Question 3F.13

[ATingin_3I]

I have a question about question 3F.13. The question asks which arrangement of molecules would produce the strongest intermolecular attractions. Since dichloromethane has an overall dipole and contains hydrogens, it is capable of forming hydrogen bonds, which would be the predominant intermolecular interactions present. In this case, the chlorine atoms would have a partial negative charge, and the hydrogen atoms would have a partial positive charge. Therefore, hydrogen bonds would form between the hydrogens of one molecule and the chlorines of adjacent molecules. Arrangement I is clearly not the correct answer, since molecules are haphazardly arranged, with chlorines facing other chorines, and hydrogens facing other hydrogens, causing electrostatic repulsion. However, I don't understand why choice 2 is any more correct than choice 3. In both cases, the hydrogens of one molecule are on a plane perpendicular to the chlorines on the molecule next to it. This means each hydrogen atom on one molecule can form hydrogen bonds with both chlorines on the adjacent molecule. This means there are four hydrogen bonds between any two molecules. This is true in both arrangement II and arrangement III. What exactly makes the interactions in arrangement II stronger?

[Brooke Yasuda 2J]

In choice III, while it is true that there are favorable attractions resulting from the chlorine atoms being close to the Hydrogen atoms. However, in this orientation there are also Chlorine atoms that are facing each other, and this will cause repulsions that are not favorable. In contrast, choice II has the positive dipoles and negative dipoles facing one another, creating favorable attractions. In this case there are not immediate, noticeable repulsions between any atoms