 So let's look at some alcohols for example. This if you'll count has two carbons attached to it and so our prefix for two is F and you see we have a single bond between the carbons and so that means that it would be an A in for the alkanes that have all single bonds and then you see our OH group which makes it an alcohol. So this is F and all, E-T-H-A-N-O-L. So it's a carbon with a hydroxyl group attached and then that carbons attached to another carbon that has four or three hydrogens. Let's look at propanol and so pro tells us that we have three carbons one, two, three, so there are our three carbons and then here is our OH group or our hydroxyl group. So this is propanol, a probe for three carbons, propanol. But let's look at an isomer of propanol and that will be isopropanol and with isopropanol you can see that the middle carbon is the one that has the hydroxyl group attached to it. So here's carbon, carbon, carbon and then the hydroxyl group attached in the middle. So propanol and isopropanol are isomers of one another. They both have the same molecular formula that you can see that they're structural formula and it's very different.