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ISSN: 2414-3146

2,3-Di­ethyl­benzo[g]quinoxaline

aCentral Connecticut State University, Department of Chemistry & Biochemistry, 1619 Stanley Street, New Britain, CT 06050, USA, and bDepartment of Chemistry & Biochemistry, Central Connecticut State University, 1619 Stanley Street, New Britain, CT 06053, USA
*Correspondence e-mail: crundwellg@ccsu.edu

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 1 April 2020; accepted 1 April 2020; online 7 April 2020)

The title compound, C16H16N2, was synthesized by dispersing 3,4-hexa­nedione in a methanol–water solution containing the acid catalyst NH4HF2, then adding 1,2-di­aminona­phthalene. The fused-ring system of the title compound is close to planar (r.m.s. deviation = 0.028 Å); one of the pendant methyl C atoms lies close to the ring plane [deviation = 0.071 (2) Å; N—C—C—C = −0.27 (18)°] whereas the other is significantly displaced [–1.7136 (18) Å; 91.64 (16)°]. The mol­ecules pack in space group I[\overline{4}] in a distinctive criss-cross motif supported by numerous aromatic ππ stacking inter­actions [shortest centroid–centroid separation = 3.5805 (6) Å].

3D view (loading...)
[Scheme 3D1]
Chemical scheme
[Scheme 1]

Structure description

The bond lengths and angles in the title compound fall within their expected values and the C3–C14/N1/N2 fused-ring system is close to planar (r.m.s. deviation = 0.028 Å). The C1 methyl atom lies close to the ring plane [deviation = 0.071 (2) Å; N1—C3—C2—C1 = −0.027 (16)°] whereas C16 is significantly displaced [deviation = −1.7136 (18) Å; N2—C14—C15—C16 = 91.64 (16)°] (Fig. 1[link]).

[Figure 1]
Figure 1
A view of the title compound with displacement ellipsoids drawn at the 50% probability level.

In the crystal, the molecles pack in a distinctive criss-cross motif (Fig. 2[link]) in space group I[\overline{4}] with stacks of mol­ecules propagating in the [001] direction. Numerous aromatic ππ stacking inter­actions help to consolidate the packing [shortest centroid–centroid separation = 3.5805 (6) Å].

[Figure 2]
Figure 2
A view of the unit cell of the title compound along [001].

Synthesis and crystallization

2,3-Di­ethyl­benzo[g]quinoxaline, C16H16N2, was prepared using the method used by Lassagne et al. (2015[Lassagne, F., Chevallier, F., Roisnel, T., Dorcet, V., Mongin, F. & Domingo, L. R. (2015). Synthesis, 47, 2680-2689.]) to create 2,3-di­aryl­pyrido­pyrazines. In a 50-ml Erlenmeyer flask equipped with a stir bar, 10.0 mmol of hexa­nedione (1.14 g) was dispersed in 20 ml of a 2.5 × 10−3 M NH4HF2 solution in MeOH and 2 ml of distilled water. To that stirred solution, 10.0 mmol of 1,2-naphthalenedi­amine (1.58 g) was added. The solution was allowed to stir overnight despite evidence of product after the first hour: 1.44 grams of a pale whitish powder was filtered and washed with two 2 ml aliquots of ice-cold methanol (60.9% yield). The crude product was mostly pure by NMR but was further purified by recrystallization from a 50:50 methanol/toluene solution (1.11 g recovered, 47.0% yield overall). (m.p. 411 K) ATR–IR (cm−1) 2981, 2934, 1703, 1575, 1455, 1351, 1325, 910, 889, 754; 1H NMR (300 MHz, CDCl3): δ 8.58 (s, 1H), 8.07 (m, 1H), 7.55 (m, 1H) 3.09 (q, 2H), 1.49 (t, 3H); 13C (300 MHz, CDCl3): δ 158.14, 138.06, 133.24, 128.35, 126.57, 126.15, 28.63, 12.07. Crystals for the diffraction experiment were grown from slow evaporation of a methyl­ene chloride solution. FTIR, 1H NMR, and 13C NMR spectra are given as supporting information.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1[link]. The absolute structure of the crystal chosen for data collection was indeterminate in the refinement reported here.

