Constitutional Isomers Redux

I suppose that my textbook introduces constitutional isomers in the alkanes chapter because alkanes are pretty straightforward and can ease one into the concept. Constitutional isomers can and do occur in other molecules. Isomerism is when two or more different compounds have the same molecular formulae. In other words, they have the same kinds of atoms and the same numbers of those atoms, but something makes them chemically distinct. Later on, we will explore stereoisomers, and it will be very exciting. But for now, we're looking at constitutional isomers, which differ in the way the atoms are connected to each other. Let's take a look at two molecules that are constitutional isomers of each other...

Name: n-butane (or just butane)
Molecular formula: C₄H₁₀
Condensed structure: CH₃CH₂CH₂CH₃
In stunning 3-D:
Yes, I just figured out that I could render butane three-dimensionally with my nifty software. Anyway...

Name: isobutane (or 2-methylpropane)
Molecular formula: C₄H₁₀
Condensed structure: CH(CH₃)₃
In glorious 3-D:
Both molecules have the same quantities of the same atoms. But the bonds are not identical here. A carbon bonded to two other carbons and two hydrogens is electromagnetically different from one bonded to three other carbons and one hydrogen. Also, the three-dimensional forms are quite different, and when the molecules interact with other bodies (including other molecules just like themselves) the results will be at least slightly different. Although very similar, these two compounds have different chemical and physical properties. They are more like each other than other compounds that have different atoms and other, more striking differences. Because of these facts, we use the term "constitutional isomers" to denote the relationship between these similar molecules.

But when it comes to properties, constitutional isomers are not always so similar to each other as those two. Some constitutional isomers contain different functional groups from each other and, if you remember the importance of functional groups like you should, this means they can have dramatically different chemical and physical properties...

Name: ethanol

Molecular formula: C₂H₆O

Condensed structure: CH₃CH₂OH

In brilliant 3-D:

It's an old friend: ethanol. I don't know how many times I've shown ethanol before, but you had better know that this is what it looks like. And if you managed to actually have some brain capacity, maybe you even remember that this compound is an alcohol, as it has a hydroxyl functional group. Easy, but here's a constitutional isomer of ethanol.

Name: dimethyl ether (or methoxymethane)

Molecular formula: C₂H₆O

Condensed structure: CH₃OCH₃

In spectacular 3-D:
Since the name has "ether" in it, you have deduced, unless you are a total idiot, that this is an ether (the name of the functional group is methoxy in this case). But the molecular formula is the same. The functional groups here are so unlike each other that reactions possible for one would be impossible for the other. Oh, and remember hydrogen bonding? Ethanol has it. Dimethyl ether cannot have hydrogen bonding because there is no hydrogen attached to the oxygen, so these two even have different intermolecular forces. In this way, two constitutional isomers can be quite dissimilar. What kind of atoms a molecule has and how many are very important, but the configuration of the bonds holding the atoms together in a molecule matters a lot too.

Edit: After posting this, I started going back to tag my posts. I noticed that way back in February, I wrote a post about constitutional isomers. I think this new post is better, but here is the old one. If you do not get the concept after reading this post, read the old one. If you still don't get it, tell me, I guess. It seems fairly simple to me and I think I did an adequate job of explaining it both times, but maybe I am wrong...