An oximino tautomer of 1-n-decyl-4-hydroxy­imino-3-methyl-1H-pyrazol-5(4H)-one

The title compound, C₁₄H₂₅N₃O₂, consists of a five-membered heterocyclic ring to which a pendant decyl group is attached. The oximino tautomeric character of the mol­ecule is clearly defined by the distribution of well defined double bonds in the heterocycle region (one C=O and two C=N). The most conspicuous packing inter­action is the strong inter­molecular hydrogen bond linking the oximino OH group and the carbonyl O atom to define broad planar hydro­philic strips running along the unique b axis. The alkyl chains adopt a fully extended conformation and lie almost at right angles to these one-dimensional structures, defining their hydro­phobic counterpart.

S1. Comment

Pyrazolones have attracted attention because they exhibit prototropic tautomerism (Elguero, 1996; Uraev et al., 2000; Gilchrist, 2001), and they have been extensively studied both in solution and in the crystalline phase (Chmutova et al., 2001).

To date, most pyrazolones described are 1-aryl-o-1-unsubstituted derivatives. Bartulin et al. (1992) showed that 3-methyl-5-pyrazolones can be easily alkylated at atom N1 with primary alkyl halides. Nitrosation of some 1-n-alkyl-3-methyl-5-pyrazolones was also reported (Bartulin et al., 1994). Four important tautomeric structures can be envisaged for nitrosopyrazolones (see first scheme below). On the basis of ¹⁵N NMR measurements for 1-ethyl-3-methyl-4-nitroso-5-pyrazolone, an equilibrium in solution between two nitroso structures, A and B, was suggested (Bartulin et al., 1994). This result should be valid for any 1-n-alkyl homologue since they exhibit similar patterns in their ¹H and ¹³C NMR spectra. This finding was rather unexpected, because nitrosopyrazolones usually exist as oximino tautomers (structure C), as do many other nitroso compounds (Wiley & Wiley, 1964; Ivanova & Enchev, 2001; Krzan et al., 2001 or 2000). Unfortunately, Bartulin et al. (1994) did not succeed in obtaining single crystals from the compounds they reported, and the question of what the actual situation would be in the solid state remained open.

On the other hand, Barjesteh et al. (1996) described the crystal structure of metal complexes obtained from 1-phenyl-3-methyl- and 1,3-dimethyl-4-hydroxyiminopyrazol-5-one, and they suggested the complexes as having an oximino structure; however, a closer analysis of the bond lengths seems to point towards a 4-nitroso complex in both cases. The structure of 4-[(N-benzoyloxycarbonylvalyl)]-3-methyl-5-pyrazolone has also been described (Bertolasi et al., 1978), but in this case the oximino structure is locked by the acyl group. Holzer & Hallak (2004) obtained a mixture of E and Z stereoisomers of the 4-hydroxyimino derivative by nitrosation of 1-phenyl-3-methyl-5-pyrazolone, although no crystal data were reported.

Following our interest in the subject and following on from the results reported by Bartulin et al. (1994), 1-n-decyl-3-methyl-5-pyrazolone was nitrosated in our laboratory and the product obtained analyzed by NMR and IR techniques.

Single-crystal X-ray structure analysis showed the product to be the title compound, (I), with a structure quite different from that observed in solution.

Fig. 1 is a labeled ellipsoid plot of the molecule of (I), showing the interactions with the neighbouring molecules. The molecule consists of a heterocycle to which a pendant decyl group is attached. Table 1 presents a survey of selected bond lengths and angles in the heterocycle. It is apparent that the C3═O1, C2═N3 and N1═C1 distances correspond to well defined double bonds, the latter being considerably shorter than the corresponding values in related compounds (Belmar et al., 2004). The C2═N3 distance and the presence of the H atom attached to O2 (clearly visible in the difference Fourier map) confirm that the crystal structure contains the anti-oximino tautomer, all distances in the structure being in full agreement with the corresponding values in similar systems reported in the literature (Talberg, 1975)

In the present case, the prototropic tautomerism favors, in the solid state, the formation of the anti conformer, allowing the formation of a broad one-dimensional network (hereafter `the strip') along the unique b axis, built up through a strong intermolecular hydrogen-bond between the oximino group in one molecule and the carbonyl group in a neighbouring molecule (Fig. 1 and Table 2).