Table 1
Experimental details

Crystal data
Chemical formula C16H16N2
Mr 236.31
Crystal system, space group Tetragonal, I[\overline{4}]
Temperature (K) 293
a, c (Å) 13.93535 (18), 13.1629 (3)
V3) 2556.16 (7)
Z 8
Radiation type Mo Kα
μ (mm−1) 0.07
Crystal size (mm) 0.39 × 0.33 × 0.27
 
Data collection
Diffractometer Rigaku Xcalibur, Sapphire3
Absorption correction Multi-scan (CrysAlis PRO; Rigaku, 2018[Rigaku (2018). CrysAlis PRO. Rigaku Inc., Tokyo, Japan.])
Tmin, Tmax 0.922, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections 31103, 4779, 3869
Rint 0.031
(sin θ/λ)max−1) 0.778
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.048, 0.136, 1.04
No. of reflections 4779
No. of parameters 165
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.28, −0.14
Computer programs: CrysAlis PRO (Rigaku, 2018[Rigaku (2018). CrysAlis PRO. Rigaku Inc., Tokyo, Japan.]), SHELXM (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), SHELXL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]) and OLEX2 (Dolomanov et al., 2009[Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339-341.]).

Structural data


Computing details top

Data collection: CrysAlis PRO (Rigaku, 2018); cell refinement: CrysAlis PRO (Rigaku, 2018); data reduction: CrysAlis PRO (Rigaku, 2018); program(s) used to solve structure: SHELXM (Sheldrick, 2008); program(s) used to refine structure: SHELXL (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

2,3-Diethylbenzo[g]quinoxaline top
Crystal data top
C16H16N2Melting point: 411 K
Mr = 236.31Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4Cell parameters from 7488 reflections
a = 13.93535 (18) Åθ = 4.6–31.8°
c = 13.1629 (3) ŵ = 0.07 mm1
V = 2556.16 (7) Å3T = 293 K
Z = 8Block, white
F(000) = 10080.39 × 0.33 × 0.27 mm
Dx = 1.228 Mg m3
Data collection top
Rigaku Xcalibur, Sapphire3
diffractometer
4779 independent reflections
Radiation source: fine-focus sealed X-ray tube, Enhance (Mo) X-ray Source3869 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.031
Detector resolution: 16.1790 pixels mm-1θmax = 33.6°, θmin = 4.3°
ω scansh = 2121
Absorption correction: multi-scan
(CrysAlisPro; Rigaku, 2018)
k = 2121
Tmin = 0.922, Tmax = 1.000l = 2019
31103 measured reflections
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)] = 0.048H-atom parameters constrained
wR(F2) = 0.136 w = 1/[σ2(Fo2) + (0.0756P)2 + 0.2732P]
where P = (Fo2 + 2Fc2)/3
S = 1.04(Δ/σ)max < 0.001
4779 reflectionsΔρmax = 0.28 e Å3
165 parametersΔρmin = 0.14 e Å3
0 restraintsAbsolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Primary atom site location: dualAbsolute structure parameter: 0 (2)
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. 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.

