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Acta Cryst. (2009). E65, o2082    [ doi:10.1107/S1600536809030074 ]

(S)-Ethyl 2-[4-(6-chloroquinoxalin-2-yloxy)phenoxy]propanoate

J. Hu, G. Chen, L. Guo, J. Wang and Y. Xu

Abstract top

In the molecule of the title compound, C19H17ClN2O4, the quinoxaline ring system is planar [maximum deviation = 0.013 (3) Å] and oriented at a dihedral angle of 80.18 (3)° with respect to the benzene ring. In the crystal structure, intermolecular C-H...N interactions link molecules into chains. [pi]-[pi] contacts between the quinoxaline systems [centroid-centroid distance = 3.654 (1) Å] may further stabilize the structure.

Comment top

The title compound has a potent selective herbicidal activity against annual and perennial grass weeds (Sakata et al., 1985). We report herein its crystal structure.

In the molecule of the title compound (Fig. 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges. Rings A (C6-C11), B (C13-C18) and C (N1/N2/C12/C13/C18/C19) are, of course, planar, and they are oriented at dihedral angles of A/B = 80.21 (3), A/C = 80.07 (3) and B/C = 0.66 (3) °. The quinoxaline ring system is planar with a maximum deviation of -0.013 (3) Å for atom N1.

In the crystal structure, intermolecular C-H···N interactions link the molecules into chains (Fig. 2), in which they may be effective in the stabilization of the structure. The π–π contact between the quinoxaline rings, Cg2—Cg3i [symmetry code: (i) x, y - 1, z, where Cg2 and Cg3 are centroids of the rings B (C13-C18) and C (N1/N2/C12/C13/C18/C19), respectively] may further stabilize the structure, with centroid-centroid distance of 3.654 (1) Å.

Related literature top

The title compound has potent selective herbicidal activity against annual and perennial grass weeds, see: Sakata et al. (1985). For bond-length data, see: Allen et al. (1987);

Experimental top

For the preparation of the title compound, thionyl chloride (3.7 ml, 50 mmol) was added in dropwise to (S)-2-(4-(6-chloroquinoxalin-2-yloxy)phenoxy)propanoate acid (3.72 g, 10 mmol) in an ice bath (263 K). After refluxing for 5 h, the mixture was cooled to room temperature, and excess thionyl chloride was removed by reduced pressure distillation. Then, the residue was dissolved in a solution of ethanol (4.9 ml, 80 mmol) and pyridine (2.5 ml, 30 mmol). The solid residue was extracted with hexane (40 ml) and hexane was distilled off. Crystals suitable for X-ray analysis were formed after 8 d in ethyl acetate by slow evaporation at room temperature.

Refinement top

H atoms were positioned geometrically with C-H = 0.93, 0.98, 0.97 and 0.96 Å, for aromatic, methine, methylene and methyl H atoms, respectively, and constrained to ride on their parent atoms, with Uiso(H) = xUeq(C), where x = 1.5 for methyl H and x = 1.2 for aromatic H atoms.

Computing details top

Data collection: CAD-4 Software (Enraf–Nonius, 1985); cell refinement: CAD-4 Software (Enraf–Nonius, 1985); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. A partial packing diagram of the title compound. Hydrogen bonds are shown as dashed lines.
(S)-Ethyl 2-[4-(6-chloroquinoxalin-2-yloxy)phenoxy]propanoate top
Crystal data top
C19H17ClN2O4F(000) = 388
Mr = 372.80Dx = 1.361 Mg m−3
Monoclinic, P21Melting point: 350 K
Hall symbol: P 2ybMo Kα radiation, λ = 0.71073 Å
a = 9.970 (2) ÅCell parameters from 25 reflections
b = 4.4760 (9) Åθ = 9–12°
c = 20.450 (4) ŵ = 0.24 mm−1
β = 94.54 (3)°T = 294 K
V = 909.7 (3) Å3Needle, colorless
Z = 20.30 × 0.20 × 0.10 mm
Data collection top
Enraf–Nonius CAD-4
diffractometer		1254 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.052
graphiteθmax = 25.4°, θmin = 2.0°
ω/2θ scansh = −11→11
Absorption correction: ψ scan
(North et al., 1968)		k = −5→0
Tmin = 0.932, Tmax = 0.977l = −24→24
3762 measured reflections3 standard reflections every 120 min
1898 independent reflections intensity decay: 1%
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.050H-atom parameters constrained
wR(F2) = 0.155 w = 1/[σ2(Fo2) + (0.085P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.00(Δ/σ)max < 0.001
1898 reflectionsΔρmax = 0.17 e Å−3
235 parametersΔρmin = −0.19 e Å−3
1 restraintAbsolute structure: Flack (1983), 932 Friedel pairs
Primary atom site location: structure-invariant direct methodsFlack parameter: −0.02 (18)
Crystal data top
C19H17ClN2O4V = 909.7 (3) Å3
Mr = 372.80Z = 2
Monoclinic, P21Mo Kα radiation
a = 9.970 (2) ŵ = 0.24 mm−1
b = 4.4760 (9) ÅT = 294 K
c = 20.450 (4) Å0.30 × 0.20 × 0.10 mm
β = 94.54 (3)°
Data collection top
Enraf–Nonius CAD-4
diffractometer		1254 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)		Rint = 0.052
Tmin = 0.932, Tmax = 0.977θmax = 25.4°
3762 measured reflections3 standard reflections every 120 min
1898 independent reflections intensity decay: 1%
Refinement top
R[F2 > 2σ(F2)] = 0.050H-atom parameters constrained
wR(F2) = 0.155Δρmax = 0.17 e Å−3
S = 1.00Δρmin = −0.19 e Å−3
1898 reflectionsAbsolute structure: Flack (1983), 932 Friedel pairs
235 parametersFlack parameter: −0.02 (18)
1 restraint
Special details top

