Non-hydrogen-Bonding Intramolecular Interactions: Important but Often Overlooked

Our focus in this chapter is upon intramolecular noncovalent interactions, electrostatically driven, but not including hydrogen bonding. They often involve a positive σ-hole or π-hole on a covalently-bonded Group IV – VII atom, in conjunction with a negative site in the molecule. Examples are given involving NO2 groups, Si–O–N bond angles, and specific 1,3-Si—O, 1,4-S—O, 1,4-Se—O, 1,3-P—Cl and 1,4-C—O interactions. These examples demonstrate that intramolecular interactions can play significant roles in determining the structure of a molecule and also its reactive properties. This often involves stabilizing a particular conformation, but can also include markedly affecting bond lengths and/or angles. It is essential to take intramolecular interactions into account in trying to understand and predict molecular behavior, and furthermore to exploit them in designing new materials, in pharmacology, crystal engineering, etc.