H atoms were included in calculated positions with C—H = 0.93–0.97 Å and refined as riding atoms with Uiso = 1.2Ueq(C) or 1.5Ueq(methyl C). Reflections affected by the beam stop were omitted from the refinement.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.29561 (13)1.16936 (12)0.44274 (13)0.0600 (4)
H1A0.32061.11100.47110.090*
H1B0.33331.22270.46590.090*
H1C0.23021.17760.46400.090*
C20.29974 (10)1.16422 (10)0.32887 (12)0.0493 (3)
H2A0.27931.22560.30160.059*
H2B0.36601.15460.30870.059*
C30.23964 (8)1.08656 (8)0.28133 (10)0.0379 (2)
C40.13277 (8)0.96118 (8)0.29463 (9)0.0328 (2)
C50.07941 (9)0.89899 (9)0.35476 (9)0.0378 (2)
H50.08150.90470.42510.045*
C60.02254 (8)0.82781 (8)0.31001 (9)0.0360 (2)
C70.03189 (10)0.76181 (10)0.36928 (12)0.0475 (3)
H70.03100.76610.43980.057*
C80.08527 (12)0.69247 (11)0.32317 (15)0.0567 (4)
H80.11990.64930.36270.068*
C90.08872 (12)0.68520 (11)0.21668 (15)0.0608 (4)
H90.12530.63720.18670.073*
C100.03930 (10)0.74736 (11)0.15731 (12)0.0515 (3)
H100.04300.74210.08700.062*
C110.01854 (8)0.82097 (9)0.20173 (10)0.0369 (2)
C120.07119 (8)0.88458 (9)0.14191 (9)0.0380 (2)
H120.06760.88060.07150.046*
C130.12889 (8)0.95376 (8)0.18678 (8)0.0333 (2)
C140.23818 (8)1.07610 (9)0.17124 (10)0.0381 (2)
C150.30438 (11)1.13340 (11)0.10459 (12)0.0522 (3)
H15A0.27631.13980.03750.063*
H15B0.31231.19720.13280.063*
C160.40207 (12)1.08493 (14)0.09594 (16)0.0684 (5)
H16A0.42991.07860.16230.103*
H16B0.39451.02250.06610.103*
H16C0.44341.12310.05390.103*
N10.18907 (7)1.03067 (7)0.34033 (9)0.0388 (2)
N20.18387 (7)1.01278 (8)0.12633 (8)0.0388 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0616 (8)0.0543 (8)0.0641 (10)0.0115 (7)0.0117 (8)0.0176 (7)
C20.0434 (6)0.0432 (7)0.0613 (9)0.0115 (5)0.0068 (6)0.0058 (6)
C30.0336 (5)0.0337 (5)0.0463 (6)0.0024 (4)0.0068 (5)0.0029 (4)
C40.0293 (5)0.0313 (5)0.0377 (5)0.0020 (4)0.0033 (4)0.0039 (4)
C50.0381 (5)0.0396 (6)0.0358 (5)0.0027 (4)0.0006 (4)0.0041 (4)
C60.0306 (5)0.0336 (5)0.0439 (6)0.0011 (4)0.0009 (4)0.0024 (4)
C70.0441 (6)0.0445 (6)0.0539 (8)0.0059 (5)0.0057 (6)0.0018 (6)
C80.0494 (8)0.0470 (7)0.0738 (11)0.0151 (6)0.0073 (7)0.0010 (7)
C90.0510 (8)0.0494 (8)0.0820 (12)0.0184 (6)0.0056 (8)0.0122 (8)
C100.0467 (7)0.0515 (7)0.0563 (8)0.0122 (6)0.0081 (6)0.0113 (6)
C110.0302 (5)0.0360 (5)0.0446 (6)0.0000 (4)0.0049 (4)0.0058 (4)
C120.0365 (6)0.0423 (6)0.0353 (5)0.0022 (4)0.0059 (4)0.0042 (4)
C130.0292 (5)0.0340 (5)0.0368 (5)0.0016 (4)0.0041 (4)0.0006 (4)
C140.0341 (5)0.0356 (5)0.0445 (6)0.0005 (4)0.0041 (5)0.0067 (5)
