." (Wikipedia). Okay, that made sense in a way that was not! Let's try again....

For example, we classify something as an alcohol when it has a certain molecular structure. When you see a compound called an alcohol, we know that it must have a certain molecular structure and that it will behave in a certain way. We know it will have this oxygen and hydrogen (a hydroxyl group) in the compound, which makes it an alcohol.

If you remember the post on alkanes, you'll remember that we had the one carbon with the four hydrogens attached and we called that methane. For an alcohol, for instance, we see that there's only three hydrogens attached to the carbon, then this oxygen and hydrogen in the fourth hydrogen's place! This is substitution changes the nature of the molecule. Before, it was methane (meth- meaning one, for the one carbon, and -ane because it was a carbon chain with no double bonds). Now we have methanol (meth - for one, -ol for alcohol). Methane was a smelly gas; methanol is a liquid! The substitution of the functional group of alcohol for that fourth hydrogen group really made a huge difference in the chemistry of that molecule!

Side note: The hydroxyl group appears in a ton of different molecules, so you'll be seeing it quite a bit. It's that oxygen and hydrogen you see in this picture. It's important for so many reasons, but two really interesting ones for us are its ability to increase hydrophilicity - increasing something's love for water - and increasing water's solubility! If you really want to know more organic chemistry, say hi to the little hydroxyl group and look for it in your favourite molecules!

The R in the picture indicates there's something else there - a chain of carbons, for instance - that doesn't interest us at the moment! 

Why do we care if this is a methane molecule or a methanol molecule? Because it affects how we might use it in our products. (Although we'd never use methane - too whiffy and gaseous!) 

Alcohols tend to have much lower freezing points than something like water and they can draw water from the atmosphere to itself (it's hygroscopic). If you look at our humectants - like glycerin or propylene glycol - we know that adding them to our products will lower the freezing point and make it easier to transport lotions and other things that might contain these poly-alcohols! If we poured water on the road in winter, it'd freeze. Pour propylene glycol, glycerin, even honey on the road in December and you're doing motorists a favour by keeping that patch from freezing quickly! We also know that including an alcohol in our products makes the product more hygroscopic, meaning we will get more moisturizing for our skin because we'll draw water to it. Alcohols aren't just for Saturday nights at the karaoke bar any more!

Side note: The alcohol that makes it easier to talk to boys is called ethanol. Eth- means two, an- from the alkane or chain without double bonds, and -ol from the alcohol. Take a look at that picture. You can see the last carbon has been replaced by an oxygen and hydrogen - that's what makes this an alcohol!

I know you're asking yourself how does this relate to fatty alcohols like cetyl alcohol, cetearyl alcohol, and behenyl alcohol? These are alcohols in the sense that they have the hydroxyl group on the end. We'll be talking about this more in the future, but in the meantime if you want to know way more about fatty alcohols? Click here for a great PDF on the topic!

1 comment:

Juliet said...

Thanks for this. I'm enjoying your chemistry series. I did 1st year chemistry at university but it didn't particularly interest me then. Now I'm playing with soaps and lotions it's actually relevant stuff that I enjoy reading on a Sunday afternoon!