The heterocyclic rings thus connected are almost coplanar to each other [the dihedral angle is 2.95 (1)°] and constitute a planar core to this strip [the maximum deviation from the mean plane is 0.07 (s.u.?) Å for atom O1]. The alkyl chains adopt a fully extended conformation and lie almost at right angles to the core, their axis subtending an angle of ca 10° to the plane normal, in an alternating `up and down' fashion, or, in other words, with neighboring chains in the same strip being trans to each other.

Strips stack in such a way as to have the corresponding cores parallel and at a distance of 3.12 (1) between mean planes (Fig. 2). Rings in closest contact are related by a centre of inversion and offset laterally so that the center-to-center approach, Cg···Cg(1 − x, 2 − y, 1 − z), is 4.23 (1) Å (Cg is the center of the heterocycle), with a slippage angle as large as 39.1 (1)°.

These planar strips located at x ~0.50 (Fig. 2) constitute the hydrophilic part of the structure; the alkyl chains, interdigitating parallel to each other at x ~0 and 1, define the hydrophobic counterpart. Each one of these aliphatic segments appears surrounded in an hexagonal fashion by another six, almost parallel, neighbouring segments displaying shortest-approach C···C distances in the range 4.30 (1)–5.16 (1) Å.

S2. Experimental

The title compound was obtained by nitrosation of 1-n-decyl-3-methyl-5-pyrazolone, following the procedure already described in the literature (Bartulin et al., 1994) (yield 63%; m.p. 360–361 K). NMR measurements agreed with previous findings of two nitrosopyazolone tautomers (A and B in diagram). IR spectra recorded using KBr pellets of crystals obtained by rapid evaporation of chloroform, acetone and ethanol solutions were very similar, although little information could be extracted. The spectra are characterized by a strong band at 1700 cm⁻¹ (C═O) and a medium band around 1595 cm⁻¹ (NO). The fact that the ratio of C═O to NO is not the same in all cases may be a consequence of different tautomer ratios. Single crystals were obtained by evaporation of an ethanol solution.

S3. Refinement

Those H atoms defined by the stereochemistry were placed at ideal positions (C_sp2—H = 0.97 Å and C_sp3—H = 0.96 Å) and allowed to ride. Methyl groups were allowed to rotate around their local threefold axis. The H atom attached to O2 was found in a difference Fourier map and refined with restraints [O—H = 0.86 (2) Å]. Isotropic displacement parameters for all H atoms were defined as U_iso(H)_iso = xU_eq(host), where x is 1.2 for non-methyl and hydroxy H atoms, and 1.5 for methyl H atoms. The pendant alkyl group appeares highly mobile, with rather large anisotropic displacement parameters which impaired the calculation of the C—C distances, particularly for the outermost C atoms. Full use was made of the CCDC package for searching the Cambridge Structural Database (CSD; Allen, 2002).

Computing details

Data collection: SMART-NT (Bruker, 2001); cell refinement: SAINT-NT (Bruker, 2000); data reduction: SAINT-NT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-NT (Bruker, 2000); software used to prepare material for publication: SHELXTL-NT.

