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Acta Crystallogr Sect E Struct Rep Online. 2008 July 1; 64(Pt 7): o1191.
Published online 2008 June 7. doi:  10.1107/S1600536808016103
PMCID: PMC2961730

rac-(4aR,8aR)-2,3-Diphenyl-4a,5,6,7,8,8a-hexa­hydro­quinoxaline

Abstract

The structure of the title racemic compound, C20H20N2, shows close similarity to that of the enanti­omerically pure (4aR,8aR)-2,3-diphenyl-4a,5,6,7,8,8a-hexa­hydro­quinoxaline [Wang & Ye (2008 [triangle]). Acta Cryst. E64, o359–o359]. The similarity applies to the unit-cell parameters as well as to the packing of the constituent mol­ecules. Similar packing is conditioned by a lack of directed inter­molecular inter­actions such as hydrogen bonds in either structure.

Related literature

For examples of the synthesis of non-centrosymmetric solid materials by the reaction of chiral organic ligands and inorganic salts, see: Qu et al. (2004 [triangle]). For geometric parameters of C=N bonds, see: Figuet et al. (2001 [triangle]); Kennedy & Reglinski (2001 [triangle]). For our previous work regarding the enanti­omerically pure (4aR,8aR)-2,3-diphenyl-4a,5,6,7,8,8a-hexa­hydro­quin­ox­aline, see: Wang & Ye (2008 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-64-o1191-scheme1.jpg

Experimental

Crystal data

  • C20H20N2
  • M r = 288.38
  • Orthorhombic, An external file that holds a picture, illustration, etc.
Object name is e-64-o1191-efi1.jpg
  • a = 15.278 (3) Å
  • b = 18.388 (4) Å
  • c = 5.6638 (11) Å
  • V = 1591.2 (5) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.07 mm−1
  • T = 293 (2) K
  • 0.25 × 0.15 × 0.10 mm

Data collection

  • Rigaku SCXmini diffractometer
  • Absorption correction: multi-scan (CrystalClear; Rigaku, 2005 [triangle]) T min = 0.831, T max = 1.000 (expected range = 0.825–0.993)
  • 16117 measured reflections
  • 2004 independent reflections
  • 1558 reflections with I > 2σ(I)
  • R int = 0.071

Refinement

  • R[F 2 > 2σ(F 2)] = 0.047
  • wR(F 2) = 0.100
  • S = 1.10
  • 2004 reflections
  • 199 parameters
  • 1 restraint
  • H-atom parameters constrained
  • Δρmax = 0.13 e Å−3
  • Δρmin = −0.17 e Å−3

Data collection: CrystalClear (Rigaku, 2005 [triangle]); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: SHELXTL (Sheldrick, 2008 [triangle]); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808016103/fb2093sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808016103/fb2093Isup2.hkl

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

Acknowledgments

This work was supported by a Start-up Grant awarded to HYY by Southeast University.

supplementary crystallographic information

Comment

Presence of chiral centres in organic ligands is very important for design and synthesis of noncentrosymmetric or chiral coordination polymers which exhibit desirable physical properties such as a ferroelectric behaviour (Qu et al., 2004). We have recently reported the crystal structure of the enantiomerically pure ligand (4aR,8aR)-2,3-diphenyl-4a,5,6,7,8,8a-hexahydroquinoxaline (Wang & Ye, 2008). As a part of our ongoing investigations in this field we have determined the crystal structure of the title compound, rac-(4aR,8aR)-2,3- diphenyl-4a,5,6,7,8,8a-hexahydroquinoxaline.

