6,7-Di­chloro-2-methyl-3-phenyl­quinoxaline

Jones, M.W.; Aldridge, K.M.; Crundwell, G.

doi:10.1107/S2414314626008928

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 11| Part 9| September 2026| x260892

https://doi.org/10.1107/S2414314626008928

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6,7-Dichloro-2-methyl-3-phenylquinoxaline

Myron W. Jones,^a Katelyn M. Aldridge ^b and Guy Crundwell ^b ^*

^aDepartment of Chemistry, Southern Illinois University Edwardsville, Edwardsville, IL 62026-1652, USA, and ^bDepartment of Chemistry & Biochemistry, Central Connecticut State University, 1619 Stanley Street, New Britain, CT 06053, USA
^*Correspondence e-mail: [email protected]

Edited by M. Zeller, Purdue University, USA (Received 20 August 2026; accepted 27 August 2026; online 3 September 2026)

The title compound, C₁₅H₁₀Cl₂N₂, was synthesized using the acid catalyst NH₄HF₂ in a water/methanol solution. The dihedral angle between the phenyl ring and the quinoxaline unit is 39.80 (5)°. There is an intermolecular hydrogen-bonding-like interaction with a neighboring chlorine atom at a distance of 2.76 Å. The extended structure features offset-stacked quinoxaline units along the [100] direction.

Keywords: crystal structure; quinoxaline.

CCDC reference: 2583897

Structure description

In general, quinoxalines are of interest as potential antibacterial (Parhi et al., 2013 ), antimicrobial (Singh et al., 2010 ), and antifungal medicines (Tang et al., 2022 ) and therefore exploring their synthesis and structures are of interest. The title compound was synthesized via a condensation reaction of a diamine and diketone using a water/methanol solution containing the NH₄HF₂ catalyst (Lassagne et al., 2015 ).

The molecular structure is shown in Fig. 1. The quinoxaline ring system is essentially planar. The r.m.s. deviation of the dichloroquinoxaline unit (using atoms C1–C9, N1, N2, Cl1, and Cl2) is only 0.0604 Å. The quinoxaline moiety makes an angle of 39.80 (5)° with respect to the phenyl ring. There is a hydrogen-bonding-like interaction between a carbon hydrogen and a neighboring chlorine atom (Table 1). Molecules stack along the [100] direction of the unit cell (Fig. 2). Analysis of ring interactions using PLATON (Spek, 2009 ) indicats that the quinoxaline ring system (C1–C6,C8,C9,N1,N2) exhibits π⋯π stacking with interplanar spacings of 3.5039 (7) Å [for neighbor at (1 − x, −y, z)], 3.4022 (7) Å [for neighbor at ( $[{3\over 2}]$ − x, y, − $[{1\over 2}]$ + z)], and 3.3845 (7) Å [for neighbor at ( $[{3\over 2}]$ − x, y, 1/2 + z)] with slippages of 1.515, 3.582, and 3.565Å, respectively..

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2⋯Cl2ⁱ	0.95	2.76	3.704 (3)	175
Symmetry code: (i) .

Figure 1
A view of the title molecule. Hydrogen atoms are omitted and displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view of the unit-cell packing along the [100] direction.

Synthesis and crystallization

In a 50 mL Erlenmeyer flask, 1.49 g of 1-phenyl-1,2-propanedione (10.0 mmol) were added to 2 mL of H₂O and 20 mL of a 2.5 x 10⁻³ M methanol solution of NH₄HF₂ (Lassagne et al., 2015). To this mixture 1.78 g of 4,5-dichloro-1,2-phenylenediamine (10.0 mmol) were added. The solution was stirred for 24 h during which the product precipitated as a pale light-tan product. 2.65 g of crude product were isolated and recrysallized from methanol solution yielding 1.92 g of purified product (66%). Crystals for the diffraction study were isolated by the slow evaporation of 50/50 hexane/ethyl acetate solutions. M.p: 426 K; ¹H NMR (CDCl₃, 300 MHz): δ = 2.78 (s, 3H), 7.55 (m, 3H), 7.64 (m, 2H), 8.17 (s, 1H), 8.22 (s, 1H); ¹³C NMR (CDCl₃, 300 MHz): δ = 24.51, 128.85, 128.91, 129.16, 129.43, 129.84, 133.65, 134.12, 138.31, 139.77, 139.86, 153.98, 155.89.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₅H₁₀Cl₂N₂
M_r	289.15
Crystal system, space group	Orthorhombic, Aea2
Temperature (K)	150
a, b, c (Å)	13.7569 (4), 26.2508 (8), 7.1470 (2)
V (Å³)	2580.99 (13)
Z	8
Radiation type	Cu Kα
μ (mm⁻¹)	4.40
Crystal size (mm)	0.21 × 0.11 × 0.06

