If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:13:32

Common and systematic naming: iso-, sec-, and tert- prefixes

Video transcript

let's see if we can get the molecular structure for butyl butyl cyclo cyclopentane so you would just break this up the way we've done it in the last several videos it is a the suffix is Ain so it is an alkane all single bonds so single single bonds it's pentane so we're dealing with five carbons on kind of the base or on the kind of the backbone so this is five carbons and it's a cyclopentane so it's five carbons in a ring so it's five carbon ring is the backbone and then we have a butyl group added to that five carbon ring now you might say hey Sal how do I know which carbon to add it to when you're dealing with a ring and you only have one group on the ring it doesn't matter because let me just show you what I mean so let's draw the five carbon ring let's draw the cyclopentane so it'll just be a Pentagon so one two three four five and then you it's a ring so you can connect them one two three four five now it doesn't matter where I draw the butyl group it's all symmetric around there we just have a ring and it's connected to a butte a butyl group at some point it'll start to matter once we add more than one group so we can just pick any of these carbons to add the butyl group to now just as a review the butte prefix that refers to remember methyl ethyl propyl or meth f probe butte this is four carbons this is a four four carbon alkyl group so let me just add it here I could have added it to any of these carbons around this cyclopentane ring so if I just add it right here so I'm going to have four carbons so one two three four that is the butyl part of this whole thing and then let me just attach them up so you might be tempted to just draw this right there and actually this would be right this is butyl cyclopentane but a question might rise I just happened to connect the cyclopentane to the butyl at this first carbon on the butyl right there I could have just as easily done it like this I could have just as easily had a I could have just as easily had it like this where let me draw my butyl again so I have one two three four so once again this is a butyl but instead of instead of being bonded to the cyclopentane on my first carbon maybe it's bonded right here maybe let me do it with that yellow color maybe it's bonded right here why this seems like maybe this could also be butyl cyclo pentene it looks like we have a butyl group this is butyl right here I drew a butyl group right over here and I also draw a butyl group right over here but these are fundamentally two different molecular structures I'm touching the first carbon here I'm touching the second carbon over here now there's two ways to differentiate this one is the common naming and one is the systematic naming so let me differentiate between the two so in the common naming and this can get a little bit involved and this frankly is probably the most complicated or a part of naming organic compounds systematic is often more complicated but it's easier to I guess systematically come up with it so there's a common and then there's a systematic systematic systematic so the common way of doing it is if you just if you just say butyl cyclopentane that implies that you are bonding to the first or depending on you the last carbon in the chain so this right here is butyl cyclopentane this right here is not just butyl cyclopentane what you would do is you definitely have a cyclopentane ring so this would definitely be a cyclopentane cyclohexane cyclopentane and you do have a butyl group on it so we do have a butyl group a butyl group but because we are bonded we aren't bonded to the first carbon we're bonded to a carbon that is bonded to two other carbons we call this sec-butyl cyclopentane SEC let me so this is SEC and everything I'm doing is obviously freehand if you were to see this in the book the SEC would be italicized or sometimes it would be written as s as s butyl s butyl butyl cyclopentane cyclohexane that is touching two other carbons so you look at the butyl group and say well which of these carbons attached to two others it's either that one or that one and regardless of whether you're attached to this or this you think about it it's fundamentally the same molecular structure so that's what you do when you're attached to that guy right over there but what about the situation we're dealing with just the common names right here what about the situation where it looks like this so we have our cyclopentane right there and we have a I guess we could call it a butyl group it'll have four carbons in it but let's say that the four carbons look something like this let's say our four carbons so we have one two three four one two three four carbons and we're bonded to this one right over here so whenever you're bonded to I guess one end of the four carbon group and it branches off at the other end and it seems a little complicated this only deals four alkyl groups below really five or six carbons this we call an isobutyl group so let me write this down so this is this right here is SEC beetle or s butyl sometimes for short this right here this right there is isobutyl I so it's actually I so that is an isobutyl group and then the last thing to worry about when you're dealing with butyl groups is something like this is something like this so let me draw it so you could also draw four carbons like this you have one carbon one two three four one two three four carbons and you're attached over here now this naming this group this group right here you're going to see the systematic naming is much