With the increase of the length of the conjugated chain, delocalization of p-electrons increases, coupling energy and thermodynamic stability of compounds increases. Considering open conjugated systems in the subsequent courses like: “Bioorganic chemistry”, “Biochemistry”, “Chemistry of natural compounds”, “Chemistry and technology of natural heterocyclic compounds” (Traven, 2004) such a data obtained by the students, is a starting point for an explanation of higher thermodynamic stability of polyenes, such as ß-carotene (pro-vitamin A), widespread in the nature in comparison with the polyenes with the isolated double bonds (Fig. 1).