Data collection
Diffractometer	Bruker AXS D8 Quest
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.500, 0.754
No. of measured, independent and observed [I > 2σ(I)] reflections	35150, 2788, 2646
R_int	0.064
(sin θ/λ)_max (Å⁻¹)	0.640

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.029, 0.078, 1.11
No. of reflections	2788
No. of parameters	173
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.23, −0.28
Absolute structure	Flack x determined using 1146 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 )
Absolute structure parameter	0.004 (7)
Computer programs: APEX6 and SAINT (Bruker, 2026 ), SHELXT (Sheldrick, 2015a ), SHELXL2025/1 (Sheldrick, 2015b ), OLEX2 (Dolomanov et al., 2009 ), ORTEP-3 for Windows (Farrugia, 2012 ) and Mercury (Macrae et al., 2020 ).

Structural data

CCDC reference: 2583897

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314626008928/zl4103sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314626008928/zl4103Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314626008928/zl4103Isup3.cml

checkCIF report

Computing details top

6,7-Dichloro-2-methyl-3-phenylquinoxaline top

Crystal data top

C₁₅H₁₀Cl₂N₂	D_x = 1.488 Mg m⁻³
M_r = 289.15	Melting point: 426 K
Orthorhombic, Aea2	Cu Kα radiation, λ = 1.54178 Å
a = 13.7569 (4) Å	Cell parameters from 9889 reflections
b = 26.2508 (8) Å	θ = 3.4–80.1°
c = 7.1470 (2) Å	µ = 4.40 mm⁻¹
V = 2580.99 (13) Å³	T = 150 K
Z = 8	Plate, clear colourless
F(000) = 1184	0.21 × 0.11 × 0.06 mm

Data collection top

Bruker AXS D8 Quest diffractometer	2788 independent reflections
Radiation source: I-mu-S 3.0 microsource X-ray tube	2646 reflections with I > 2σ(I)
HELIOS multilayer Montel optics monochromator	R_int = 0.064
Detector resolution: 7.4074 pixels mm^-1	θ_max = 80.6°, θ_min = 3.4°
ω and phi scans	h = −17→17
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −33→33
T_min = 0.500, T_max = 0.754	l = −8→9
35150 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.029	H-atom parameters constrained
wR(F²) = 0.078	w = 1/[σ²(F_o²) + (0.0438P)² + 0.4866P] where P = (F_o² + 2F_c²)/3
S = 1.11	(Δ/σ)_max = 0.001
2788 reflections	Δρ_max = 0.23 e Å⁻³
173 parameters	Δρ_min = −0.28 e Å⁻³
1 restraint	Absolute structure: Flack x determined using 1146 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013)
Primary atom site location: dual	Absolute structure parameter: 0.004 (7)

