The difference between saturated and unsaturated molecules

The difference between saturated and unsaturated molecules


Hey, guys, so now we’re going to talk about
a topic called index of hydrogen deficiency and this is a topic that usually isn’t covered
in the first chapter of most textbooks. So, you’re probably thinking, “Johnny, why
are you teaching this to me if I don’t need to know it yet?” Well, because there’s this other topic called
constitutional isomers and that topic is much easier to understand if you already know the
IHD rules. So what I’m going to do here is I’m going
to jump a little bit forward and teach you something that you don’t need to know yet
because it’s going to make isomers so much easier to understand for this chapter. Let’s go ahead and begin. There’s actually two different ways to compute
the IHD and that is one structural and the other one is with molecular formula. What I’m going to do on this page is just
show you the structural one which is actually the easier one and then we’ll move on to molecular
formula. First of all, let’s just talk about what is
index of hydrogen deficiency. Well, what it has to do with is how unsaturated
or saturated a molecule is. So what’s that word saturated? Well, a saturated molecule is any molecule
that has as many hydrogens as possible. And there’s this formula that we can use in
all chemistry to figure out if it has as many hydrogens as possible. And that formula is – maybe you remember
it from gen chem – it’s 2n plus 2, where n is equal to the number of carbons. So I have my 2n plus 2 rule. What that’s going to do is it’s going to predict
for me how many hydrogens I need for my structure for it to be fully saturated, meaning that
it has as many hydrogens as it can possibly hold. Any molecule that has less than that number,
2n plus 2, is going to be considered to be unsaturated. These are words, saturated and unsaturated,
they might sound familiar to you. That’s because these are words we use actually
in cooking. Saturated fat would actually be a fat – fats
are these long carbon chains – it would be this fat that has as many hydrogens as
possible. An unsaturated fat would be one that’s missing
a few hydrogens. So you might be wondering, “Okay, Johnny,
what makes carbons miss hydrogens? Why would you be missing some?” It turns out it only happens for two different
reasons. I’m going to write this down. It happens for pi bonds. Remember that pi bonds just have to do with
double bonds or triple bonds. They both have pi bonds. Then also, rings. Rings are also going to take away some of
the hydrogens from a molecule because what that means is that one of the ends is supposed
to be CH3 and the other end is supposed to be CH3, but when you make a ring, they have
to fuse together so that means that now you have to make them CH2’s. What I’m trying to say is that a ring actually
takes some hydrogens away from the carbon structure.

2 Replies to “The difference between saturated and unsaturated molecules”

Add a Comment

Your email address will not be published. Required fields are marked *