organic compounds
(E)-3-(3,5-Dimethoxyphenyl)-1-(2-methoxyphenyl)prop-2-en-1-one
aDivision of Bioscience and Biotechnology, BMIC, Konkuk University, Seoul 143-701, Republic of Korea, and bDepartment of Applied Chemistry, Dongduk Women's University, Seoul 136-714, Republic of Korea
*Correspondence e-mail: dskoh@dongduk.ac.kr
In the title molecule, C18H18O4, the dihedral angle between the benzene rings is 52.52 (7)°. The C=C bond of the central enone group adopts a trans conformation. The relative conformation of the two double bonds in the enone group is s-transoid. In the crystal, molecules are linked by pairs of weak C—H⋯O hydrogen bonds, forming inversion dimers.
Related literature
For the synthesis and biological properties of chalcone derivatives, see: Shin et al. (2012); Hwang et al. (2011). For related structures, see: Fun et al. (2012); Lee et al. (2012); Prasath et al. (2010).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: SMART (Bruker, 2000); cell SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
Supporting information
10.1107/S1600536813006302/lh5589sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536813006302/lh5589Isup2.hkl
Supporting information file. DOI: 10.1107/S1600536813006302/lh5589Isup3.cml
To a solution of 3,5-dimethoxybenzaldehyde (415 mg, 2.5 mmol) in 30 ml of ethanol was added 2-methoxyacetophenone (300 mg, 2 mmol) and the temperature was adjusted to around 276 K in an ice-bath. To the cooled reaction mixture was added 2 ml of 50% aqueous KOH solution, and the reaction mixture was stirred at room temperature for 5 h. This mixture was poured into iced water (50 ml) was acidified (pH = 3) with 3 N HCl solution to give a precipitate. Filtration and washing with water afforded crude solid of the title compound (560 mg, 94%). Recrystallization of the solid in ethanol gave single crystals (mp: 353–355 K).
H atoms were placed in calculated positions and refined as riding with C—H = 0.95–0.98 Å, and Uiso(H) = 1.2 Ueq(C) or Uiso(H) = 1.5 Ueq(Cmethyl).
Data collection: SMART (Bruker, 2000); cell
SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C18H18O4 | F(000) = 632 |
Mr = 298.32 | Dx = 1.285 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 2539 reflections |
a = 12.0925 (18) Å | θ = 2.7–28.1° |
b = 8.4460 (12) Å | µ = 0.09 mm−1 |
c = 15.109 (2) Å | T = 200 K |
β = 92.340 (3)° | Block, colorless |
V = 1541.9 (4) Å3 | 0.24 × 0.14 × 0.10 mm |
Z = 4 |
Bruker SMART CCD diffractometer | 1544 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.053 |