Experimental. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R– factors based on ALL data will be even larger.

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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Cl0.50826 (14)0.9066 (5)0.08796 (7)0.0921 (6)
O11.8615 (3)0.4503 (12)0.3878 (2)0.0925 (14)
O21.7523 (4)0.0871 (12)0.3367 (2)0.0956 (14)
O31.5198 (3)0.2389 (10)0.38949 (16)0.0730 (11)
O41.2147 (3)0.1148 (12)0.15458 (16)0.0838 (13)
N10.9132 (4)0.2496 (12)0.05649 (17)0.0616 (11)
N21.0378 (4)0.4196 (12)0.18081 (17)0.0563 (10)
C12.0926 (5)0.474 (2)0.4119 (4)0.131 (3)
H1B2.17930.41380.39930.196*
H1C2.08030.39980.45510.196*
H1D2.08710.68820.41200.196*
C21.9882 (5)0.353 (2)0.3656 (3)0.095 (2)
H2B1.99880.42820.32180.115*
H2C1.99280.13700.36480.115*
C31.7536 (5)0.3000 (15)0.3698 (3)0.0657 (15)
C41.6313 (4)0.4380 (16)0.3988 (2)0.0710 (15)
H4A1.60920.63080.37790.085*
C51.6551 (6)0.476 (2)0.4726 (3)0.107 (3)
H5A1.57710.56450.48930.161*
H5B1.73160.60290.48240.161*
H5C1.67160.28410.49270.161*
C61.4468 (4)0.2317 (14)0.3298 (2)0.0582 (13)
C71.3386 (5)0.0408 (14)0.3263 (2)0.0656 (14)
H7A1.3203−0.06820.36330.079*
C81.2570 (5)0.0074 (15)0.2696 (2)0.0715 (17)
H8A1.1837−0.12170.26770.086*
C91.2861 (5)0.1681 (15)0.2160 (2)0.0637 (15)
C101.3937 (5)0.3564 (15)0.2181 (3)0.0720 (15)
H10A1.41190.46390.18080.086*
C111.4758 (5)0.3883 (16)0.2752 (3)0.0718 (15)
H11A1.55000.51470.27650.086*
C121.0919 (5)0.2395 (14)0.1409 (2)0.0612 (13)
C130.9127 (4)0.5295 (12)0.1580 (2)0.0517 (12)
C140.8466 (5)0.7268 (13)0.1979 (2)0.0586 (13)
H14A0.88590.78110.23890.070*
C150.7228 (5)0.8395 (14)0.1757 (2)0.0658 (15)
H15A0.67830.97150.20170.079*
C160.6646 (5)0.7562 (14)0.1148 (2)0.0626 (14)
C170.7261 (5)0.5646 (14)0.0749 (2)0.0614 (14)
H17A0.68520.51360.03400.074*
C180.8516 (4)0.4457 (12)0.0964 (2)0.0509 (12)
C191.0293 (5)0.1538 (15)0.0790 (2)0.0646 (15)
H19A1.07460.02160.05340.078*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl0.0714 (9)0.1061 (14)0.0958 (11)0.0193 (10)−0.0124 (7)0.0154 (11)
O10.056 (2)0.079 (3)0.141 (3)−0.003 (2)0.003 (2)−0.029 (3)
O20.092 (3)0.083 (3)0.111 (3)0.010 (3)0.002 (2)−0.037 (3)
O30.063 (2)0.087 (3)0.067 (2)−0.018 (2)−0.0070 (16)0.000 (2)
O40.065 (2)0.115 (4)0.070 (2)0.028 (3)−0.0046 (17)−0.022 (2)
N10.061 (2)0.071 (3)0.051 (2)−0.001 (3)−0.0001 (18)0.002 (2)
N20.054 (2)0.066 (3)0.049 (2)0.001 (2)−0.0021 (16)−0.001 (2)