The title compound can be regarded as a derivative of hexahydroquinoxaline by substitution of two H atoms in each of the positions 2 and 3 by the phenyl rings. The heterocyclic ring of the quinoxaline system has a twist-boat configuration, while the cyclohexane ring has a chair configuration. The torsion angle N2—C1—C6—N1 is -58.3 (3)°. The C═N double bonds (C7═N1, 1.272 (2) Å; C14═N2, 1.279 (2) Å) are in the range of 1.27–1.38 Å that have been found in other Schiff base complexes (Figuet et al., 2001; Kennedy & Reglinski, 2001; Wang & Ye, 2008). C7, C14 show typical sp2 geometry environment. Comparing the bond angles around sp2 N atoms (N1, N2) with those around the sp2 C atoms (C7, C14), the latter are somewhat more close to 120°. N1C8C7C14 and N2C15C14C7 are almost coplanar with the mean deviations equal to 0.0119 and 0.0052 Å, respectively. The angle (29.76 (14)°) between the planes of N1C7C8C14 and N2C7C14C15 is very close to that (29.65 (14)°) in the enantiomerically pure compound (4aR,8aR)-2,3-diphenyl-4a,5,6,7,8,8a-hexahydroquinoxaline (Wang & Ye, 2008). The angle (64.3 (1)°) between both phenyl rings in the title structure equals within the precision of the experiments to that (64.3 (1)°) of the enantiomerically pure compound (4aR,8aR)-2,3-diphenyl-4a,5,6,7,8,8a-hexahydroquinoxaline.

The title racemic compound crystallizes in the space group of Pna21. Figs. 2 and 3 contain the respective views of the unit cells of the title compound and its enantiomerically pure counterpart (Wang & Ye, 2008)). [The enantiomerically pure structure in Fig. 3 has been obtained by the following transformations of the published data (Wang & Ye, 2008): (a,b,c)2 = (a,b,c)1(0 1 0/0 0 1/1 0 0) followed by the shift of the origin by -1/4 1/2 -1/4 with the corresponding change in the translational parts of the symmetry operators. (0 1 0/0 0 1/1 0 0) is the transformation matrix where each triplet of the numbers corresponds to its row.]

In spite of the fact that a half of the molecules in the title structure are the opposite enantiomers (Fig. 2) in contrast to the structure composed of the enantiomers of one kind in Wang & Ye (2008) (Fig. 3) both structures look alike when wieved along the shortest unit-cell axis. It can not be excluded that both enantiomers form solid solutions in some composition interval. The experiments that would confirm the hypothesis about the formation of the solid solutions are going to be carried out in near future. The melting point of the enantiomerically pure structure (Wang & Ye, 2008) is 194–198°C.

(Note: The setting P21nb is directly related to that of the reported structure of the enantiomerically pure compound (Wang & Ye, 2008). In the setting P21nb the unit cell axes are ordered according to their length from the minimal to the maximal.)

Experimental

rac-(1R,2R/1S,2S)-diaminocyclohexane was obtained from Adrich. The title compound was prepared by an analogous procedure to that regarding the enantiomerically pure (4aR,8aR)-2,3-diphenyl-4a,5,6,7,8,8a-hexahydroquinoxaline (Wang & Ye, 2008) using rac-1,2-diaminocyclohexane instead of (-)-(1R,2R)-diaminocyclohexane. Yellow block-like crystals, suitable for X-ray analysis, were obtained by slow evaporation of the ethanol solution of the crude product.

Refinement

All the H atoms were discernible in difference electron-density map. Nevertheless, they were placed to the idealed positons and refined in a riding atom approximation constrainsts as following: Cmethine—Hmethine = 0.98; Cmethylene—Hmethylene = 0.97; Caryl—Haryl = 0.93 Å; UisoH = 1.2 UeqC in all the cases. In the absence of significant resonant scattering effects, 1639 Friedel pairs were merged.

Figures

Fig. 1.
The drawing of one enantiomer with RR configuration of the title compound. The atomic numbering scheme is given. The displacement ellipsoids are drawn at the 30% probability level.
Fig. 2.
The view of the title compound along the axis c (cf. Fig. 3).
Fig. 3.
The view of the enantiomerically pure compound (Wang & Ye, 2008) along the axis c (cf. Fig. 2) after suitable transformations (see the comment section).