Graphite monochromator | θmax = 28.5°, θmin = 1.7° |
ϕ and ω scans | h = −16→14 |
11328 measured reflections | k = −11→10 |
3865 independent reflections | l = −20→19 |
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)] = 0.043 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.132 | H-atom parameters constrained |
S = 0.81 | w = 1/[σ2(Fo2) + (0.0575P)2] where P = (Fo2 + 2Fc2)/3 |
3865 reflections | (Δ/σ)max < 0.001 |
202 parameters | Δρmax = 0.21 e Å−3 |
0 restraints | Δρmin = −0.27 e Å−3 |
C18H18O4 | V = 1541.9 (4) Å3 |
Mr = 298.32 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 12.0925 (18) Å | µ = 0.09 mm−1 |
b = 8.4460 (12) Å | T = 200 K |
c = 15.109 (2) Å | 0.24 × 0.14 × 0.10 mm |
β = 92.340 (3)° |
Bruker SMART CCD diffractometer | 1544 reflections with I > 2σ(I) |
11328 measured reflections | Rint = 0.053 |
3865 independent reflections |
R[F2 > 2σ(F2)] = 0.043 | 0 restraints |
wR(F2) = 0.132 | H-atom parameters constrained |
S = 0.81 | Δρmax = 0.21 e Å−3 |
3865 reflections | Δρmin = −0.27 e Å−3 |
202 parameters |
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 > 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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.40664 (18) | 0.2012 (2) | 0.41632 (14) | 0.0370 (5) | |
O1 | 0.35034 (13) | 0.11209 (19) | 0.46017 (11) | 0.0569 (5) | |
C2 | 0.52596 (18) | 0.2050 (2) | 0.43027 (13) | 0.0366 (5) | |
H2 | 0.5597 | 0.1242 | 0.4658 | 0.044* | |
C3 | 0.59125 (17) | 0.3144 (2) | 0.39646 (13) | 0.0359 (5) | |
H3 | 0.5557 | 0.3937 | 0.3609 | 0.043* | |
C4 | 0.71093 (17) | 0.3259 (2) | 0.40791 (14) | 0.0352 (5) | |
C5 | 0.77006 (18) | 0.2441 (2) | 0.47412 (14) | 0.0371 (5) | |
H5 | 0.7322 | 0.1807 | 0.5151 | 0.045* | |
C6 | 0.88426 (18) | 0.2553 (2) | 0.48006 (14) | 0.0378 (5) | |
O2 | 0.93429 (13) | 0.17546 (17) | 0.54903 (10) | 0.0498 (4) | |
C7 | 1.05199 (19) | 0.1787 (3) | 0.55712 (17) | 0.0562 (7) | |
H7A | 1.0827 | 0.1313 | 0.5043 | 0.084* | |
H7B | 1.0770 | 0.1186 | 0.6097 | 0.084* | |
H7C | 1.0773 | 0.2886 | 0.5630 | 0.084* | |
C8 | 0.94020 (17) | 0.3433 (2) | 0.41983 (14) | 0.0384 (5) | |
H8 | 1.0187 | 0.3496 | 0.4239 | 0.046* | |
C9 | 0.88069 (18) | 0.4234 (2) | 0.35258 (15) | 0.0379 (5) | |
O3 | 0.94471 (12) | 0.50354 (18) | 0.29569 (11) | 0.0518 (5) | |
C10 | 0.8906 (2) | 0.5865 (3) | 0.22476 (16) | 0.0587 (7) | |
H10A | 0.8456 | 0.5124 | 0.1887 | 0.088* | |
H10B | 0.9459 | 0.6359 | 0.1880 | 0.088* | |
H10C | 0.8427 | 0.6685 | 0.2485 | 0.088* | |
C11 | 0.76750 (17) | 0.4184 (2) | 0.34780 (14) | 0.0359 (5) | |
H11 | 0.7275 | 0.4778 | 0.3037 | 0.043* | |
