Redetermination of 1,4-dimethoxy­benzene

Abstract

The structure of the centrosymmetric title compound, C₈H₁₀O₂, originally determined by Goodwin et al. [Acta Cryst.(1950), 3, 279–284], has been redetermined to modern standards of precision to aid in its use as a model compound for ¹³C chemical-shift tensor measurements in single-crystal NMR studies. In the crystal structure, a C—H⋯O inter­action helps to establish the packing.

Related literature

For previous structural studies of the title compound, see: Goodwin et al. (1950 ▶); Carter et al. (1988 ▶).

Experimental

Crystal data

• C₈H₁₀O₂

• M _r = 138.16

• Orthorhombic,

• a = 7.1757 (3) Å

• b = 6.2769 (2) Å

• c = 16.5573 (7) Å

• V = 745.76 (5) ų

• Z = 4

• Mo Kα radiation

• μ = 0.09 mm⁻¹

• T = 150 (1) K

• 0.33 × 0.30 × 0.23 mm

Data collection

• Nonius KappaCCD diffractometer

• Absorption correction: multi-scan (DENZO–SMN; Otwinowski & Minor, 1997 ▶) T _min = 0.972, T _max = 0.980

• 1510 measured reflections

• 847 independent reflections

• 732 reflections with I > 2σ(I)

• R _int = 0.013

Refinement

• R[F ² > 2σ(F ²)] = 0.037

• wR(F ²) = 0.101

• S = 1.09

• 847 reflections

• 66 parameters

• All H-atom parameters refined

• Δρ_max = 0.19 e Å⁻³

• Δρ_min = −0.16 e Å⁻³

Data collection: COLLECT (Hooft, 1998 ▶); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997 ▶); data reduction: DENZO–SMN; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: WinGX (Farrugia, 1999 ▶) and ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: publCIF (Westrip, 2009 ▶).

Supplementary Material

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

Enhanced figure: interactive version of Fig. 1

Enhanced figure: interactive version of Fig. 2

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C4—H4A⋯O1i	1.019 (16)	2.552 (15)	3.4381 (15)	145.1 (10)

Symmetry code: (i) .

supplementary crystallographic information

Comment

Large single-crystals of organic compounds can be challenging to grow. Substituted methoxybenzenes are one exception and single-crystals on the order of centimeters can be obtained. The ease of crystal growth has enabled substituted methoxybenzenes to be studied by single-crystal NMR experiments. Pioneering work on the development of the two-dimensional single-crystal chemical-shift chemical-shift correlation NMR experiments utilized large crystals of 1,4-dimethoxybenzene (Carter et al., 1988). In 1950 Goodwin et al. obtained the first X-ray diffraction structure for 1,4-dimethoxybenzene. This structure (R-factor = 0.12) is shown in Fig. 1 and reported an unusual H–C–C angle of 75.7°, which prompted the acquisition of a second structure (Carter et al., 1988). More typical H–C–C angles were observed with this new refinement and this structure (R-factor = 0.067) was used to assign tensor orientations in the single-crystal NMR analysis. Inadvertently, the second structure was never submitted to the Cambridge Crystallographic database. Here, the acquisition of a third structure is reported to correct this oversight. The new structure (R-factor = 0.038) is shown in Fig. 2. The unit-cell and space group of the previous studies are confirmed.

Acquisition of this third, more accurate, structure is beneficial to NMR studies because the ¹³C chemical shift tensor data of 1,4-dimethoxybenzene continue to serve as a standard to evaluate new chemical-shift tensor measurement methods as well as to assess electronic structure methods for computing magnetic properties of molecules.

Refinement

The H atoms were located in difference maps and their positions and U_iso values were freely refined.

Figures

Fig. 1.

The structure of (I) according to Goodwin et al. (1950).

Fig. 2.

The redetermined structure of (I) from the present study.

Crystal data

C8H10O2	Dx = 1.231 Mg m−3
Mr = 138.16	Melting point: 329 K
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 13221 reflections
a = 7.1757 (3) Å	θ = 1.0–27.5°
b = 6.2769 (2) Å	µ = 0.09 mm−1
c = 16.5573 (7) Å	T = 150 K
V = 745.76 (5) Å3	Prism, colorless
Z = 4	0.33 × 0.30 × 0.23 mm
F(000) = 296

Data collection

Nonius KappaCCD diffractometer	847 independent reflections
Radiation source: fine-focus sealed tube	732 reflections with I > 2σ(I)
graphite	Rint = 0.013
φ and ω scans	θmax = 27.5°, θmin = 3.8°
Absorption correction: multi-scan (DENZO–SMN; Otwinowski & Minor, 1997)	h = −9→9
Tmin = 0.972, Tmax = 0.980	k = −8→8
1510 measured reflections	l = −21→21