Special details top

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

Refinement. Hydrogen atoms on sp² and sp³ carbons were placed at calculated positions with a C-H distance of 0.95 Å and 0.98 Å and were included in the refinement in riding motion approximation with U_iso = 1.2U_eq or 1.5U_eq of the carrier atom, respectively.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.37186 (15)	0.47901 (10)	0.6000 (4)	0.0262 (5)
C3	0.37034 (16)	0.56404 (10)	0.4771 (4)	0.0284 (5)
C10	0.37433 (14)	0.32221 (9)	0.4945 (4)	0.0242 (5)
C15	0.42966 (17)	0.30390 (9)	0.3437 (3)	0.0258 (5)
H15	0.466810	0.327048	0.270755	0.031*
N1	0.37599 (15)	0.44750 (9)	0.7518 (3)	0.0280 (5)
Cl1	0.36731 (4)	0.62940 (2)	0.51359 (11)	0.03628 (18)
C13	0.37601 (17)	0.21837 (10)	0.4054 (4)	0.0303 (5)
H13	0.377408	0.183049	0.376637	0.036*
C6	0.37267 (16)	0.45912 (9)	0.4161 (4)	0.0242 (5)
C12	0.31946 (17)	0.23595 (9)	0.5524 (3)	0.0306 (5)
H12	0.281249	0.212716	0.622943	0.037*
Cl2	0.37977 (5)	0.58627 (2)	0.10644 (10)	0.03599 (18)
C4	0.37379 (16)	0.54433 (10)	0.2935 (4)	0.0275 (5)
C5	0.37397 (16)	0.49310 (10)	0.2613 (4)	0.0267 (5)
H5	0.374956	0.480307	0.136961	0.032*
C8	0.37819 (16)	0.39822 (10)	0.7220 (4)	0.0250 (5)
C14	0.43071 (17)	0.25251 (10)	0.3002 (4)	0.0291 (5)
H14	0.468808	0.240553	0.198416	0.035*
N2	0.37302 (13)	0.40786 (8)	0.3852 (3)	0.0259 (5)
C2	0.36965 (16)	0.53235 (11)	0.6280 (4)	0.0294 (5)
H2	0.367700	0.545967	0.751059	0.035*
C9	0.37394 (14)	0.37773 (10)	0.5335 (4)	0.0232 (5)
C11	0.31853 (16)	0.28751 (8)	0.5968 (4)	0.0276 (4)
H11	0.279563	0.299277	0.697663	0.033*
C7	0.38880 (19)	0.36530 (10)	0.8927 (4)	0.0299 (5)
H7A	0.325163	0.351482	0.927622	0.045*
H7B	0.414578	0.385727	0.996143	0.045*
H7C	0.433567	0.337216	0.865550	0.045*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0260 (11)	0.0266 (13)	0.0260 (11)	0.0011 (8)	0.0006 (10)	−0.0021 (11)
C3	0.0277 (11)	0.0226 (13)	0.0350 (14)	−0.0003 (8)	0.0032 (9)	−0.0036 (10)
C10	0.0257 (10)	0.0242 (11)	0.0228 (12)	0.0017 (7)	−0.0034 (8)	−0.0012 (10)
C15	0.0287 (10)	0.0266 (11)	0.0221 (10)	0.0002 (9)	−0.0007 (8)	0.0006 (8)
N1	0.0320 (10)	0.0285 (11)	0.0235 (10)	0.0005 (8)	0.0006 (7)	−0.0029 (9)
Cl1	0.0454 (3)	0.0214 (3)	0.0421 (4)	−0.0014 (2)	0.0073 (3)	−0.0051 (2)
C13	0.0405 (13)	0.0215 (13)	0.0289 (13)	0.0001 (9)	−0.0036 (11)	−0.0014 (10)
C6	0.0256 (11)	0.0218 (12)	0.0252 (11)	0.0012 (8)	−0.0003 (8)	−0.0007 (10)
C12	0.0354 (12)	0.0287 (12)	0.0278 (13)	−0.0049 (9)	0.0008 (8)	0.0018 (8)
Cl2	0.0506 (3)	0.0257 (3)	0.0316 (3)	−0.0025 (2)	−0.0014 (3)	0.0041 (2)
C4	0.0281 (11)	0.0266 (13)	0.0278 (13)	−0.0002 (9)	−0.0006 (9)	0.0014 (10)
C5	0.0303 (12)	0.0256 (12)	0.0241 (13)	−0.0006 (9)	−0.0005 (8)	0.0000 (10)
C8	0.0249 (11)	0.0268 (12)	0.0234 (12)	0.0001 (8)	0.0003 (8)	−0.0026 (10)
C14	0.0332 (11)	0.0294 (11)	0.0246 (10)	0.0028 (10)	0.0008 (9)	−0.0028 (9)
N2	0.0281 (10)	0.0256 (12)	0.0240 (11)	0.0018 (7)	−0.0002 (8)	−0.0016 (8)
C2	0.0346 (12)	0.0270 (13)	0.0267 (14)	0.0006 (8)	0.0027 (9)	−0.0056 (10)
C9	0.0225 (9)	0.0252 (12)	0.0220 (11)	0.0005 (7)	0.0005 (8)	0.0001 (9)
C11	0.0292 (10)	0.0281 (11)	0.0257 (10)	0.0000 (8)	0.0019 (9)	−0.0018 (9)
C7	0.0374 (12)	0.0296 (14)	0.0226 (12)	0.0005 (10)	−0.0029 (10)	−0.0008 (10)

Geometric parameters (Å, º) top

C1—N1	1.365 (4)	C6—N2	1.364 (3)
C1—C6	1.415 (4)	C12—H12	0.9500
C1—C2	1.415 (4)	C12—C11	1.390 (3)
C3—Cl1	1.736 (3)	Cl2—C4	1.734 (3)
C3—C4	1.411 (4)	C4—C5	1.364 (4)
C3—C2	1.362 (4)	C5—H5	0.9500
C10—C15	1.404 (3)	C8—C9	1.451 (4)
C10—C9	1.484 (3)	C8—C7	1.502 (4)
C10—C11	1.397 (3)	C14—H14	0.9500
C15—H15	0.9500	N2—C9	1.323 (4)
C15—C14	1.385 (3)	C2—H2	0.9500
N1—C8	1.311 (3)	C11—H11	0.9500
C13—H13	0.9500	C7—H7A	0.9800
C13—C12	1.386 (4)	C7—H7B	0.9800
C13—C14	1.391 (4)	C7—H7C	0.9800
C6—C5	1.421 (3)