C12 | 0.34924 (17) | 0.3117 (2) | 0.35221 (13) | 0.0341 (5) | |
C13 | 0.26908 (18) | 0.4123 (2) | 0.38312 (14) | 0.0392 (5) | |
H13 | 0.2521 | 0.4093 | 0.4439 | 0.047* | |
C14 | 0.21334 (18) | 0.5168 (2) | 0.32693 (15) | 0.0427 (6) | |
H14 | 0.1595 | 0.5868 | 0.3490 | 0.051* | |
C15 | 0.23697 (18) | 0.5181 (2) | 0.23841 (15) | 0.0426 (6) | |
H15 | 0.1986 | 0.5893 | 0.1994 | 0.051* | |
C16 | 0.31528 (18) | 0.4178 (2) | 0.20554 (14) | 0.0399 (6) | |
H16 | 0.3303 | 0.4193 | 0.1443 | 0.048* | |
C17 | 0.37188 (17) | 0.3148 (2) | 0.26260 (14) | 0.0351 (5) | |
O4 | 0.44767 (12) | 0.20606 (17) | 0.23581 (9) | 0.0440 (4) | |
C18 | 0.4977 (2) | 0.2339 (3) | 0.15387 (16) | 0.0613 (8) | |
H18A | 0.4430 | 0.2171 | 0.1051 | 0.092* | |
H18B | 0.5597 | 0.1605 | 0.1477 | 0.092* | |
H18C | 0.5249 | 0.3431 | 0.1522 | 0.092* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0341 (13) | 0.0409 (13) | 0.0364 (12) | −0.0028 (10) | 0.0042 (10) | 0.0045 (10) |
O1 | 0.0405 (10) | 0.0666 (11) | 0.0637 (11) | −0.0077 (8) | 0.0019 (8) | 0.0290 (9) |
C2 | 0.0336 (13) | 0.0404 (13) | 0.0357 (12) | 0.0040 (10) | 0.0005 (10) | 0.0056 (10) |
C3 | 0.0343 (13) | 0.0366 (12) | 0.0369 (12) | 0.0016 (9) | 0.0009 (10) | 0.0009 (10) |
C4 | 0.0357 (13) | 0.0331 (11) | 0.0371 (12) | 0.0008 (10) | 0.0051 (10) | −0.0023 (10) |
C5 | 0.0377 (14) | 0.0385 (12) | 0.0350 (12) | 0.0012 (10) | −0.0012 (10) | 0.0049 (10) |
C6 | 0.0405 (14) | 0.0335 (12) | 0.0388 (13) | 0.0078 (10) | −0.0064 (11) | 0.0005 (10) |
O2 | 0.0446 (10) | 0.0522 (10) | 0.0517 (10) | 0.0050 (8) | −0.0108 (8) | 0.0071 (8) |
C7 | 0.0429 (16) | 0.0523 (15) | 0.0717 (18) | 0.0036 (12) | −0.0198 (13) | 0.0017 (13) |
C8 | 0.0283 (12) | 0.0369 (12) | 0.0497 (14) | 0.0034 (10) | −0.0019 (10) | −0.0016 (11) |
C9 | 0.0355 (13) | 0.0327 (12) | 0.0460 (14) | −0.0014 (10) | 0.0087 (11) | 0.0003 (10) |
O3 | 0.0360 (10) | 0.0558 (10) | 0.0642 (11) | 0.0011 (8) | 0.0085 (8) | 0.0177 (9) |
C10 | 0.0510 (17) | 0.0658 (17) | 0.0600 (17) | 0.0020 (13) | 0.0098 (14) | 0.0228 (14) |
C11 | 0.0307 (13) | 0.0341 (12) | 0.0428 (13) | 0.0019 (9) | 0.0014 (10) | 0.0018 (10) |
C12 | 0.0317 (12) | 0.0335 (11) | 0.0374 (12) | −0.0039 (9) | 0.0030 (10) | 0.0025 (10) |
C13 | 0.0375 (13) | 0.0433 (13) | 0.0370 (12) | −0.0041 (10) | 0.0044 (10) | 0.0006 (11) |
C14 | 0.0348 (13) | 0.0378 (13) | 0.0555 (16) | 0.0000 (10) | 0.0036 (11) | −0.0028 (12) |
C15 | 0.0350 (13) | 0.0393 (13) | 0.0530 (15) | −0.0023 (10) | −0.0050 (11) | 0.0091 (11) |
C16 | 0.0413 (14) | 0.0417 (13) | 0.0364 (13) | −0.0043 (11) | 0.0002 (11) | 0.0060 (11) |