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.037	Hydrogen site location: difference Fourier map
wR(F2) = 0.101	All H-atom parameters refined
S = 1.09	w = 1/[σ2(Fo2) + (0.0517P)2 + 0.1487P] where P = (Fo2 + 2Fc2)/3
847 reflections	(Δ/σ)max < 0.001
66 parameters	Δρmax = 0.19 e Å−3
0 restraints	Δρmin = −0.16 e Å−3
none constraints

Special details

Experimental. The program DENZO-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm (Fox & Holmes, 1966) which effectively corrects for absorption effects. High redundancy data were used in the scaling program hence the 'multi-scan' code word was used. No transmission coefficients are available from the program (only scale factors for each frame). The scale factors in the experimental table are calculated from the 'size' command in the SHELXL97 input file.

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 > 2σ(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 (Ų)

	x	y	z	Uiso*/Ueq
O1	0.01305 (11)	0.15781 (13)	0.15601 (4)	0.0315 (3)
C2	0.09537 (13)	−0.10269 (16)	0.06126 (6)	0.0257 (3)
C3	−0.09472 (14)	0.18955 (17)	0.01604 (6)	0.0264 (3)
C1	0.00160 (12)	0.08587 (17)	0.07767 (6)	0.0243 (3)
C4	−0.0849 (2)	0.3490 (2)	0.17534 (8)	0.0410 (3)
H2	0.1619 (17)	−0.175 (2)	0.1048 (8)	0.033 (3)*
H3	−0.1604 (18)	0.319 (2)	0.0253 (7)	0.031 (3)*
H4A	−0.061 (2)	0.375 (2)	0.2352 (10)	0.050 (4)*
H4B	−0.221 (3)	0.323 (2)	0.1672 (9)	0.057 (5)*
H4C	−0.036 (2)	0.470 (3)	0.1413 (11)	0.056 (4)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
O1	0.0387 (5)	0.0328 (5)	0.0231 (4)	0.0040 (3)	−0.0018 (3)	−0.0031 (3)
C2	0.0249 (5)	0.0268 (5)	0.0255 (5)	0.0015 (4)	−0.0017 (4)	0.0043 (4)
C3	0.0259 (5)	0.0244 (5)	0.0288 (6)	0.0029 (4)	0.0012 (4)	0.0014 (4)
C1	0.0241 (5)	0.0267 (5)	0.0220 (5)	−0.0028 (4)	0.0012 (3)	0.0007 (4)
C4	0.0534 (8)	0.0377 (7)	0.0321 (6)	0.0092 (6)	−0.0004 (5)	−0.0104 (5)

Geometric parameters (Å, °)

O1—C1	1.3759 (12)	C3—C1	1.3937 (14)
O1—C4	1.4269 (14)	C3—H3	0.953 (13)
C2—C1	1.3883 (15)	C4—H4A	1.020 (16)
C2—C3i	1.3912 (15)	C4—H4B	0.998 (18)
C2—H2	0.977 (13)	C4—H4C	1.010 (18)
C3—C2i	1.3912 (15)
C1—O1—C4	117.26 (9)	O1—C1—C3	124.51 (10)
C1—C2—C3i	120.83 (9)	C2—C1—C3	119.68 (10)
C1—C2—H2	119.4 (7)	O1—C4—H4A	105.8 (8)
C3i—C2—H2	119.8 (7)	O1—C4—H4B	108.4 (9)
C2i—C3—C1	119.48 (10)	H4A—C4—H4B	108.8 (12)
C2i—C3—H3	118.7 (8)	O1—C4—H4C	109.7 (9)
C1—C3—H3	121.8 (8)	H4A—C4—H4C	111.2 (12)
O1—C1—C2	115.81 (9)	H4B—C4—H4C	112.6 (12)
C4—O1—C1—C2	−178.76 (10)	C3i—C2—C1—C3	0.10 (16)
C4—O1—C1—C3	1.69 (15)	C2i—C3—C1—O1	179.44 (9)
C3i—C2—C1—O1	−179.47 (9)	C2i—C3—C1—C2	−0.10 (16)

Symmetry codes: (i) −x, −y, −z.

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4A···O1ii	1.019 (16)	2.552 (15)	3.4381 (15)	145.1 (10)

Symmetry codes: (ii) −x, y+1/2, −z+1/2.