Figures

	Fig. 1. : Ellipsoid plot showing the way in which the strips are formed. Only the reference molecule in the asymmetric unit has been drawn in full 40% thermal ellipsoids, symmetry related molecules being represented by open ellipsoids. H atoms not involved in hydrogen bonds have been omitted.
	Fig. 2. : Packing diagram showing the stacking of strips. Note the hydrophilic core at x ~0.50 and the hydrophobic counterpart atx\sim 1.0

1-n-decyl-4-hydroxyimino-3-methyl-1H-pyrazol-5(4H)-one

Crystal data

C14H25N3O2	F(000) = 584
Mr = 267.37	Dx = 1.114 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 17.948 (4) Å	Cell parameters from 3987 reflections
b = 8.2512 (17) Å	θ = 4.1–26.7°
c = 10.762 (2) Å	µ = 0.08 mm^−1
β = 90.461 (4)°	T = 295 K
V = 1593.7 (6) Å^3	Prisms, yellow
Z = 4	0.22 × 0.18 × 0.14 mm

Data collection

Bruker SMART CCD area-detector diffractometer	1831 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.059
Graphite monochromator	θmax = 28.0°, θmin = 2.3°
ϕ and ω scans	h = −22→22
11384 measured reflections	k = −10→10
3600 independent reflections	l = −13→14