C17 | 0.0318 (12) | 0.0348 (12) | 0.0389 (13) | −0.0020 (10) | 0.0040 (10) | −0.0005 (10) |
O4 | 0.0471 (10) | 0.0489 (9) | 0.0363 (9) | 0.0096 (7) | 0.0061 (7) | 0.0007 (7) |
C18 | 0.0630 (19) | 0.0699 (17) | 0.0529 (16) | 0.0118 (14) | 0.0248 (14) | 0.0074 (14) |
C1—O1 | 1.227 (2) | O3—C10 | 1.418 (3) |
C1—C2 | 1.450 (3) | C10—H10A | 0.9800 |
C1—C12 | 1.496 (3) | C10—H10B | 0.9800 |
C2—C3 | 1.331 (3) | C10—H10C | 0.9800 |
C2—H2 | 0.9500 | C11—H11 | 0.9500 |
C3—C4 | 1.454 (3) | C12—C13 | 1.384 (3) |
C3—H3 | 0.9500 | C12—C17 | 1.392 (3) |
C4—C5 | 1.390 (3) | C13—C14 | 1.381 (3) |
C4—C11 | 1.398 (3) | C13—H13 | 0.9500 |
C5—C6 | 1.384 (3) | C14—C15 | 1.379 (3) |
C5—H5 | 0.9500 | C14—H14 | 0.9500 |
C6—O2 | 1.362 (2) | C15—C16 | 1.378 (3) |
C6—C8 | 1.374 (3) | C15—H15 | 0.9500 |
O2—C7 | 1.424 (3) | C16—C17 | 1.386 (3) |
C7—H7A | 0.9800 | C16—H16 | 0.9500 |
C7—H7B | 0.9800 | C17—O4 | 1.370 (2) |
C7—H7C | 0.9800 | O4—C18 | 1.420 (2) |
C8—C9 | 1.396 (3) | C18—H18A | 0.9800 |
C8—H8 | 0.9500 | C18—H18B | 0.9800 |
C9—O3 | 1.361 (2) | C18—H18C | 0.9800 |
C9—C11 | 1.368 (3) | ||
O1—C1—C2 | 120.4 (2) | O3—C10—H10B | 109.5 |
O1—C1—C12 | 118.7 (2) | H10A—C10—H10B | 109.5 |
C2—C1—C12 | 120.86 (18) | O3—C10—H10C | 109.5 |
C3—C2—C1 | 124.2 (2) | H10A—C10—H10C | 109.5 |
C3—C2—H2 | 117.9 | H10B—C10—H10C | 109.5 |
C1—C2—H2 | 117.9 | C9—C11—C4 | 119.8 (2) |
C2—C3—C4 | 127.2 (2) | C9—C11—H11 | 120.1 |
C2—C3—H3 | 116.4 | C4—C11—H11 | 120.1 |
C4—C3—H3 | 116.4 | C13—C12—C17 | 119.01 (19) |
C5—C4—C11 | 119.6 (2) | C13—C12—C1 | 118.51 (18) |
C5—C4—C3 | 122.21 (19) | C17—C12—C1 | 122.46 (18) |
C11—C4—C3 | 118.11 (19) | C14—C13—C12 | 121.0 (2) |
C6—C5—C4 | 119.7 (2) | C14—C13—H13 | 119.5 |
C6—C5—H5 | 120.1 | C12—C13—H13 | 119.5 |
C4—C5—H5 | 120.1 | C15—C14—C13 | 119.1 (2) |
O2—C6—C8 | 124.0 (2) | C15—C14—H14 | 120.5 |
O2—C6—C5 | 115.25 (19) | C13—C14—H14 | 120.5 |
C8—C6—C5 | 120.7 (2) | C16—C15—C14 | 121.1 (2) |
C6—O2—C7 | 117.86 (18) | C16—C15—H15 | 119.4 |
O2—C7—H7A | 109.5 | C14—C15—H15 | 119.4 |
O2—C7—H7B | 109.5 | C15—C16—C17 | 119.4 (2) |
H7A—C7—H7B | 109.5 | C15—C16—H16 | 120.3 |
O2—C7—H7C | 109.5 | C17—C16—H16 | 120.3 |
H7A—C7—H7C | 109.5 | O4—C17—C16 | 123.80 (18) |
H7B—C7—H7C | 109.5 | O4—C17—C12 | 115.80 (18) |
C6—C8—C9 | 119.4 (2) | C16—C17—C12 | 120.32 (19) |
C6—C8—H8 | 120.3 | C17—O4—C18 | 117.45 (17) |
C9—C8—H8 | 120.3 | O4—C18—H18A | 109.5 |
O3—C9—C11 | 125.1 (2) | O4—C18—H18B | 109.5 |
O3—C9—C8 | 114.3 (2) | H18A—C18—H18B | 109.5 |
C11—C9—C8 | 120.6 (2) | O4—C18—H18C | 109.5 |