N1—C1—C6	121.0 (2)	C6—C5—H5	120.4
N1—C1—C2	119.2 (3)	C4—C5—C6	119.2 (2)
C6—C1—C2	119.8 (3)	C4—C5—H5	120.4
C4—C3—Cl1	120.2 (2)	N1—C8—C9	121.0 (2)
C2—C3—Cl1	119.0 (2)	N1—C8—C7	116.0 (2)
C2—C3—C4	120.8 (2)	C9—C8—C7	123.0 (2)
C15—C10—C9	118.8 (2)	C15—C14—C13	120.0 (2)
C11—C10—C15	118.4 (2)	C15—C14—H14	120.0
C11—C10—C9	122.7 (2)	C13—C14—H14	120.0
C10—C15—H15	119.6	C9—N2—C6	117.4 (2)
C14—C15—C10	120.8 (2)	C1—C2—H2	120.2
C14—C15—H15	119.6	C3—C2—C1	119.5 (2)
C8—N1—C1	118.0 (2)	C3—C2—H2	120.2
C12—C13—H13	120.0	C8—C9—C10	122.6 (2)
C12—C13—C14	119.9 (2)	N2—C9—C10	115.9 (2)
C14—C13—H13	120.0	N2—C9—C8	121.5 (2)
C1—C6—C5	119.5 (2)	C10—C11—H11	119.7
N2—C6—C1	121.0 (2)	C12—C11—C10	120.7 (2)
N2—C6—C5	119.6 (2)	C12—C11—H11	119.7
C13—C12—H12	119.9	C8—C7—H7A	109.5
C13—C12—C11	120.1 (2)	C8—C7—H7B	109.5
C11—C12—H12	119.9	C8—C7—H7C	109.5
C3—C4—Cl2	119.1 (2)	H7A—C7—H7B	109.5
C5—C4—C3	121.2 (2)	H7A—C7—H7C	109.5
C5—C4—Cl2	119.7 (2)	H7B—C7—H7C	109.5

C1—N1—C8—C9	−1.5 (3)	C6—N2—C9—C10	−179.98 (18)
C1—N1—C8—C7	176.4 (2)	C6—N2—C9—C8	−2.3 (3)
C1—C6—C5—C4	−0.4 (3)	C12—C13—C14—C15	0.8 (4)
C1—C6—N2—C9	−0.9 (3)	Cl2—C4—C5—C6	177.70 (17)
C3—C4—C5—C6	−1.3 (3)	C4—C3—C2—C1	−0.4 (4)
C10—C15—C14—C13	0.5 (3)	C5—C6—N2—C9	178.54 (19)
C15—C10—C9—C8	−139.0 (2)	C14—C13—C12—C11	−1.1 (4)
C15—C10—C9—N2	38.6 (3)	N2—C6—C5—C4	−179.9 (2)
C15—C10—C11—C12	1.3 (3)	C2—C1—N1—C8	−179.85 (19)
N1—C1—C6—C5	−176.4 (2)	C2—C1—C6—C5	1.7 (3)
N1—C1—C6—N2	3.1 (3)	C2—C1—C6—N2	−178.80 (19)
N1—C1—C2—C3	176.8 (2)	C2—C3—C4—Cl2	−177.28 (18)
N1—C8—C9—C10	−178.79 (18)	C2—C3—C4—C5	1.7 (4)
N1—C8—C9—N2	3.7 (3)	C9—C10—C15—C14	−178.8 (2)
Cl1—C3—C4—Cl2	2.5 (3)	C9—C10—C11—C12	178.5 (2)
Cl1—C3—C4—C5	−178.48 (17)	C11—C10—C15—C14	−1.5 (3)
Cl1—C3—C2—C1	179.85 (16)	C11—C10—C9—C8	43.8 (3)
C13—C12—C11—C10	0.0 (4)	C11—C10—C9—N2	−138.6 (2)
C6—C1—N1—C8	−1.7 (3)	C7—C8—C9—C10	3.4 (3)
C6—C1—C2—C3	−1.3 (3)	C7—C8—C9—N2	−174.1 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···Cl2ⁱ	0.95	2.76	3.704 (3)	175

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

Acknowledgements

This work was supported by a CCSU-AAUP grant. All data were collected at Purdue University by Dr Matthias Zeller as part of the American Crystallographic Association Summer Course (2026). Dr Zeller also assisted with the refinement.

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