C10.062 (4)0.123 (8)0.205 (8)0.012 (5)−0.004 (4)−0.024 (7)
C20.066 (3)0.099 (5)0.123 (5)0.013 (4)0.016 (3)0.007 (5)
C30.061 (3)0.067 (4)0.068 (3)0.001 (3)−0.003 (2)0.000 (3)
C40.055 (3)0.067 (4)0.089 (4)−0.005 (3)−0.004 (2)−0.014 (3)
C50.078 (4)0.156 (8)0.087 (4)−0.006 (5)0.001 (3)−0.055 (5)
C60.048 (2)0.064 (3)0.063 (3)−0.002 (3)0.004 (2)−0.006 (3)
C70.058 (3)0.074 (4)0.064 (3)−0.009 (3)0.004 (2)−0.001 (3)
C80.054 (3)0.091 (5)0.070 (3)−0.010 (3)0.009 (2)−0.013 (3)
C90.051 (3)0.077 (4)0.062 (3)0.014 (3)−0.004 (2)−0.016 (3)
C100.073 (3)0.070 (4)0.072 (3)0.002 (3)0.002 (3)0.008 (3)
C110.061 (3)0.074 (4)0.080 (3)−0.017 (3)−0.002 (2)0.011 (4)
C120.060 (3)0.070 (4)0.053 (3)0.000 (3)0.002 (2)0.002 (3)
C130.052 (2)0.056 (3)0.047 (2)−0.007 (2)−0.0007 (19)0.005 (2)
C140.061 (3)0.057 (3)0.056 (3)−0.002 (3)−0.001 (2)0.004 (3)
C150.069 (3)0.062 (4)0.067 (3)0.007 (3)0.010 (2)0.004 (3)
C160.055 (3)0.066 (4)0.065 (3)−0.001 (3)−0.002 (2)0.015 (3)
C170.065 (3)0.069 (4)0.049 (2)−0.006 (3)−0.010 (2)0.011 (3)
C180.056 (2)0.051 (3)0.045 (2)−0.010 (3)0.0043 (19)0.003 (2)
C190.072 (3)0.076 (4)0.047 (2)0.001 (3)0.006 (2)−0.010 (3)
Geometric parameters (Å, °) top
Cl—C161.746 (5)C5—H5C0.9600
O1—C21.443 (6)C6—C111.370 (7)
O1—C31.298 (7)C6—C71.373 (7)
O2—C31.168 (7)C7—C81.372 (6)
O3—C41.426 (6)C7—H7A0.9300
O3—C61.371 (5)C8—C91.361 (8)
O4—C91.414 (6)C8—H8A0.9300
O4—C121.355 (6)C9—C101.363 (8)
N1—C181.375 (6)C10—C111.379 (7)
N1—C191.285 (6)C10—H10A0.9300
N2—C121.294 (7)C11—H11A0.9300
N2—C131.386 (6)C12—C191.420 (6)
C1—C21.455 (9)C13—C141.401 (7)
C1—H1B0.9600C13—C181.407 (6)
C1—H1C0.9600C14—C151.376 (7)
C1—H1D0.9600C14—H14A0.9300
C2—H2B0.9700C15—C161.383 (7)
C2—H2C0.9700C15—H15A0.9300
C3—C41.528 (8)C16—C171.362 (7)
C4—C51.519 (7)C17—C181.398 (6)
C4—H4A0.9800C17—H17A0.9300
C5—H5A0.9600C19—H19A0.9300
C5—H5B0.9600
C3—O1—C2118.8 (5)C6—C7—H7A119.2
C6—O3—C4119.1 (4)C9—C8—C7118.3 (5)
C12—O4—C9119.8 (4)C9—C8—H8A120.9
C19—N1—C18115.6 (4)C7—C8—H8A120.9
C12—N2—C13114.7 (4)C8—C9—C10121.3 (5)
C2—C1—H1B109.5C8—C9—O4120.1 (5)
C2—C1—H1C109.5C10—C9—O4118.1 (5)
C2—C1—H1D109.5C9—C10—C11120.2 (5)
H1B—C1—H1C109.5C9—C10—H10A119.9
H1B—C1—H1D109.5C11—C10—H10A119.9
H1C—C1—H1D109.5C6—C11—C10119.2 (5)
O1—C2—C1106.4 (6)C6—C11—H11A120.4
O1—C2—H2B110.4C10—C11—H11A120.4
C1—C2—H2B110.4N2—C12—O4122.8 (4)
O1—C2—H2C110.4N2—C12—C19123.7 (5)
C1—C2—H2C110.4O4—C12—C19113.5 (5)
H2B—C2—H2C108.6N2—C13—C14118.7 (4)