Crystal data

C20H20N2Dx = 1.204 Mg m3
Mr = 288.38Melting point = 447–453 K
Orthorhombic, Pna21Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2nCell parameters from 13431 reflections
a = 15.278 (3) Åθ = 3.3–27.5°
b = 18.388 (4) ŵ = 0.07 mm1
c = 5.6638 (11) ÅT = 293 K
V = 1591.2 (5) Å3Block, pale yellow
Z = 40.25 × 0.15 × 0.10 mm
F(000) = 616

Data collection

Rigaku SCXmini diffractometer2004 independent reflections
Radiation source: fine-focus sealed tube1558 reflections with I > 2σ(I)
graphiteRint = 0.071
Detector resolution: 13.6612 pixels mm-1θmax = 27.5°, θmin = 3.5°
ω scansh = −19→19
Absorption correction: multi-scan (CrystalClear; Rigaku, 2005)k = −23→23
Tmin = 0.831, Tmax = 1.000l = −7→7
16117 measured reflections

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.047Hydrogen site location: difference Fourier map
wR(F2) = 0.100H-atom parameters constrained
S = 1.10w = 1/[σ2(Fo2) + (0.0344P)2 + 0.1949P] where P = (Fo2 + 2Fc2)/3
2004 reflections(Δ/σ)max < 0.001
199 parametersΔρmax = 0.13 e Å3
1 restraintΔρmin = −0.17 e Å3
80 constraints

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.
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 > 2µ(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)

xyzUiso*/Ueq
C10.59529 (17)0.36737 (13)0.4260 (5)0.0432 (6)
H1A0.56430.39880.53770.052*
C20.55215 (16)0.29231 (13)0.4296 (6)0.0531 (7)
H2A0.58490.25940.32900.064*
H2B0.55330.27310.58900.064*
C30.45847 (19)0.29648 (16)0.3444 (7)0.0626 (9)
H3A0.42410.32430.45660.075*
H3B0.43410.24780.33660.075*
C40.4523 (2)0.33176 (15)0.1036 (7)0.0666 (10)
H4A0.39130.33670.05960.080*
H4B0.48050.3008−0.01230.080*
C50.49552 (18)0.40639 (14)0.1012 (7)0.0572 (8)
H5A0.49380.4262−0.05750.069*
H5B0.46350.43910.20410.069*
C60.58925 (16)0.40112 (12)0.1829 (5)0.0413 (6)
H6A0.62140.37020.07180.050*
C70.69908 (15)0.47944 (12)0.3141 (5)0.0362 (6)
C80.73733 (14)0.55333 (12)0.3446 (5)0.0362 (6)
C90.72510 (16)0.60532 (13)0.1701 (5)0.0429 (6)
H9A0.69670.59290.03070.051*
C100.75498 (16)0.67548 (14)0.2028 (6)0.0482 (7)
H10A0.74640.71000.08490.058*
C110.79687 (17)0.69479 (14)0.4061 (6)0.0514 (7)
H11A0.81640.74230.42690.062*
C120.81003 (18)0.64389 (14)0.5800 (6)0.0532 (7)
H12A0.83910.65680.71800.064*
C130.78012 (17)0.57348 (13)0.5501 (5)0.0453 (7)
H13A0.78880.53940.66900.054*
C140.73617 (15)0.41439 (13)0.4428 (5)0.0389 (6)
C150.83132 (16)0.40920 (13)0.4971 (5)0.0397 (6)
C160.89364 (17)0.43624 (14)0.3435 (6)0.0484 (7)
H16A0.87610.45960.20580.058*
C170.98203 (18)0.42881 (15)0.3928 (7)0.0583 (8)
H17A1.02340.44680.28750.070*
C181.0086 (2)0.39503 (15)0.5962 (7)0.0592 (9)
H18A1.06800.39030.62960.071*
C190.94719 (19)0.36810 (15)0.7508 (6)0.0577 (8)
H19A0.96520.34550.88940.069*
C200.85886 (18)0.37447 (14)0.7016 (6)0.0510 (7)
H20A0.81780.35540.80580.061*
N10.63098 (13)0.47350 (10)0.1870 (4)0.0419 (5)
N20.68676 (14)0.36140 (11)0.5019 (5)0.0475 (6)

