Skip to main content
Pearson+ LogoPearson+ Logo
Start typing, then use the up and down arrows to select an option from the list.

General Chemistry

Learn the toughest concepts covered in Chemistry with step-by-step video tutorials and practice problems by world-class tutors

22. Organic Chemistry

Benzene Reactions

Although benzene rings have pi bonds like alkenes and alkynes, they cannot undergo addition reactions because of their stability and instead do Aromatic Reactions

Types of Aromatic Reactions

Understanding Aromatic Reactions

Play a video:
Was this helpful?
Hey, guys, In this new video, we're gonna take a look at aromatic reactions. So we're gonna say Although benzene rings have pi bonds just like all kinds and all kinds, they do not undergo addition reactions. That's because benzene rings are too stable. They belong to a class of compounds called aromatic compounds, and aromatic compounds don't want to do addition reactions. Now we're gonna say, instead of doing addition, reaction benzene rings as well as other aromatic compounds will instead do a substitution reaction in order to maintain their air. Metis ity. Now we're gonna say that the two major types of substitution reactions you're expected to know right now, the first one being halogen nation. So basically, in halogen nation, we're placing a halogen on benzene. But really, we're not just placing on benzene. We're switching out in H on benzene for one of the halogen, so they're basically swapping, and we're going to say, In order to do this, we have to use what's called a lewis acid catalyst. So these two things are Lewis acid catalysts. Remember, we've talked about Lewis acids before. Lewis acids are electron pair, except er's. The central element has less than eight electrons around it so it can accept additional reaction electrons. And these Lewis, as a catalyst, helped this process occur. Now you'll notice here that we're doing br to NCL, too. So when we say halogen nation, we're talking about Brahma Nation and coronation. So we're talking about br to NCL, too. Also, notice that our Lewis acid catalysts here we're using BR. So the Lewis as a catalyst has br here. We're using C L. So the Lewis as a catalyst also has CEO. They have to match each other. Now, in this reaction, all that happens is one of the hydrogen anywhere on benzene switches places with the BR. So we get here here, we can draw the double bonds anywhere we want. Because remember, we've talked about that as well. Resonance and benzene. So both will be technically the same thing. And so here we're just substituting in the halogen for the hydrogen. They got swapped. So what we just made here is bro mo benzene here. If we did see l would be the same exact thing. And it could be any hydrogen anywhere on benzene that I'm switching with the CEO, so I decided to do the top one, but I could have done it anywhere. And there goes the cl up here. And what did I make here? I make chloral benzene. So Corbyn's in would be my answer. Now that's all it iss so we're adding or substituting in a halogen in this case, B r. C. L look at how the Lewis as a catalyst match. Use br too, so you have to you f b b r three u C l two. So you have to use f B C l three Now the other major type of reaction you're expected to know Here, this is called Friedel Crafts. Friedel crafts, Al Qaeda elation. I know it's a mouthful. So here this is where an AL Kiel group is placed on bending. So Al Kiel Group switches places with the hydrogen and notice here. We're also using a Louis as a catalyst here. This Louis answer callouses, not Effie anymore. It's aluminum here in the center and notice. See how this is a C. L. So this is a CIA meaning that if that was a br, it would be lbr three. All that happens in this reaction is that the H and the AL kill substitution or I'll kill group. They switch, they swap. So we get. Now, we're gonna get this structure here. So there goes a CH around benzene. So we can say that this is called methyl benzene. That's its scientific name. But there's also a very common name for it as well. Or tall Ewing. When you have a method on bending, the common name is called Tal Ewing. Okay, so that's what happens here with Halogen Nation and freed across calculation. Now there's more than just these benzene reactions. When you get to organic to you learn more about the other ones, they're sulfa nation nitrate in. There's a lot of different reactions that benzene could do here. We're just limited to these two. So now that we've seen those two, let's see if you guys can attempt to do the this example question here. So here this is just another example of one of the two reactions we went over. Try to isolate the answer, come back and see how I approach the question. Good luck, guys.

The first major reaction is Aromatic Halogenation where a hydrogen on benzene is substituted by a halogen. 


The second major reaction is Friedel Crafts Alkylation where a hydrogen on benzene is substituted by an alkyl group. 


Determine the major product from the following Aromatic reaction

Play a video:
Was this helpful?
All right guys, let's do the example that was left on the bottom of the page. So here it says, determine the major product for the following aromatic reaction. So here we have an Al Halid. So just a carbon structure with the halogen, it's not B R two, it's not C L two. So it's not halogen. So this is Fritos alkyl and remember Fritos alkyl, the carbon group and an H switch positions and it could be any one of the hydrogens on benzene. So we get here at the end is this structure here. So you just have to draw this correctly. It's a four membered ring for car membered ring and that'd be our answer there. And if we wanted to name this, this would be cyclo because it's a substituent, but benzene, benzene forms the end of the name. So that would be the name of our structure. So again, remember that benzene is too stable to do addition, like an alkene or an alkin does. So nothing adds along their double bonds. Instead we substitute. So we replace an H with either a halogen or some type of keel group, some carbon structure and in those two ways, we get our answer. So remember, aromatic makes it too stable to react. So we have to do this. When you get to organic two, you'll see much more than just these two simple reactions. There's much more beyond halogen and Fritos alkyl. And in fact, there's another FRITO crass reaction called Asyl, but you're not gonna see it yet. So don't worry about that until you get to organic too.