1,4,5,8-Tetra­methoxy­anthracene

The structure of the title compound, C₁₈H₁₈O₄, consists of separate centrosymmetric planar mol­ecules arranged in columns parallel to the monoclinic unique axis. The normal to the mean molecular plane lies at 55.4° to the unique axis, giving adjacent columns with alternating stacking directions. The mean deviation of all non-H atoms from the least-squares molecular plane is 0.064 Å. Bond lengths in the aromatic rings range from 1.347 (2) to 1.440 (2) Å and the two unique Me-O bond distances are 1.418 (2) and 1.419 (2) Å.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.052
• wR factor = 0.140
• Data-to-parameter ratio = 17.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


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S1. Comment

There has been considerable ongoing research involving the electrochemistry of compounds incorporating multiple quinones. Some of these compounds are anthracene derivatives (Jozefiak et al., 1989), while others are based on triptycene architecture (Doerner et al., 1998; Jozefiak et al., 1989; Quast & Fuchsbauer, 1986; Russel & Suleman, 1981). 1,4,5,8-Tetramethoxyanthracene (1,4,5,8-TMA), (I), has been used as an intermediate in the syntheses of some of these compounds. During research involving the synthesis of molecules that can undergo photoinduced electron transfer, 1,4,5,8-TMA was used as a synthetic intermediate.

The structure of (I) consists of individual molecules having no unusually short intermolecular contacts. The packing is in columns parallel to the b axis. Each molecule is planar, as shown in Fig. 1, with an average deviation from the least-squares plane through all non-H atoms of 0.064 Å, and a maximum of 0.164 Å by the methyl atom C3'. The molecule is slightly distorted, since aromatic-ring angles deviate from 120°, ranging from 118.44 (13)° at C2—C7—C6 to 122.27 (14)° at C1—C7—C6. Perhaps the most interesting feature of this structure is the tilt of the bond angles at the methoxy groups. Both methoxy groups bend toward each other down the length of the molecule, with facing MeO-ϕ angles of 113.85 (13) and 114.16 (13)°. These distortions presumably originate from packing effects in the solid state.

S2. Experimental

The title compound was prepared from bromo-2,5-dimethoxybenzene using a synthesis developed by Fleming & Mah (1975) and refined by Olofson and co-workers (Fitzgerald et al., 1992). Their method is a one-step synthesis using 2,2,6,6-tetramethylpiperidine in refluxing tetrahydrofuran and provides moderate yields.

S3. Refinement

H atoms were located in the difference Fourier maps, then positioned geometrically and allowed to ride on their respective parent atoms. [Is this added text acceptable?]

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Bruker, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. Displacement ellipsoid plot shown at the 50% probability level, viewed perpendicular to the mean plane [symmetry code: (i) 2 − x, −y, 1 − z].

1,4,5,8-tetramethoxyanthracene

Crystal data

C18H18O4	F(000) = 316
Mr = 298.32	Dx = 1.342 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 11.1715 (9) Å	Cell parameters from 2419 reflections
b = 5.9994 (5) Å	θ = 3.1–27.4°
c = 11.7159 (10) Å	µ = 0.09 mm^−1
β = 109.961 (2)°	T = 298 K
V = 738.05 (11) Å^3	Plate, clear pale yellow
Z = 2	0.41 × 0.27 × 0.11 mm

Data collection

Bruker SMART APEX diffractometer	1159 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.043
Graphite monochromator	θmax = 27.5°, θmin = 2.2°
ω scans	h = −14→14
6951 measured reflections	k = −7→7
1696 independent reflections	l = −15→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.140	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0745P)^2] where P = (Fo^2 + 2Fc^2)/3
1696 reflections	(Δ/σ)max < 0.001
100 parameters	Δρmax = 0.20 e Å^−3
0 restraints	Δρmin = −0.33 e Å^−3