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
C10.0398 (14)0.0371 (14)0.0528 (17)0.0033 (11)0.0011 (13)0.0030 (13)
C20.0423 (15)0.0418 (15)0.075 (2)0.0004 (11)0.0043 (16)0.0103 (16)
C30.0468 (17)0.0485 (17)0.092 (3)−0.0020 (13)−0.0008 (17)0.0044 (18)
C40.0511 (17)0.0546 (18)0.094 (3)−0.0083 (14)−0.0200 (19)−0.0023 (19)
C50.0517 (18)0.0482 (17)0.072 (2)0.0002 (13)−0.0168 (16)0.0042 (16)
C60.0405 (14)0.0346 (13)0.0488 (16)0.0011 (10)−0.0028 (13)−0.0006 (13)
C70.0373 (13)0.0325 (13)0.0386 (13)0.0001 (10)−0.0002 (12)0.0016 (11)
C80.0330 (13)0.0325 (12)0.0430 (14)0.0020 (10)0.0019 (12)0.0010 (12)
C90.0396 (14)0.0402 (14)0.0488 (17)0.0032 (11)−0.0021 (13)0.0051 (13)
C100.0448 (14)0.0376 (14)0.0622 (18)0.0005 (11)0.0078 (16)0.0099 (14)
C110.0486 (16)0.0362 (14)0.069 (2)−0.0068 (12)0.0058 (16)−0.0051 (15)
C120.0586 (18)0.0447 (16)0.0564 (19)−0.0031 (13)−0.0055 (15)−0.0093 (15)
C130.0526 (16)0.0373 (14)0.0461 (17)0.0031 (12)−0.0030 (14)0.0015 (12)
C140.0399 (14)0.0354 (13)0.0413 (14)0.0026 (11)−0.0009 (12)0.0014 (12)
C150.0413 (14)0.0286 (12)0.0492 (16)0.0052 (11)−0.0062 (13)0.0004 (11)
C160.0467 (15)0.0428 (15)0.0557 (18)0.0070 (12)0.0001 (14)0.0034 (14)
C170.0424 (16)0.0504 (17)0.082 (3)0.0058 (13)0.0053 (16)−0.0001 (18)
C180.0454 (17)0.0453 (16)0.087 (2)0.0093 (13)−0.0155 (17)−0.0097 (17)
C190.0598 (18)0.0473 (16)0.066 (2)0.0118 (15)−0.0198 (17)−0.0003 (15)
C200.0545 (17)0.0424 (14)0.0561 (18)0.0018 (13)−0.0059 (16)0.0058 (14)
N10.0428 (12)0.0337 (10)0.0493 (13)0.0000 (9)−0.0053 (11)0.0040 (10)
N20.0430 (12)0.0421 (12)0.0572 (15)0.0013 (10)−0.0049 (12)0.0115 (11)

Geometric parameters (Å, °)

