Usporedba vrelišta alkana može biti dobar povod da se učenici upoznaju sa zasadama organske, primijenjene i teorijske kemije, od problema ukapljivanja prirodnog plina do pojmova poput strukturne izomerije, homolognog niza, pa i s teorijom grafova u kemiji. Stoga pitanje vrelišta alkana može biti dobra tema za problemski pristup nastavi kemije u našim srednjim školama.The fact that the boiling point of alkanes rises with the number of carbon atoms and drops with their branching has many consequences. The first is the difference in the use of two kinds of natural gas, methane and butane. The second is the problem of properties inside the homologous series that from the one hand connects the boiling points of alkanes with the properties in other homologous series, and from the other gives the teacher an opportunity to inform the students about the chemical graph theory, i.e. the Wiener number (the first topological index) which has been developed for solving this particular problem. In this contribution, the basics of the chemical graph theory are presented, and also pointed out are the properties in the homologous series which inspired 19th century chemists to propose the periodic system of the elements. At any rate, the problem of the boiling points of alkanes is a valuable topic in the problematic teaching of chemistry
