Intramolecular Six-Membered and Three-Center C−H···O Hydrogen Bonding in 1,4-Diphenyl-1,2,3-Triazoles

This paper reports the first example of the intramolecular three-center C−H···O hydrogen bonding. Nine 1,4-di(2-methoxy and/or i-butoxy)phenyl-1,2,3-triazole derivatives, that is, 1−9, are prepared. The X-ray diffraction studies reveal that 1, 2, and 4, which bear a methoxyl or i-butoxyl group on the N-1- or C-4-substituted benzene ring, form a six-membered C−H···O hydrogen bond between the C5−H of their triazole unit and the alkoxyl O, while 5−8, which bear two methoxyl and/or i-butoxyl groups on the similar benzene rings, form two three-center C−H···O hydrogen bonds. It is also found that in most cases the hydrogen bond on the C-4 side is shorter than that on the N-1 side and both of them can be stabilized by the aromatic stacking and other intermolecular interactions. The (NOESY) 1H NMR experiments in CDCl3 and CDCl3-DMSO-d6 mixture (4:1) support that both the six-membered and the three-center C−H···O hydrogen bonds also exist in solution.