Week 5: Dehydration of an alcohol into an alkene

The title for this post is a bit unwieldy. I'm sure this won't be the last time that happens. I am using this title because there are multiple dehydration reactions, and there are even multiple dehydration reactions of alcohols. This post is only about a reaction in which an alcohol is dehydrated to form a π-bond between the α-carbon and the β-carbon (Greek letters are one of the most important tools in all of science and without them all sorts of bad stuff would happen somehow). I know, I know. You're confused. Again. That means it's time for a picture...
Like the reactions from the previous two weeks, this involves elimination. But those reactions involved the elimination of a halogen from the α-carbon and a hydrogen from the β-carbon. This one is called dehydration because water is removed from the alcohol. Water is lost. It's dehydration. Get it? Because that's what dehydration means. And you were probably already aware of this.

I know you probably aren't paying attention. But if you have been, you may be wondering how this happens. Surely the hydrogen on the β-carbon doesn't magically fuse to the hydroxyl group and form water because it wants to. So what's going on? How do we make an alcohol do this thing? The simple answer is acid. I know. It's awesome. Chemistry is awesome. Sulfuric acid works pretty well for this. You could use some other acid for some reason I suppose. It should be a strong acid though, because I don't traffic with weak acids.

And now an exercise for the reader. I'm serious. The acid protonates the oxygen in this reaction, forming water as a leaving group. You already know about leaving groups because they've been involved in all reactions I've done for this project (the reaction of the week one, not the whole blog) so far. The mechanism for the rest is either E2 or E1. Actually, I'll tell you that it's E2 for primary alcohols (the α-carbon is attached to only one other carbon) and that it's E1 for secondary and tertiary alcohols (the α-carbon is attached to two or three other carbons). So, from that, you should be able to figure out the rest on your own. Consider it a challenge. Well, maybe not. No, I'm not just being lazy here. I really think I've given you enough information in this and the posts on elimination reactions to see what's going on here. And it occurs to me that it may be better to try to leave some things intentionally only hinted at so that one can think about them, rather than omitting them entirely or simply spoon-feeding them to my readers (which is no one, but shut up). Well, go ahead then, deduce the rest of these reactions.