Attractive Intramolecular Edge-to-Face Aromatic Interactions in Flexible Organic Molecules

Recent X-ray crystallographic and NMR evidence indicates that relatively weak intramolecular edge-to-face interactions between aromatic rings can affect or determine the conformation of organic molecules in the solid state and in solution. Experimental estimates indicate that these interactions are energetically attractive by ca. 1.5 kcal mol-1 but disfavored in solution by entropic factors due to the restricted internal mobility. Hence, these interactions are more manifest at low temperature in solution or in crystal structures where conformational entropy effects are negligible.