easier for these compounds this group right here over here that the carbon you're attached to is attached to two other carbons so it is sec-butyl when you're attached to three it is t-butyl or tert-butyl so this right here is a tert tert tert-butyl group or sometimes called a t-butyl and i really want you to understand the difference here the common naming it's easier to say and easier to spell but it's sometimes a little confusing this is just straight-up butyl so you would call this butyl cyclopentane this is sec butyl because you have this guy's connected to two carbons that's where the sec comes from that's where the sec comes from sometimes it'll be s butyl so this could be called sec-butyl sec-butyl cyclopentane or s butyl cyclopentane this because we're attached to the end way from this branching off is still a butyl group since we have four carbons but since we're attached here this is isobutyl so this is isobutyl cyclopentane and then finally since the carbon we're attaching to is attached to one to three other carbons it is it is a tert-butyl or a t-butyl group so this is T butyl cyclopentane that's the common naming so maybe I should clear out systematic here just so it's clear to you just so it's clear to you that everything we've done here is common naming is common naming so let me write down it won't hurt to write them down again because I'm more familiar with you are with these the better so this is just butyl butyl butyl cyclo pentene this is s or sec butyl sec-butyl cyclopentane and this is iso isobutyl butyl cyclopentane cyclopentane we're going off the screen here and then finally this is tert-butyl or t-butyl cyclopentane now i said these are the common naming what are the systematic naming well in the systematic this is still butyl little pentane so let me write this down systematic systematic this is still butyl cyclopentane which makes sense this is this is very clearly a set of cyclopentane this is very clearly a butyl group but the systematic naming what we try to do is we try to name we try to name this group right here just as we would name a traditional chain but we ended with an ill so if you look at this right here what we do is we just consider the chain where we attach so if you look at we attached over here so the longest chain that it from that point is there and there so if you look at it like that it looks like you have one two three carbons and you have one carbon attached on the beginning so this little group right here in the systematic naming this looks like a 1 2 3 3 carbons that's the probe prefix so we're dealing with a probe and it's all going to be one group so it's a propyl group this is a propyl group but it has a methyl remember meth is one carbon it has a methyl group attached on the first carbon so this is one one methyl one methyl propyl now that describes just the group that describes one methyl propyl describes just this part right here that describes just that right over there and then to have the whole compound to describe the whole compound you'd put this in parenthesis so this is the systematic naming so one methyl 1/2 put an L there we've been in the same color one methyl because you have the your starting where you're attaching so one methyl you have a methyl group right there on that first car but it's appropriate change one two three propyl and then you would say cyclopentane cyclone that's the systematic name for that now if you look at this one right here what in the common name is isobutyl what you do is you look at where we attach where we attach is one two three carbons so once again I'm doing that same one two three carbons so once again this is a propyl probe is four three but with a methyl group now is attached to the one to the second carbon so this is two methyl let me make some space here this is two methyl so that describes this group right here that describes this entire group cyclopentane cyclopentane remember this is a systematic name you might sometimes see this referred to as isobutyl cyclopentane or two methyl propyl cyclopentane this is actually why l spelled it wrong and then finally do the same exact idea here but it becomes a little bit more interesting over here we are attached to this carbon and the longest chain I can do starting with that carbon it's just one is just one chain right there so we just have a two carbon chain right one two the prefix for two carbon is F ill or F F then since it's a group at fill and then we have two methyl groups we have two we have two methyl groups attached right over there and it's attached on the one carbon right this is one and this is two we call the one carbon where we are attached to the broader chain so this is going to be you would actually write one comma one to show that we have two groups attached to the first carbon and both of them are methyl and so we write one one dimethyl die for to die methyl so this entire group right here which we also called t-butyl when systematic naming is one one we have two groups attached to this first carbon one one dimethyl ethyl that's this whole thing this is the ethyl and then we have two methyls attached there that's why you write one one they're both attached to the one we have two of them that's why we wrote died over there so it's one one dimethyl ethyl and then finally cyclopentane cyclopentane so hopefully that doesn't confuse you too much I think if you watch the video over and over and try to practice it with your own problems the systematic name way is actually pretty pretty logical and actually if you have more than five or six carbons in the group they always or they tend to always use the systematic naming