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Current time:0:00Total duration:8:40

Naming benzene derivatives introduction

Video transcript

I mentioned in the last video that 99% of the aromatic compounds that you'll see in a chemistry organic chemistry class is either going to be benzene or molecule derived from benzene or a molecule derived from benzene so what I want to do in this video is just familiarize you with some of these molecules and how to name them so you know what you're looking at or I guess so so you could name what you're looking at so you've seen this multiple times benzene just looks like this it's a six carbon ring with three double bonds these three double bonds like that and that's it's not it's only configuration sometimes it's shown to be in residence in resonance with this form right here so the double bonds all flip around the circle like that or sometimes it's simply drawn like this and I just talked about this in the last video just to show that really neither of these configurations is exactly right that these PI electrons are just circular eight they're just they're just moving around the entire the entire ring so and sometimes you'll just have the hexagon with a circle on the inside to show that the PI electrons just floating around the entire ring now if I were to add something to the benzene ring it's pretty straightforward to name it so say I have this molecule right here this molecule right here so let's say I have that that's benzene but let's say this carbon over here it has one two three bonds if I didn't draw anything else you just assume that there's also a hydrogen here but maybe there's no hydrogen there maybe let me do this in a different color maybe you have a chlorine there well this is just Gloria chloro this is just chloro chlorobenzene chlorobenzene if that was a bromine it would be bromobenzene so pretty straightforward if let me draw it let me treat let me change it a little bit let's see how to chloro there and let's say you had a oh I don't know let's say you had a bromo over here let's say you have a bromo over there draw the bromo bromo so you could just start numbering you could actually start numbering in either place let's start with the bromine it's just a it's alphabetically in front so this would be one bromo one bromo 2-chloro two chloro benzene pretty pretty straightforward now it gets a little bit more involved the IUPAC which we know is kind of the group that named most things they tend to everything else we've seen so far they came up with a separate naming mechanism from the common names but benzene it's so ingrained in the organic chemistry computing community that all of the benzene or benzene derivative molecules they just kind of said well you know what we'll just going to use the names that everyone uses so here's a couple of common benzene derivatives so if you have this molecule right here let me if you have this molecule right here I would actually draw the PI electrons as a circle actually I'll draw it with the double bonds so let's say you have this molecule right here and over here you have noh8 right there this is called a phenol this is called a phenol so it's not called benzene anymore and if you had a molecule that look like this if you had a molecule that looked like this so just like a phenol so it's essentially it is a phenol it is a phenol but let's say you have a bromine right there what you do is you start numbering at the the group that's making this a phenol so you start numbering there one and then you get to the two so this is two bromo this is to bromo phenol to bromo phenol and unfortunately this is one of those things you just kind of have to memorize that a phenol is really just a benzene ring with an O H group another one that is probably a good idea to memorize I mean at least for me and organic chemistry the most confusing thing is when someone says the name of a molecule that it sounds like they expect you to understand but you don't understand it so it's I guess a good idea to understand as many names as possible so if you just have a benzene ring and then you just have a methyl group you just have a methyl group attached to that benzene ring this is called toe Lewin toe Lewin and once again if you had a if you had a let's say you had a let's say you had a fluorine right over there this would be one two three floor o2 to Louie NYE always have trouble saying that because one two three you start at the group that's kind of making this the toluene and so let me let me make it a little bit clearer so this would be three three floor Oh floor Oh Halloween this would all be in one word I just wrote it up here to save some space now a couple of other ones that you will see and once again as you know if you watched many many Khan Academy videos I hate memorizing things but these are just names and these aren't systematically derived the chemistry community just uses them because that's the way they for them so it is one of those things you kind of have to memorize so if you have a benzene ring if you have a benzene ring if you have a benzene ring where the functional group that's kind of defining the benzene ring is it's essentially becoming an a mean we haven't actually covered videos on a means yet and I'll do that in a future video but it's essentially it's it's replaced one of the hydrogen's in ammonia ammonia is n it let me draw ammonia ammonia has three hydrogen's and and one lone pair here we've replaced one of the hydrogen's actually there's two hydrogen's here we've replaced one of the hydrogen's with a benzene ring this type of thing you call it aniline and and allene and allene right there in the same idea if I put a fluoro here this would be two fluoro and allene so you use whatever the base molecule is and then you just name it really the way we've named a lot of things before and I'll just introduce you to two more just so that you have them under your belt so that you will have seen them before if anyone introduces them to you and they're really introducing groups that we'll study in more detail in the future but if you have a benzene ring once again so we have a benzene ring and then you have a carboxyl group and we'll talk more about carboxyl groups in the future but it creates carboxylic acid this thing right here this hydrogen it can actually be released quite easily and we'll talk about that in the future this right here is called benzoic acid benzoic acid and this name actually there is a little bit more logic to this you have the bends part for the benzene so let me make this in different colors the benzene part that gives us the bends right there and then in general whenever you have a part whenever you have a a carboxyl group like this it becomes a carboxylic acid and you tend to add the oeq acid to the end so this actually has some logical naming to it now the last one I'll introduce you to is very similar to this instead of having an OHA here we just have a hydrogen and we read haven't it would be an aldehyde so let me draw that and you could almost imagine what that's going to be called it's benzaldehyde so let me draw it so you have your benzene ring you have your benzene ring and then instead of this carboxyl group you have an aldehyde group and aldehyde group you have your carbon there's implicitly a carbon here let me make that just in case it's the first time you're seeing it you have a carbon instead of an O H group you have just a hydrogen and so once again you have a benzene so it actually makes sense to put the bends over there and then you have the aldehyde group and then you have an aldehyde group right over here so this is called a benzaldehyde or this molecule is called benzaldehyde bends aldehyde and we'll study will study a means and aldehydes and carboxylic acids in much more detail in future videos and actually see reactions that involve them but I just wanted to expose you to this and when you see these things so when you see these kinds of names you don't you know become intimidated