Everyone, in this video, we're going to take a look at disubstitutive benzenes, which are compounds where benzene is the parent chain, and it has two substituents. Now these substituents are numbered in alphabetical order. So if we have, for example, Fluorine and Bromine, bromo comes before fluoro, so we'd start numbering at the bromo position. Now here, this would tell us in terms of the naming convention, we'd say the location of each substituent, and at the end of the name, we'd say Benzene.
Benzene itself is pretty unique because we could number where these two substituents are numerically as 1,2, 1,3, or 1,4, or we could do a brand-new way of designating their locations in the form of ortho, meta, and para. Here in this example, these are all dichlorobenzenes. The chlorines are in different locations. Now here, they're in positions 1,2 in this first image. Here when they're in the positions 1,2, we say 1,2-dichloro or we could say ortho-dichloro. In the next one, they are 1,3 to each other, so instead of saying 1,3-dichloro, we could say meta-dichloro. And then finally, there are positions 1,4 here, so we have 1,4-dichlorobenzene, or we could say para-dichlorobenzene.
Now, the two substituents don't have to be the same, they could be the same or they can be different from each other. This ortho, meta, and para convention still would work. Now our memory tool here to help us remember the order is "order more pizza." Now I know in college, a lot of us kinda survive on pizza, at least that's the way it was for me when I was in college. So "order more pizza" gives us the letter designation of 1,2, 1,3, and 1,4. Order 1,2, ortho, more, 1,3, meta, and pizza, 1,4, para. Alright? So keep that in mind. We can name these two substituents by our traditional numerical method, or we could do ortho, meta, and para.