C150.0550 (8)0.0455 (7)0.0561 (8)0.0093 (6)0.0022 (6)0.0152 (6)
C160.0504 (8)0.0754 (11)0.0794 (11)0.0118 (8)0.0130 (8)0.0169 (9)
N10.0364 (5)0.0390 (5)0.0409 (5)0.0054 (4)0.0047 (4)0.0056 (4)
N20.0384 (5)0.0402 (5)0.0378 (5)0.0016 (4)0.0044 (4)0.0044 (4)
Geometric parameters (Å, º) top
C1—H1A0.9600C8—H80.9300
C1—H1B0.9600C8—C91.406 (3)
C1—H1C0.9600C9—H90.9300
C1—C21.502 (2)C9—C101.355 (2)
C2—H2A0.9700C10—H100.9300
C2—H2B0.9700C10—C111.4296 (16)
C2—C31.5047 (17)C11—C121.3943 (17)
C3—C141.4566 (18)C12—H120.9300
C3—N11.3062 (16)C12—C131.3873 (15)
C4—C51.3894 (15)C13—N21.3772 (15)
C4—C131.4245 (15)C14—C151.5027 (18)
C4—N11.3839 (13)C14—N21.3042 (16)
C5—H50.9300C15—H15A0.9700
C5—C61.3997 (16)C15—H15B0.9700
C6—C71.4247 (17)C15—C161.524 (2)
C6—C111.4296 (17)C16—H16A0.9600
C7—H70.9300C16—H16B0.9600
C7—C81.362 (2)C16—H16C0.9600
H1A—C1—H1B109.5C10—C9—C8120.77 (14)
H1A—C1—H1C109.5C10—C9—H9119.6
H1B—C1—H1C109.5C9—C10—H10119.7
C2—C1—H1A109.5C9—C10—C11120.63 (14)
C2—C1—H1B109.5C11—C10—H10119.7
C2—C1—H1C109.5C6—C11—C10118.53 (12)
C1—C2—H2A108.4C12—C11—C6120.01 (10)
C1—C2—H2B108.4C12—C11—C10121.46 (12)
C1—C2—C3115.34 (12)C11—C12—H12119.8
H2A—C2—H2B107.5C13—C12—C11120.42 (10)
C3—C2—H2A108.4C13—C12—H12119.8
C3—C2—H2B108.4C12—C13—C4119.79 (10)
C14—C3—C2119.57 (11)N2—C13—C4120.75 (10)
N1—C3—C2118.81 (11)N2—C13—C12119.44 (10)
N1—C3—C14121.62 (10)C3—C14—C15121.27 (11)
C5—C4—C13120.14 (10)N2—C14—C3121.79 (11)
N1—C4—C5119.49 (10)N2—C14—C15116.81 (12)
N1—C4—C13120.37 (10)C14—C15—H15A109.5
C4—C5—H5119.8C14—C15—H15B109.5
C4—C5—C6120.35 (10)C14—C15—C16110.89 (12)
C6—C5—H5119.8H15A—C15—H15B108.1
C5—C6—C7121.91 (11)C16—C15—H15A109.5
C5—C6—C11119.27 (11)C16—C15—H15B109.5
C7—C6—C11118.82 (11)C15—C16—H16A109.5
C6—C7—H7119.8C15—C16—H16B109.5
C8—C7—C6120.31 (13)C15—C16—H16C109.5
C8—C7—H7119.8H16A—C16—H16B109.5
C7—C8—H8119.5H16A—C16—H16C109.5
C7—C8—C9120.93 (14)H16B—C16—H16C109.5
C9—C8—H8119.5C3—N1—C4117.69 (10)
C8—C9—H9119.6C14—N2—C13117.71 (10)
 

Acknowledgements

This research was funded by a CCSU–AAUP research grant.

References

First citationDolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationLassagne, F., Chevallier, F., Roisnel, T., Dorcet, V., Mongin, F. & Domingo, L. R. (2015). Synthesis, 47, 2680–2689.  Web of Science CrossRef CAS Google Scholar
First citationRigaku (2018). CrysAlis PRO. Rigaku Inc., Tokyo, Japan.  Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar

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