O2—C3—O1124.0 (6)N2—C13—C18121.4 (4)
O2—C3—C4125.6 (6)C14—C13—C18119.9 (4)
O1—C3—C4110.4 (5)C15—C14—C13119.4 (4)
O3—C4—C5105.1 (5)C15—C14—H14A120.3
O3—C4—C3109.5 (5)C13—C14—H14A120.3
C5—C4—C3111.4 (4)C14—C15—C16119.9 (5)
O3—C4—H4A110.3C14—C15—H15A120.1
C5—C4—H4A110.3C16—C15—H15A120.1
C3—C4—H4A110.3C17—C16—C15122.2 (5)
C4—C5—H5A109.5C17—C16—Cl119.2 (4)
C4—C5—H5B109.5C15—C16—Cl118.6 (5)
H5A—C5—H5B109.5C16—C17—C18119.1 (4)
C4—C5—H5C109.5C16—C17—H17A120.4
H5A—C5—H5C109.5C18—C17—H17A120.4
H5B—C5—H5C109.5N1—C18—C17119.2 (4)
C11—C6—O3125.7 (5)N1—C18—C13121.3 (4)
C11—C6—C7119.5 (5)C17—C18—C13119.5 (5)
O3—C6—C7114.9 (5)N1—C19—C12123.3 (5)
C8—C7—C6121.5 (5)N1—C19—H19A118.3
C8—C7—H7A119.2C12—C19—H19A118.3
C3—O1—C2—C1−157.4 (6)C13—N2—C12—C19−1.0 (8)
C2—O1—C3—O20.7 (9)C9—O4—C12—N23.3 (9)
C2—O1—C3—C4179.7 (5)C9—O4—C12—C19−176.8 (5)
C6—O3—C4—C5159.6 (5)C12—N2—C13—C14−179.9 (5)
C6—O3—C4—C3−80.7 (6)C12—N2—C13—C180.4 (7)
O2—C3—C4—O310.5 (8)N2—C13—C14—C15179.5 (5)
O1—C3—C4—O3−168.5 (4)C18—C13—C14—C15−0.8 (7)
O2—C3—C4—C5126.3 (7)C13—C14—C15—C160.4 (8)
O1—C3—C4—C5−52.7 (8)C14—C15—C16—C17−0.3 (8)
C4—O3—C6—C114.3 (8)C14—C15—C16—Cl−179.3 (4)
C4—O3—C6—C7−177.8 (5)C15—C16—C17—C180.6 (8)
C11—C6—C7—C8−1.3 (9)Cl—C16—C17—C18179.7 (4)
O3—C6—C7—C8−179.3 (5)C19—N1—C18—C17178.8 (5)
C6—C7—C8—C90.3 (8)C19—N1—C18—C13−0.9 (7)
C7—C8—C9—C100.4 (8)C16—C17—C18—N1179.3 (5)
C7—C8—C9—O4172.5 (5)C16—C17—C18—C13−1.0 (7)
C12—O4—C9—C881.4 (7)N2—C13—C18—N10.5 (7)
C12—O4—C9—C10−106.3 (6)C14—C13—C18—N1−179.2 (5)
C8—C9—C10—C11−0.1 (9)N2—C13—C18—C17−179.2 (5)
O4—C9—C10—C11−172.4 (6)C14—C13—C18—C171.1 (7)
O3—C6—C11—C10179.3 (5)C18—N1—C19—C120.4 (8)
C7—C6—C11—C101.5 (9)N2—C12—C19—N10.6 (9)
C9—C10—C11—C6−0.9 (9)O4—C12—C19—N1−179.2 (5)
C13—N2—C12—O4178.9 (5)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C19—H19A···N1i0.932.573.396 (7)149
Symmetry codes: (i) −x+2, y−1/2, −z.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C19—H19A···N1i0.932.573.396 (7)149
Symmetry codes: (i) −x+2, y−1/2, −z.
Acknowledgements top

The authors thank the Center of Testing and Analysis, Nanjing University for support.

references
References top

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North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351–359.

Sakata, G., Makino, K., Morimoto, K., Ikai, T. & Hasebe, S. (1985). Nippon Noyaku Gakkaishi, 10, 69–73.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.