Intermolecular forces of an attraction between polar molecules of organic compounds in which hydrogen of one molecule is connected to the electronegative atom of O or N type of another molecule with the formation of hydrogen bond are reviewed in the course of “Organic chemistry”. Hydrogen bonds between molecules in alcohols lead to the higher temperatures of boiling in them, comparing to the corresponding halogen derivatives. Similarly, existence of dimers in solutions of carbonic acids defines exclusively high temperatures of their boiling (Fig. 4).