 This is a qualitative investigation and hopefully it's one that you're already familiar with. So we can just very quickly look at how it is that we can conduct an investigation to test for the presence of the carbon-carbon double bond in organic molecules. So I hope that what you've been thinking as you've looked at the beginning of this video is, well, the carbon-carbon double bond can actually be identified very easily with the addition of bromine water. Bromine water is a great test substance for unsaturated hydrocarbons. So I'll put that under there for unsaturated hydrocarbons because what will happen with these unsaturated hydrocarbons is they will undergo an addition reaction. Structurally, if we have say for example let's call it pent one in four five one two three There we go. So here's our double bond here and what we're going to be doing is we're going to add bromine water. Now there are a couple of variations on this and it's going to be interesting to see just how how many different options you're going to be expected to understand. But I would assume that one of the simple things that you can do with this is to just look at the way that the bromine is going to add across the double bond. So we've got a bromine on the first carbon and a bromine on the second carbon and then three four five carbons and of course all our hydrogens around and I haven't added all of those in and of course you can certainly do that. And I'm hoping by now that you'll you'll have been understanding that really what we do with our organic compounds is we put in our functional groups, we put in our number of carbons, make sure we locate our functional groups and then we fill up all of our carbons with four bonds in total and anything that isn't already part of the functional groups that we've labeled we just add hydrogens in there. So you can see this is pent one in and with the addition of bromine water in aqueous, it becomes one, two, di-bromo pentane. Now it is possible that we can look at the way that the bromine combines in water. You may see some variations on this where the bromine water actually forms a little complex where the bromine is actually bonded to a hydroxyl group and they can actually add across that double bond as well. And there are occasions where we have seen that that is a variation on this theme. I think it's probably important to have a bit of a chat and class about it and just focus on this more simple version of the addition reaction with bromine water.