Revisiting these super important molecules after a break has been a good thing. I am now aligned with the structural numbering of the hex-a-penta double ring. I can more easily visualize the 6 + 5 - 2 = 9 double ring and the 4N + 5C = 9 ring atoms. It is so much easier to use numbering to get around the backbone and to look at the "Will I bond?" or "Will I have stay at home electrons?" nature of these molecules. I like being able to visualize the structural rigidity of these molecules and the nature of the hydrogen bonding. Enjoy. MP4 recording     MP3 recording -- -- Your browser does not support the audio element.