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Current time:0:00Total duration:8:44

Video transcript

in the last video we learned a little bit about aldehydes about aldehydes and we saw that they had the general structure where you have a carbonyl group bonded to some type of carbon chain or I guess in the simplest form this could just be a hydrogen over here and then they definitely will have at least one hydrogen bonded to the carbon in the carbonyl group so this was an aldehyde now very closely related to an aldehyde is a type of molecule called a ketone and let's draw a couple of ketones just to make things clear and then we'll think about what the difference is between a ketone and an aldehyde so this right here ch3 ch3 carbon right over here we this right here is a ketone and you say hey Sal that looks very similar to an aldehyde I have a carbonyl group in both so this right here is a carbonyl group this right here is a carbonyl group let me write this car carbon eel we have a carbonyl group in both we have a carbon chain over here this could be a general carbon chain here we have a methyl group so how is this different and I think you'll see it's this part that I haven't highlighted yet in an aldehyde there's two ways to think about an aldehyde you could either say that look the carbonyl group is at the end of a carbon chain so the next thing over is going to be a hydrogen or you could say that in an aldehyde you have at least a one hydrogen bonded to the carbonyl carbon and the way I remember that so you have a hi you have a hydrogen there and in the ketone you don't the carbonyl group is embedded in a carbon chain it is bonded to at least is bonded to a carbon on either side so over here you have a carbon and the way that I remember the difference and this is really just a little bit of a mnemonic just to memorize it is aldehyde has an H in it aldehyde has an H in it there's an H right over there and an aldehyde has a hydrogen bonded to this carbon so now that we at least have a reasonable understanding of what a ketone is let's name a few just to familiarize ourselves so this right here is the simplest possible ketone and it's called acetone that's its common name it is called acetone and actually the word ketone comes from the german word for acetone which was i think instead of a c there they had a k' so it's like a cotone and they said oh this is a ketone so this is a common name another kind of traditional or common way of naming acetone and we'll see or of naming a ketone is to name each of these groups and it's kind of it's similar to the way that we named ethers but instead of writing the word ether at the end we write the word ketone so here we have a methyl group and we have another methyl group so this would be so we have two methyl groups right over here so this would be dye dye methyl dimethyl ketone this right here is dye methyl ketone and then if you wanted the systematic way of naming it you just look at the longest carbon chain which is one two three carbons so it's probe propa and instead of calling it propane we get rid of that a over there and we'd call it propanone we could call it propanone that tells us that this right here is a ketone and you have to know where this double bond and actually four propanone you don't have to specify it because if you know it's a ketone you know that it has to have a carbon on either side of the carbonyl group so you actually don't even have to specify where the carbonyl group is but if you wanted to you could say okay that's going to be on the two carbon no matter what direction you start counting from it's going to be on the two carbon but the two is kind of optional for propanone the two is optional for propanol let's do a couple of other ones so let's say we had let's say we had a molecule that look like this let's say we have a molecule that looks like this so the traditional way of naming it you'd say okay on this end of the ketone i have one two three carbons so on that end i have three carbons that is a propyl group that is a propyl group and on this other side of the ketone right over here i have only one carbon that is a methyl group that is a methyl group so then you would just name them when you name them in order of increasing chain size or carbon just or or Argus molecule site or group size so this would you write methyl first methyl because it's only one carbon so it's this is methyl propyl methyl propyl methyl propyl ketone methyl propyl ketone this is kind of the traditional or the common way so often kind of the most used way of naming this molecule but the systematic way of naming it you look at the longest carbon chain and you say okay I have one two three four five carbons so it's going to be pent and then you want to start numbering it so that the ketone carbon or the carbonyl carbon I should say has the lowest possible number so you want to start numbering on the right side 1 2 3 4 & 5 so this right here so we said the prefix would be pent so it's pent tun and instead of saying it's pentane you say it's pentanone Penta Penta known and to specify where the carbonyl group is you say it's - this is - pentanone and you might also see it written like this you might also see it written as Penta Penton Penton - 2 own either one of these right here would be acceptable let's do a slightly more complicated example let's say we had something that looked like this so we have something a molecule that looked like this let me stick some chlorines over here so what would this be well our longest chain once again is this cyclohexane 1 2 3 4 5 6 carbons I'll just name this systematically right here and the more complicated things get the more systematic people will want to name it so if we have six carbons right here and they're in a chain so this is cyclo cyclo hexane you would put the e there if this was just and this was if this carbonyl group wasn't there but since it is we would call this cyclohexanone so this right here tells us to name it cyclo hexa known and then you know in a ring like this this would implicitly be the number 1 carbon so this is the number one carbon and we're going to we're going to we want to number in the direction so that the next groups have the lowest possible number so we want to make this the two carbon so this is to to die chloro cyclohexanone so this is to to die chloro dichloro cyclohexanone now there's two more and I'll just show these to you because these are tend to be referred to by their common names so I just want to show them to you real fast one is this molecule right here where we have a methyl group on this side ch3 and over here we have a benzene ring we have a benzene ring over here now that first super simple ketone that we saw we call this acetone and so the common name here is actually driven from acetone instead of calling it acetone because it doesn't have just a methyl group here this is called this is called acid acid tow and instead of acetone its acetophenone because we have this phenyl group that benzene ring right there acetophenone which is a pretty common molecule you'll see and you'll see it referred to this way now the other the other one that you might see every now and then i just want to expose it to you is a molecule that looks like this that has two benzene rings on it so it has two benzene rings on it looks like that and this is benzophenone benzo benzo vino these last two I just really wanted to expose you to their common names but in general I think you have a decent idea at this point of how to name at least the simpler chains either with the common names for example propyl or methyl propyl ketone or two pentanone and these are these are kind of the more typical or maybe the easier naming examples