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.065	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.184	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0861P)^2] where P = (Fo^2 + 2Fc^2)/3
3600 reflections	(Δ/σ)max < 0.001
177 parameters	Δρmax = 0.16 e Å^−3
2 restraints	Δρmin = −0.10 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.38804 (12)	1.2382 (2)	0.50685 (19)	0.0600 (5)
C2	0.42602 (11)	1.1437 (2)	0.41164 (18)	0.0574 (5)
C3	0.41176 (11)	0.9723 (3)	0.44341 (18)	0.0579 (5)
C4	0.38435 (14)	1.4155 (3)	0.5219 (2)	0.0928 (8)
H4A	0.3560	1.4412	0.5946	0.139*
H4B	0.3608	1.4627	0.4501	0.139*
H4C	0.4338	1.4583	0.5310	0.139*
C5	0.34749 (13)	0.8499 (3)	0.6273 (2)	0.0718 (6)
H5A	0.3685	0.8675	0.7095	0.086*
H5B	0.3677	0.7490	0.5957	0.086*
C6	0.26484 (14)	0.8336 (3)	0.6378 (2)	0.0843 (8)
H6A	0.2445	0.9370	0.6638	0.101*
H6B	0.2541	0.7554	0.7025	0.101*
C7	0.22619 (15)	0.7826 (3)	0.5225 (2)	0.0900 (8)
H7A	0.2433	0.6750	0.5002	0.108*
H7B	0.2401	0.8557	0.4560	0.108*
C8	0.14125 (16)	0.7797 (4)	0.5319 (3)	0.1009 (9)
H8A	0.1279	0.7089	0.6001	0.121*
H8B	0.1245	0.8880	0.5530	0.121*
C9	0.10040 (16)	0.7269 (4)	0.4210 (3)	0.1090 (9)
H9A	0.1127	0.6141	0.4062	0.131*
H9B	0.1188	0.7885	0.3509	0.131*
C10	0.01784 (17)	0.7416 (4)	0.4219 (3)	0.1170 (10)
H10A	−0.0002	0.6749	0.4895	0.140*
H10B	0.0062	0.8531	0.4429	0.140*
C11	−0.0251 (2)	0.7008 (4)	0.3137 (3)	0.1316 (12)
H11A	−0.0147	0.5883	0.2947	0.158*
H11B	−0.0057	0.7646	0.2455	0.158*
C12	−0.1053 (2)	0.7196 (5)	0.3114 (4)	0.1429 (14)
H12A	−0.1252	0.6502	0.3758	0.171*
H12B	−0.1161	0.8304	0.3353	0.171*
C13	−0.1464 (3)	0.6868 (6)	0.1997 (5)	0.1794 (19)
H13A	−0.1252	0.7558	0.1361	0.215*
H13B	−0.1344	0.5763	0.1766	0.215*
C14	−0.2207 (2)	0.7006 (7)	0.1878 (5)	0.222 (3)
H14A	−0.2373	0.6402	0.1166	0.333*
H14B	−0.2337	0.8127	0.1775	0.333*
H14C	−0.2441	0.6588	0.2610	0.333*
N1	0.35613 (10)	1.1413 (2)	0.58418 (16)	0.0657 (5)
N2	0.37046 (9)	0.98167 (18)	0.54638 (15)	0.0595 (5)
N3	0.46775 (10)	1.1774 (2)	0.31735 (16)	0.0661 (5)
O1	0.43293 (9)	0.84926 (18)	0.39204 (14)	0.0772 (5)
O2	0.47788 (9)	1.33871 (19)	0.30532 (14)	0.0785 (5)
H2	0.5070 (12)	1.3428 (16)	0.2420 (16)	0.094*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0598 (13)	0.0601 (13)	0.0600 (12)	0.0000 (10)	0.0026 (10)	−0.0009 (11)
C2	0.0545 (13)	0.0668 (14)	0.0509 (12)	−0.0057 (10)	0.0037 (10)	0.0018 (10)
C3	0.0552 (12)	0.0685 (14)	0.0500 (12)	−0.0032 (10)	0.0036 (10)	−0.0025 (10)
C4	0.110 (2)	0.0661 (16)	0.103 (2)	0.0007 (14)	0.0284 (16)	−0.0057 (14)
C5	0.0791 (17)	0.0698 (14)	0.0667 (14)	−0.0035 (11)	0.0128 (12)	0.0041 (11)
C6	0.0851 (19)	0.0852 (17)	0.0827 (17)	−0.0104 (13)	0.0159 (14)	0.0072 (13)
C7	0.086 (2)	0.103 (2)	0.0810 (17)	0.0026 (14)	0.0038 (14)	−0.0040 (15)
C8	0.092 (2)	0.124 (2)	0.0875 (19)	−0.0123 (16)	0.0048 (16)	0.0023 (16)
C9	0.093 (2)	0.126 (2)	0.108 (2)	−0.0049 (17)	−0.0016 (18)	−0.0096 (19)
C10	0.096 (3)	0.148 (3)	0.107 (2)	−0.0172 (19)	0.0006 (19)	−0.009 (2)
C11	0.117 (3)	0.157 (3)	0.121 (3)	0.004 (2)	−0.030 (2)	−0.015 (2)
C12	0.102 (3)	0.188 (4)	0.138 (3)	−0.012 (2)	−0.030 (2)	−0.045 (3)
C13	0.111 (3)	0.233 (5)	0.195 (5)	0.012 (3)	−0.023 (3)	−0.057 (4)
C14	0.109 (4)	0.311 (7)	0.246 (6)	0.039 (4)	−0.024 (4)	−0.149 (5)
N1	0.0689 (12)	0.0641 (12)	0.0644 (11)	0.0024 (9)	0.0132 (9)	−0.0063 (9)
N2	0.0659 (11)	0.0554 (11)	0.0576 (10)	−0.0010 (8)	0.0177 (9)	0.0018 (8)
N3	0.0678 (12)	0.0647 (12)	0.0656 (12)	−0.0108 (9)	−0.0057 (9)	0.0070 (9)
O1	0.0963 (13)	0.0654 (10)	0.0703 (10)	0.0069 (8)	0.0236 (8)	−0.0107 (8)
O2	0.0848 (13)	0.0816 (12)	0.0693 (11)	−0.0046 (8)	0.0106 (8)	0.0062 (8)

Geometric parameters (Å, º)