C1—N21.466 (3)C9—C101.381 (3)
C1—C61.513 (4)C9—H9A0.9300
C1—C21.530 (3)C10—C111.364 (4)
C1—H1A0.9800C10—H10A0.9300
C2—C31.512 (4)C11—C121.373 (4)
C2—H2A0.9700C11—H11A0.9300
C2—H2B0.9700C12—C131.384 (3)
C3—C41.513 (5)C12—H12A0.9300
C3—H3A0.9700C13—H13A0.9300
C3—H3B0.9700C14—N21.277 (3)
C4—C51.522 (4)C14—C151.489 (3)
C4—H4A0.9700C15—C161.382 (4)
C4—H4B0.9700C15—C201.388 (4)
C5—C61.508 (4)C16—C171.386 (4)
C5—H5A0.9700C16—H16A0.9300
C5—H5B0.9700C17—C181.370 (5)
C6—N11.476 (3)C17—H17A0.9300
C6—H6A0.9800C18—C191.376 (5)
C7—N11.270 (3)C18—H18A0.9300
C7—C81.489 (3)C19—C201.383 (4)
C7—C141.511 (3)C19—H19A0.9300
C8—C131.385 (4)C20—H20A0.9300
C8—C91.387 (3)
N2—C1—C6110.8 (2)C13—C8—C7121.8 (2)
N2—C1—C2109.8 (2)C9—C8—C7119.6 (2)
C6—C1—C2110.8 (2)C10—C9—C8120.2 (3)
N2—C1—H1A108.4C10—C9—H9A119.9
C6—C1—H1A108.4C8—C9—H9A119.9
C2—C1—H1A108.4C11—C10—C9120.8 (3)
C3—C2—C1111.0 (2)C11—C10—H10A119.6
C3—C2—H2A109.4C9—C10—H10A119.6
C1—C2—H2A109.4C10—C11—C12119.8 (2)
C3—C2—H2B109.4C10—C11—H11A120.1
C1—C2—H2B109.4C12—C11—H11A120.1
H2A—C2—H2B108.0C11—C12—C13120.1 (3)
C2—C3—C4111.6 (3)C11—C12—H12A119.9
C2—C3—H3A109.3C13—C12—H12A119.9
C4—C3—H3A109.3C12—C13—C8120.6 (3)
C2—C3—H3B109.3C12—C13—H13A119.7
C4—C3—H3B109.3C8—C13—H13A119.7
H3A—C3—H3B108.0N2—C14—C15118.3 (2)
C3—C4—C5111.6 (3)N2—C14—C7120.6 (2)
C3—C4—H4A109.3C15—C14—C7121.1 (2)
C5—C4—H4A109.3C16—C15—C20118.8 (2)
C3—C4—H4B109.3C16—C15—C14121.3 (2)
C5—C4—H4B109.3C20—C15—C14119.9 (2)
H4A—C4—H4B108.0C15—C16—C17120.6 (3)
C6—C5—C4110.5 (2)C15—C16—H16A119.7
C6—C5—H5A109.5C17—C16—H16A119.7
C4—C5—H5A109.5C18—C17—C16120.2 (3)
C6—C5—H5B109.5C18—C17—H17A119.9
C4—C5—H5B109.5C16—C17—H17A119.9
H5A—C5—H5B108.1C17—C18—C19119.7 (3)
N1—C6—C5110.92 (19)C17—C18—H18A120.1
N1—C6—C1109.2 (2)C19—C18—H18A120.1
C5—C6—C1111.3 (2)C18—C19—C20120.5 (3)
N1—C6—H6A108.4C18—C19—H19A119.8
C5—C6—H6A108.4C20—C19—H19A119.8
C1—C6—H6A108.4C19—C20—C15120.2 (3)
N1—C7—C8117.8 (2)C19—C20—H20A119.9
N1—C7—C14120.8 (2)C15—C20—H20A119.9
C8—C7—C14121.3 (2)C7—N1—C6116.1 (2)
C13—C8—C9118.5 (2)C14—N2—C1115.4 (2)
N2—C1—C6—N1−58.1 (3)

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FB2093).

References

  • Figuet, M., Averbuch-Pouchot, M. T., Moulinet d’Hardemare, A. D. & Jarjayes, O. (2001). Eur. J. Inorg. Chem.2001, 2089–2096.
  • Kennedy, A. R. & Reglinski, J. (2001). Acta Cryst. E57, o1027–o1028.
  • Qu, Z.-R., Zhao, H., Wang, Y.-P., Wang, X.-S., Ye, Q., Li, Y.-H., Xiong, R.-G., Abrahams, B. H., Liu, Z.-G., Xue, Z.-L. & You, X.-Z. (2004). Chem. Eur. J.10, 54–60. [PubMed]
  • Rigaku (2005). CrystalClear Rigaku Corporation, Tokyo, Japan.
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Wang, G.-X. & Ye, H.-Y. (2008). Acta Cryst. E64, o359. [PMC free article] [PubMed]

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