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 > 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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.93841 (14)	−0.0031 (2)	0.58475 (13)	0.0388 (4)
H1A	0.8971	−0.0051	0.6415	0.047*
C2	0.90694 (13)	0.1619 (2)	0.49551 (13)	0.0371 (4)
C3	0.81446 (15)	0.3322 (2)	0.48978 (14)	0.0424 (4)
O3	0.75942 (12)	0.31463 (18)	0.57774 (11)	0.0567 (4)
C3'	0.6846 (2)	0.4977 (4)	0.5903 (2)	0.0732 (6)
H3'A	0.6511	0.4672	0.6540	0.110*
H3'B	0.6155	0.5204	0.5154	0.110*
H3'C	0.7364	0.6294	0.6100	0.110*
C4	0.78783 (15)	0.4906 (3)	0.40273 (15)	0.0485 (4)
H4A	0.7272	0.5990	0.3994	0.058*
C5	0.85135 (16)	0.4937 (3)	0.31609 (15)	0.0477 (4)
H5A	0.8320	0.6045	0.2571	0.057*
C6	0.93910 (15)	0.3381 (2)	0.31856 (13)	0.0415 (4)
O6	1.00633 (11)	0.32670 (18)	0.24022 (10)	0.0551 (4)
C6'	0.9926 (2)	0.5070 (3)	0.15832 (18)	0.0722 (6)
H6'A	1.0438	0.4802	0.1086	0.108*
H6'B	1.0197	0.6425	0.2033	0.108*
H6'C	0.9048	0.5203	0.1077	0.108*
C7	0.97036 (14)	0.1643 (2)	0.40879 (13)	0.0369 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0413 (8)	0.0408 (8)	0.0347 (8)	−0.0050 (7)	0.0135 (6)	−0.0012 (6)
C2	0.0368 (8)	0.0358 (8)	0.0354 (8)	−0.0044 (6)	0.0079 (6)	−0.0018 (6)
C3	0.0399 (8)	0.0430 (9)	0.0418 (9)	−0.0025 (7)	0.0106 (7)	−0.0049 (7)
O3	0.0601 (8)	0.0581 (8)	0.0593 (8)	0.0124 (6)	0.0302 (6)	0.0023 (6)
C3'	0.0627 (13)	0.0778 (14)	0.0891 (15)	0.0194 (10)	0.0387 (11)	−0.0018 (11)
C4	0.0454 (9)	0.0423 (9)	0.0515 (10)	0.0081 (7)	0.0083 (8)	0.0007 (8)
C5	0.0524 (10)	0.0401 (9)	0.0430 (9)	0.0014 (7)	0.0067 (7)	0.0087 (7)
C6	0.0442 (9)	0.0418 (9)	0.0344 (8)	−0.0064 (7)	0.0079 (7)	0.0029 (7)
O6	0.0641 (8)	0.0575 (8)	0.0474 (7)	0.0045 (6)	0.0236 (6)	0.0171 (5)
C6'	0.0966 (16)	0.0706 (12)	0.0534 (11)	0.0009 (11)	0.0307 (11)	0.0245 (10)
C7	0.0376 (8)	0.0360 (8)	0.0324 (7)	−0.0062 (6)	0.0060 (6)	−0.0012 (6)

Geometric parameters (Å, º)

C1—C7^i	1.388 (2)	C4—C5	1.423 (2)
C1—C2	1.395 (2)	C5—C6	1.347 (2)
C2—C7	1.423 (2)	C6—O6	1.3717 (19)
C2—C3	1.438 (2)	C6—C7	1.440 (2)
C3—C4	1.351 (2)	O6—C6'	1.4191 (19)
C3—O3	1.3725 (19)	C7—C1^i	1.388 (2)
O3—C3'	1.418 (2)
C7^i—C1—C2	121.85 (13)	C6—C5—C4	120.80 (14)
C1—C2—C7	118.87 (13)	C5—C6—O6	125.51 (14)
C1—C2—C3	122.17 (14)	C5—C6—C7	120.65 (14)
C7—C2—C3	118.95 (13)	O6—C6—C7	113.84 (13)
C4—C3—O3	125.55 (14)	C6—O6—C6'	117.18 (14)
C4—C3—C2	120.31 (15)	C1^i—C7—C2	119.27 (13)
O3—C3—C2	114.15 (13)	C1^i—C7—C6	122.27 (14)
C3—O3—C3'	116.71 (14)	C2—C7—C6	118.44 (13)
C3—C4—C5	120.85 (14)

Symmetry code: (i) −x+2, −y, −z+1.