Giant ring compounds

Just as amino acids are the starting points for the proteins, so another group of giant molecules, the nucleic acids, find their building blocks in substances derived from two simple related ring compounds, purine and pyrimidine. 

An X-ray crystal structure of the 18-membered ring compound, 63 [24], shows that it adopts a giant chair conformation not unlike that of cyclohexane, albeit slightly less puckered, with essentially linear diynes and internal angles of 115.5° at the comers. Unlike the permethylated derivatives of exploded pericyclynes, crystals of the perspirocyclopropanated derivative, 63, explode when struck [33]. 

Compound 45 is nonplanar, based on molecular model calculations, due to the presence of five-membered rings, and therefore offers the possibility to create bowl-shaped molecules via flash vacuum pyrolysis (FVP) [86, 89]. The C150 disc 47 is the largest disc with threefold symmetry yet made [86], whereas the giant nanographene 48 with its 222 carbon atoms is the largest PAH to be synthesized and characterized to date [88]. 

Although the structural chemistry of molybdenum and vanadium phosphates is very diverse these compounds seem to be prototypes for open framework transition and main group metal phosphates. Recent results have shown that zeolite-like compounds like zinc/cobalt phosphates [731, indium phosphates [74], nickel/aluminum phosphates [75], cobalt/boron phosphates [76], manganese and cobalt phosphonates with giant 44-membered rings forming ellipsoidal cavities [77] can be synthesized. All these examples show that the diverse chemistry of octahedral-tetrahedral framework structures is a vast field where... 

While the phase was also found in ni-tro compounds with two benzene rings [28], re-entrant phenomena in liquid crystals made a giant leapforward in 1979, when the stable Nj-e-SmA transition [29] and multiple re-entrance [30] was discovered at 1 atm... 

---