Naming two isobutyl groups systematically
About this video
The video converts a common name for a branched alkyl group into its systematic IUPAC name. You find the longest carbon chain starting from the point where the group attaches to the main backbone, then name the branch as a substituent with its position, so isobutyl becomes 2-methylpropyl. When the same substituent appears twice, the prefix changes from di- to bis- for complex groups, and the parent ring is then named.
You'll be able to
- find the longest chain from the attachment point of a branched group
- convert a common name such as isobutyl into a systematic name such as 2-methylpropyl
- explain why bis- replaces di- for complex substituent names
Key words
- Systematic name
- A name built by rules from chain length, position numbers and substituent names, as opposed to a traditional common name.
- Substituent
- A group attached to the main chain or ring of a molecule, such as a methyl or propyl group.
- Propyl group
- A three-carbon chain attached at one end, numbered 1, 2 and 3 from the attachment point.
- Methyl group
- A single carbon branch, named as a substituent on a chain.
- Bis-
- A multiplying prefix used instead of di- when the substituent name itself contains numbers or parentheses.
Transcript
- [Instructor] In the last video, we named this molecule using the common names for this group right over here and I thought it would be fun to also use- to do the same thing but use the systematic name. So in the last video, we called this isobutyl but if wanted to do it systematically, we would look at this group, we would start at where it is attached to the main backbone, and we would think about the longest chain of carbons from there.
So if we start there, we can get one, two, three carbons. So if we're dealing with three carbons, then this is going to be a propyl group, and we would number it one, two, three. And we see on the two carbon of the propyl group, the two carbon of the propyl group, we have a one carbon group right over here, so this is a methyl group branching off the two carbon of the propyl group.
So we could call this, we could call this thing the systematic name, instead of calling it isobutyl, we could call it two methyl, that's the methyl group right over there. So let me write this down, two, two methyl propyl, two methyl propyl, two methyl propyl.
And so this is the systematic name, and of course there is two of them. This is a two methyl propyl right over here instead of an isobutyl, we'll call it two methyl propyl. And this is another two methyl propyl. So instead of writing, instead of writing the five, seven diisobutyl here, we can instead substitute that with the systematic names.
So let's do that. Let me copy and paste everything else that comes before it. So let me copy, copy and paste it. Whoops. Whoops, I'm in the wrong layer of my program. Let me go one layer down. So let me copy and paste it again. Copy and paste, there we go. So I got that part.
But now I'm going to write this part differently. So we still have stuff, we still- it's still on the five carbon and the seven carbon of our main chain. So five comma seven, and we have two of'em, but when we're using systematic naming, we won't say di- this thing, instead we say bis-.
So five comma seven bis, that says, "Hey, we've got two of what I'm about to say." Bis- this thing. So let me copy, dude, that's in a different layer. Let me copy and let me paste that. Bis- this stuff right over here, and then, of course, we have cyclooctane.
And then, of course, we have cyclooctane, and we are done. We have named it systematically as well.
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