00:01
Hi there.
00:02
We need to determine if these are correct or incorrect, and if they're incorrect, we need to choose the correct name.
00:08
So the best way to do that is to sketch out what is described here and see if the name is correct.
00:15
So we have one three dimethyl pentane.
00:19
So pentane means five carbons, single bonded.
00:24
And on the first carbon, there's a methyl group.
00:28
And on the third carbon, there's a methyl group.
00:34
Oops, i left off a carbon there.
00:36
Okay, so we have our pentane.
00:37
We have a methyl off the first carbon, a methyl off the third carbon.
00:42
All right, so this is incorrect.
00:47
Remember, all of those other bonds are to hydrogens, but i am not going to show those.
00:53
Okay, so this is incorrectly named because now that we've sketched this out, we see that the longest continuous chain is right here.
01:07
We will never have a substituent group coming off the first carbon, at least an alkane group, because that just makes the chain longer.
01:15
We could have other things like bromines and things like that, but we're not going to have an alkan coming off of the first carbon.
01:23
So what we have here is a hexane because the longest carbon is six.
01:31
And now if we number these carbons from the end to give the branch its lowest possible number, we see that that branch is a one carbon chain coming off the third carbon.
01:46
So this will be three methyl hexane.
01:53
So the correct name for this is three methyl hexane.
01:59
Okay, let's move on to letter b.
02:01
Letter b describes something that they're calling two -ethyl propane.
02:06
All right, well, propane means a three -carbon chain.
02:12
And 2 -efl gives us a 2 -carbon chain.
02:16
Let me go down with that.
02:18
It gives us a 2 -carbon chain coming off of that.
02:22
So we see that our longest continuous chain here is actually a 4 -carbon chain.
02:29
This is going to be a butane.
02:31
So this one is incorrect.
02:38
And as i mentioned a moment ago, it's going to be a butane because the longest chain has 4 carbons.
02:45
And coming off of the second carbon because we want to start counting from the end where it will be closest.
02:52
So coming off of the second carbon, we have a methyl group.
02:56
So this is two methyl butane...