5-Ethyl-4-phenyl-1H-pyrazol-3(2H)-one

Abstract

The asymmetric unit of the title compound, C11H12N2O, consists of two crystallographically independent mol­ecules (A and B) with similar geometries. Both mol­ecules exist in a keto form, the C=O bond length being 1.286 (2) Å in A and 1.283 (2) Å in B. The dihedral angles between the pyrazole ring and the attached phenyl ring are 43.28 (12) and 46.88 (11)°, respectively, for A and B. The ethyl unit in mol­ecule B is disordered over two positions with a site-occupancy ratio of 0.508 (5):0.492 (5). In the crystal, each of the independent mol­ecules forms a centrosymmetric dimer with an R 2 2(8) ring motif through a pair of N—H⋯O hydrogen bonds. These dimers are further connected into a three-dimensional network by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds. Inter­molecular C—H⋯π inter­actions are also present.

AMHB: (Anti)aromaticity-Modulated Hydrogen Bonding

“…A survey of the online Cambridge Structural Database (WebCSD), in which H-bond-donor/-acceptor distances were compared, found that the average distance for 2a in five crystals of its derivatives − is 0.147 Å shorter (2.703(2) vs 2.850(4) Å, see Figure a) than for 2a ′ in 12 crystal structures. − Conversely, the average N···N distance in 3a derivatives in three crystal structures − is 0.110 Å longer (3.013(3) vs 2.903(3), see Figure b) than 3a ′ derivatives in five crystal structures. − These observations offer strong experimental support for the notion of aromaticity assisted H-bonding and aromaticity disrupted H-bonding in the cases of 2a and 3a , respectively.…”