Search

Abstract: This Letter reports the evidences for intramolecular six-membered N–H···O hydrogen bonding in N-benzyl benzamides and five-membered N–H···N hydrogen bonding in N-(pyridin-2-ylmethyl) benzamide. Intramolecular six-membered N–H···X (X=O or F) hydrogen bonding in 2-methoxyl- or 2-fluorobenzamides is used to lock the amide proton from forming strong intermolecular N–H···On bonding. As a result, for the first time the new intramolecular hydrogen bonding patterns are observed in the crystal structures of nine amides, whereas the whole molecules give rise to a new class of three-center hydrogen bonding motif. 1H NMR study in chloroform-d also supports that this weak intramolecular hydrogen bonding pattern exists in solution. [Copyright &y& Elsevier]

Abstract: The capacity of sulfur to form intramolecular five- or six-membered S⋯H–N hydrogen bonding in aromatic amides is assessed. The five-membered S⋯H–N hydrogen bonding is observed in crystal structures of five compounds, whereas the six-membered S⋯H–N hydrogen bonding is revealed in crystal structures of three compounds. The trityl group has been used to promote formation of the weak hydrogen bonding because it efficiently inhibits the competition of the intermolecular CH–N hydrogen bonding. (2D) 1H NMR experiments indicate that both patterns also exist in chloroform. [Copyright &y& Elsevier]