C1—N1	1.291 (3)	C8—H8B	0.9700
C1—C2	1.461 (3)	C9—C10	1.487 (4)
C1—C4	1.473 (3)	C9—H9A	0.9700
C2—N3	1.296 (2)	C9—H9B	0.9700
C2—C3	1.478 (3)	C10—C11	1.432 (4)
C3—O1	1.218 (2)	C10—H10A	0.9700
C3—N2	1.340 (2)	C10—H10B	0.9700
C4—H4A	0.9600	C11—C12	1.447 (4)
C4—H4B	0.9600	C11—H11A	0.9700
C4—H4C	0.9600	C11—H11B	0.9700
C5—N2	1.455 (3)	C12—C13	1.431 (5)
C5—C6	1.495 (3)	C12—H12A	0.9700
C5—H5A	0.9700	C12—H12B	0.9700
C5—H5B	0.9700	C13—C14	1.343 (5)
C6—C7	1.477 (3)	C13—H13A	0.9700
C6—H6A	0.9700	C13—H13B	0.9700
C6—H6B	0.9700	C14—H14A	0.9600
C7—C8	1.529 (4)	C14—H14B	0.9600
C7—H7A	0.9700	C14—H14C	0.9600
C7—H7B	0.9700	N1—N2	1.403 (2)
C8—C9	1.462 (4)	N3—O2	1.349 (2)
C8—H8A	0.9700	O2—H2	0.86 (2)
N1—C1—C2	109.47 (18)	C10—C9—H9A	107.9
N1—C1—C4	121.54 (19)	C8—C9—H9B	107.9
C2—C1—C4	129.0 (2)	C10—C9—H9B	107.9
N3—C2—C1	135.3 (2)	H9A—C9—H9B	107.2
N3—C2—C3	119.25 (18)	C11—C10—C9	120.4 (3)
C1—C2—C3	105.43 (17)	C11—C10—H10A	107.2
O1—C3—N2	126.88 (19)	C9—C10—H10A	107.2
O1—C3—C2	129.59 (19)	C11—C10—H10B	107.2
N2—C3—C2	103.52 (18)	C9—C10—H10B	107.2
C1—C4—H4A	109.5	H10A—C10—H10B	106.9
C1—C4—H4B	109.5	C10—C11—C12	121.2 (3)
H4A—C4—H4B	109.5	C10—C11—H11A	107.0
C1—C4—H4C	109.5	C12—C11—H11A	107.0
H4A—C4—H4C	109.5	C10—C11—H11B	107.0
H4B—C4—H4C	109.5	C12—C11—H11B	107.0
N2—C5—C6	113.49 (19)	H11A—C11—H11B	106.8
N2—C5—H5A	108.9	C13—C12—C11	120.0 (4)
C6—C5—H5A	108.9	C13—C12—H12A	107.3
N2—C5—H5B	108.9	C11—C12—H12A	107.3
C6—C5—H5B	108.9	C13—C12—H12B	107.3
H5A—C5—H5B	107.7	C11—C12—H12B	107.3
C5—C6—C7	114.9 (2)	H12A—C12—H12B	106.9
C5—C6—H6A	108.5	C14—C13—C12	124.7 (4)
C7—C6—H6A	108.5	C14—C13—H13A	106.2
C5—C6—H6B	108.5	C12—C13—H13A	106.2
C7—C6—H6B	108.5	C14—C13—H13B	106.2
H6A—C6—H6B	107.5	C12—C13—H13B	106.2
C6—C7—C8	114.3 (2)	H13A—C13—H13B	106.4
C6—C7—H7A	108.7	C13—C14—H14A	109.5
C8—C7—H7A	108.7	C13—C14—H14B	109.5
C6—C7—H7B	108.7	H14A—C14—H14B	109.5
C8—C7—H7B	108.7	C13—C14—H14C	109.5
H7A—C7—H7B	107.6	H14A—C14—H14C	109.5
C9—C8—C7	116.4 (2)	H14B—C14—H14C	109.5
C9—C8—H8A	108.2	C1—N1—N2	108.13 (16)
C7—C8—H8A	108.2	C3—N2—N1	113.45 (16)
C9—C8—H8B	108.2	C3—N2—C5	127.78 (17)
C7—C8—H8B	108.2	N1—N2—C5	118.35 (17)
H8A—C8—H8B	107.3	C2—N3—O2	111.46 (17)
C8—C9—C10	117.6 (3)	N3—O2—H2	101.4 (9)
C8—C9—H9A	107.9

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1^i	0.86 (2)	1.81 (2)	2.671 (2)	179 (2)

Symmetry code: (i) −x+1, y+1/2, −z+1/2.