Now the adduct represents the product of a Lewis based acid reaction. Here in this example we have two reactants combining together to give us one product. We are taking those two reactants and adding them together. That's why we say adduct, we're adding them together. The first structure in blue here, it's called acetone. It is reacting with boron trichloride and together they add to create this adduct.
Yeah, Now remember that we set a Lewis acid is an electron pair receptor. We said that this can be represented by H+ positive metals or where the center element has less than 8 electrons around it. If we look at boron boron's and group 3A. So it has three valence electrons and it picks up three more by forming bonds with these chlorines. But in total it only has six valence electrons around it, which opens up the possibility of accepting 1 electron pair in order to fill the octet rule.
So here we're going to say that this represents the Lewis asset and if that's Lewis acid, then acetone represents the Lewis base, it is the electron pair donor and what it's donating is this lone pair. Now this is a bit different from Bronsted-lowry acid definitions because in Bronsted-lowry acid definitions, the acid donates in H+. It kind of just gives away the H+ and stays behind. Here, if you're donating your electron pair, you're coming along for the ride because you're electrons are a part of your core as an element.
So here, this oxygen is going to share this lone pair with the boron to help make this bond. Remember, a bond itself is just two electrons and look how the whole structure came along with it. So we're adding together the Lewis acid and the Lewis base to give us our adduct. Now this is important. All Bronsted-lowry acids and bases are also Lewis acids and bases, and that's because Lewis is the broadest of the three types of acids and bases. It encompasses all types of acids and bases.
Bronsted-lowry is a little bit more narrowed, focused and then Arrhenius even more so we're going to say. However, many Lewis acids and bases are not classified as acids or bases Under Bronsted-lowry or Arrhenius models This here is a Lewis acid, but under Bronsted-lowry and Arrhenius it wouldn't be an acid because of the lack of an H+ ion. So as you can see, Lewis definition really expands as far out as it can in terms of collecting as many different compounds under the acid and base banners.
All right, so just keep this in mind. Lewis is the most broad, followed by Bronsted-lowry, and then Arrhenius seems to be the most narrow in its description of what classifieds an acid, What classifieds a base.