The following text is from Solomons, Fryhle and Snyder Organic Chemistry Third Edition, chapter 1 "The Basics: Bonding and Molecular Structure", page 13, topic 1.5 "Resonance Theory", sub topic 1.5B "Schematic Energy Level Diagrams of Some Mesomeric Molecules/Ions":
Energy level diagrams of some resonating structures are given as follows. (Note: The downward arrow marks the conventional mesomeric energies and indicates energy level).
It is given that the downward arrows in examples 1, 2, 3, and 4 mark the conventional mesomeric energies. What is meant by "conventional mesomeric energy"? I searched for this word on Google as well as on this site, but I couldn't find any relevant information.
What is the purpose of the downward arrows in the above energy level diagrams? Is that to depict the structure with least energy or the one which is the most stable? I thought this was the reason until I saw example 5. The arrow goes from the structure which has the highest stability to the one which has the least stability. Is there any specific reason for this upward arrow or is it just a misprint? I was unable to see any other energy level diagrams with these arrows, so is this an outdated convention followed by the book?