Thank you. Hello and welcome to this video on naming and drawing branch chain alcohols. You'll remember from National 5 that you're able to name straight chain alcohols where the hydroxyl group could be on any of the carbons within the chain. In higher we're going to extend that to now have a look at branch chain alcohols. So the rules for naming the branch chain alcohols are very similar to those that you've used for naming branch chain alkanes and alkenes.
Step one is always to find the longest chain that contains your functional group in this case that is the the OH hydroxyl group. So our longest chain is this one here with four carbons. So if you were to name that then you would call that the butane part.
The second step is to number the chain from the end closest to the hydroxyl. So we're going to have one, two, three, four. So if we didn't have this branch here this would be butane 2-ol.
So we're going to just write that out underneath. So we've got butane, I'm just going to put the number in blue to match up. Okay, so remember we use dashes between letters and numbers. So we've got butan dash 2 dash all. We're going to name the branches and number them according to the numbering that you've already carried out.
So you don't re-number for the branches. So our branch here, all we have is this one little branch with a single carbon. So that would be a methyl group. Okay, and our methyl group is also on carbon 2. So we're going to have 2-methylbutan2ol. If you had more than one branch, then you would need to use di or tri if they were the same type of branch.
For example, if we had another methyl. ethyl here, that would be dimethyl. But if the branches are different, for example if we had an ethyl group, you would name them alphabetically, so ethyl before methyl. And that is ignoring any prefix that you have on the front, so any dies or tris. So I'm going to show you some other examples.
I have the rules written down the side here, you could pause the video now, have a try answering these yourselves and then play again to see what the answers are. Let's have a look at our first example. Here we need to find our longest chain. There's a lot of different chains.
You've got one going through the middle here, one going across here, another one here and then you have another one going along here. If you count up all of them you'll find each of them contains six carbons. So in fact we can just choose the middle chain here for ease. So that is our longest chain. So if we were just to name that by itself it would be hexane.
So we're just going to stop at the hexane. Step number Number 2, we need to number our chain, so we've got 1, 2, 3, 4, 5, 6. Numbering from the right because that gives the OH the smallest number. So that means that we have hexan 3 all.
Now we need to have a look at the branches. You'll notice that we have two branches here. So we've got this branch up at the top, which has two carbons, so it's based on ethane.
So this is an ethyl group. And we've got this one here on the second carbon, which has got one carbon so that's based on methane and is a methyl group. We need to name these so that we have them alphabetically within the name. So that means that we're going with the ethyl even though it's on the higher numbered carbon.
So we're going to have 4 dash Ethyl, another dash because we're going to put in another number. Our next number is 2 for the methyl. 2 dash methyl. So we've got 4 ethyl, 2 methyl, hexan, 3 all. Let's have a look at our next example.
So here is our second example. Again, we need to find the longest chain. So the longest chain here is again the one going through the middle.
And we're going to number it so that the OH gets the smallest number possible. So you can go from either end. We're going to start from the left this time. 1, 2, 3, 4, 5. So because we've got 5 carbons, it's going to be based on pentane.
And our OH group is on the third carbon. So we've got pentane 3, all. Now we need to have a look at our branch.
We've only got one single branch on this one here. So we've got this part here, which is a methyl. Methyl is on number 3. So our full name will be 3-methyl-3-methyl-3-methyl-3-methyl-3-methyl-3-methyl-3-methyl-3-methyl-3-methyl-3-methyl- pentane 3ol.
So that's how we name the molecules that you're given as diagrams. Now we're going to have a look at changing from the name into the structure. Just like we would have with branched chain alkanes, we're going to work from the end of the structure forwards. So here at the end of the structure we've got pentane. So that tells us we must have five carbons in a row.
So we're just going to draw out those five carbons. For your numbering, you've got a 1 here. So that's telling you on the first carbon, you must have your OH group.
So I'm just going to put it at this end. So here's our first carbon. In terms of numbers, it's also telling you on carbons 2 and 3. you have a methyl group. So we've got two methyls.
So if this is carbon 1, this will be carbon 2 here. So we're going to have a methyl group here. This is carbon 3, so we'll have another methyl group here.
I'm just going to go ahead and fill in the rest of the hydrogens. So remember each carbon needs to have four bonds coming out of it. So draw in the structure and then go round and fill in the rest at the end.
So here you have 2, 3 dimethyl pentan 1-ol. Having a look at our next example, we have 4-ethyl 2-methyl hexan 3-ol. So starting from the end of the name, we've got hexan, which tells us we must have 6 carbons. Okay, so there are our six carbons.
On the third carbon, which we're going to take as being this one here, we have an OH group. On the second carbon, you have a methyl. And on the fourth carbon, you have an ethyl group. So if this is the third carbon, this one is our second. So there is our methyl group and then on the fourth carbon we have an ethyl group.
So CH2, CH3. And then just go round and fill in the rest of the hydrogens, making sure that everything has four bonds. So that was just a really quick tutorial on how to name and draw branched chain alcohol molecules. I hope that you enjoyed this video.
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