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

Wan-Sin Loh; Hoong-Kun Fun; R Venkat Ragavan; V Vijayakumar; M Venkatesh

doi:10.1107/S1600536811001589

. 2011 Jan 15;67(Pt 2):o403–o404. doi: 10.1107/S1600536811001589

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

Wan-Sin Loh ^a,^‡, Hoong-Kun Fun ^a,^*,^§, R Venkat Ragavan ^b, V Vijayakumar ^b, M Venkatesh ^b

PMCID: PMC3051742 PMID: 21523076

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.

Related literature

For background to pyrazole derivatives and their microbial activity, see: Ragavan et al. (2009 ▶, 2010 ▶). For bond-length data, see: Allen et al. (1987 ▶). For related structures, see: Loh et al. (2010 ▶, 2010a ▶,b ▶, 2011 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 ▶).

Experimental

Crystal data

C₁₁H₁₂N₂O
M _r = 188.23
Monoclinic,
a = 11.0898 (3) Å
b = 13.2171 (4) Å
c = 15.0265 (5) Å
β = 114.539 (2)°
V = 2003.58 (11) Å³
Z = 8
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 100 K
0.60 × 0.16 × 0.13 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ▶) T _min = 0.953, T _max = 0.989
22130 measured reflections
5845 independent reflections
3654 reflections with I > 2σ(I)
R _int = 0.063

Refinement

R[F ² > 2σ(F ²)] = 0.065
wR(F ²) = 0.166
S = 1.05
5845 reflections
284 parameters
2 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.38 e Å⁻³
Δρ_min = −0.30 e Å⁻³

Data collection: APEX2 (Bruker, 2009 ▶); cell refinement: SAINT (Bruker, 2009 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811001589/is2655sup1.cif

e-67-0o403-sup1.cif^{(24KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811001589/is2655Isup2.hkl

e-67-0o403-Isup2.hkl^{(286.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

Cg1 and Cg2 are the centroids of the C4B–C9B and C4A–C9A rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1B—H1NB⋯O1A	1.00 (2)	1.73 (2)	2.700 (2)	161 (2)
N2B—H2NB⋯O1Bⁱ	1.02 (2)	1.72 (2)	2.738 (2)	176 (2)
N2A—H2NA⋯O1Aⁱⁱ	0.98 (3)	1.74 (3)	2.704 (2)	171 (2)
N1A—H1NA⋯O1Bⁱⁱⁱ	0.98 (3)	1.74 (3)	2.691 (2)	162 (2)
C8A—H8AA⋯O1A^iv	0.93	2.47	3.370 (3)	163
C10A—H10C⋯Cg1ⁱⁱⁱ	0.97	2.61	3.464 (2)	147
C10B—H10E⋯Cg2	0.97	2.71	3.524 (3)	142

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) .

Acknowledgments

HKF and WSL thank Universiti Sains Malaysia (USM) for the Research University Grant (1001/PFIZIK/811160). WSL also thanks the Malaysian Government and USM for the award of a Research Fellowship. VV is grateful to the DST–India for funding through the Young Scientist Scheme (Fast Track Proposal).

supplementary crystallographic information

Comment

Antibacterial and antifungal activities of the azoles are most widely studied and some of them are in clinical practice as anti-microbial agents. However, the azole-resistant strains had led to the development of new anti-microbial compounds. In particular, pyrazole derivatives are extensively studied and used as anti-microbial agents. Pyrazole is an important class of heterocyclic compounds and many pyrazole derivatives are reported to have the broad spectrum of biological properties such as anti-inflammatory, antifungal, herbicidal, anti-tumour, cytotoxic, molecular modelling and antiviral activities. Pyrazole derivatives also act as anti-angiogenic agents, A3 adenosine receptor antagonists, neuropeptide YY5 receptor antagonists as well as kinase inhibitor for treatment of type 2 diabetes, hyperlipidemia, obesity and thrombopiotinmimetics. Recently urea derivatives of pyrazoles have been reported as potent inhibitors of p38 kinase. Since the high electronegativity of halogens (particularly chlorine and fluorine) in the aromatic part of the drug molecules play an important role in enhancing their biological activity, we are interested to have 4-fluoro or 4-chloro substitution in the aryls of 1,5-diaryl pyrazoles. As part of our on-going research aiming the synthesis of new anti-microbial compounds, we have reported the synthesis of novel pyrazole derivatives and their microbial activities (Ragavan et al., 2009, 2010).

The title compound (Fig. 1), consists of two crystallographically independent molecules, with similar geometries and exist in keto-form with the bond length of C═O being 1.286 (2) Å in molecule A and 1.283 (2) Å in molecule B. This indicates that the compound undergoes an enol-to-keto tautomerism during the crystallization process In molecule A, the pyrazole ring (N1A/N2A/C1A–C3A) is approximately planar [maximum deviation of 0.0262 (16) Å at N2A] and forms a dihedral angle of 43.28 (12)° with the attached phenyl ring (C4A–C9A). In molecule B, the pyrazole ring (N1B/N2B/C1B–C3B) is approximately planar with a maximum deviation of 0.0209 (15) Å at N1B and form a dihedral angle of 46.88 (11)° with the attached phenyl ring (C4B–C9B). The ethyl unit (C10B/C11B) in the molecule B is observed to be disordered over two positions with a site-occupancy ratio of 0.508 (5):0.492 (5). Bond lengths (Allen et al., 1987) and angles are within the normal ranges and are comparable to the related structures (Loh et al., 2010, 2011; Loh et al., 2010a,b).

In the crystal packing (Fig. 2), intermolecular N2A—H2NA···O1A and N2B—H2NB···O1B hydrogen bonds (Table 1) link the neighbouring molecules to form dimers, generating R₂²(8) ring motifs (Bernstein et al., 1995) and are further packed into three-dimensional network by intermolecular N1B—H1NB···O1A, N1A—H1NA···O1B and C8A—H8AA···O1A hydrogen bonds (Table 1). The crystal structure is further stabilized by C—H···π interactions (Table 1) involving Cg1 (C4B–C9B) and Cg2 (C4A–C9A).

Experimental

The compound has been synthesized using the method available in the literature (Ragavan et al., 2010) and recrystallized using the ethanol-chloroform 1:1 mixture (yield 81%, m. p. 361.3–362.1 K).