C9—O3—C10 | 117.80 (18) | H18A—C18—H18C | 109.5 |
O3—C10—H10A | 109.5 | H18B—C18—H18C | 109.5 |
O1—C1—C2—C3 | −168.7 (2) | C5—C4—C11—C9 | 2.3 (3) |
C12—C1—C2—C3 | 7.7 (3) | C3—C4—C11—C9 | −175.44 (19) |
C1—C2—C3—C4 | 179.76 (19) | O1—C1—C12—C13 | 54.6 (3) |
C2—C3—C4—C5 | −16.2 (3) | C2—C1—C12—C13 | −121.9 (2) |
C2—C3—C4—C11 | 161.5 (2) | O1—C1—C12—C17 | −124.0 (2) |
C11—C4—C5—C6 | 0.2 (3) | C2—C1—C12—C17 | 59.4 (3) |
C3—C4—C5—C6 | 177.85 (19) | C17—C12—C13—C14 | −1.3 (3) |
C4—C5—C6—O2 | 177.74 (18) | C1—C12—C13—C14 | −180.0 (2) |
C4—C5—C6—C8 | −1.7 (3) | C12—C13—C14—C15 | 1.2 (3) |
C8—C6—O2—C7 | −2.4 (3) | C13—C14—C15—C16 | −0.3 (3) |
C5—C6—O2—C7 | 178.19 (18) | C14—C15—C16—C17 | −0.5 (3) |
O2—C6—C8—C9 | −178.67 (19) | C15—C16—C17—O4 | 177.12 (19) |
C5—C6—C8—C9 | 0.7 (3) | C15—C16—C17—C12 | 0.5 (3) |
C6—C8—C9—O3 | −178.56 (18) | C13—C12—C17—O4 | −176.49 (17) |
C6—C8—C9—C11 | 1.9 (3) | C1—C12—C17—O4 | 2.1 (3) |
C11—C9—O3—C10 | −1.2 (3) | C13—C12—C17—C16 | 0.4 (3) |
C8—C9—O3—C10 | 179.24 (19) | C1—C12—C17—C16 | 179.03 (19) |
O3—C9—C11—C4 | 177.11 (18) | C16—C17—O4—C18 | 21.6 (3) |
C8—C9—C11—C4 | −3.4 (3) | C12—C17—O4—C18 | −161.6 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
C2—H2···O1i | 0.95 | 2.51 | 3.457 (3) | 172 |
Symmetry code: (i) −x+1, −y, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C18H18O4 |
Mr | 298.32 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 200 |
a, b, c (Å) | 12.0925 (18), 8.4460 (12), 15.109 (2) |
β (°) | 92.340 (3) |
V (Å3) | 1541.9 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.24 × 0.14 × 0.10 |
Data collection | |
Diffractometer | Bruker SMART CCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 11328, 3865, 1544 |
Rint | 0.053 |
(sin θ/λ)max (Å−1) | 0.670 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.043, 0.132, 0.81 |
No. of reflections | 3865 |
No. of parameters | 202 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.21, −0.27 |
Computer programs: SMART (Bruker, 2000), SAINT (Bruker, 2000), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
C2—H2···O1i | 0.95 | 2.51 | 3.457 (3) | 171.8 |
Symmetry code: (i) −x+1, −y, −z+1. |
References
Bruker (2000). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Fun, H.-K., Chia, T. S., Samshuddin, S., Narayana, B. & Sarojini, B. K. (2012). Acta Cryst. E68, o1560–o1561. CSD CrossRef IUCr Journals Google Scholar
Hwang, D., Hyun, J., Jo, G., Koh, D. & Lim, Y. (2011). Magn. Reson. Chem. 49, 41–45. Web of Science CrossRef CAS PubMed Google Scholar
Lee, H.-J., Lim, Y. & Koh, D. (2012). Acta Cryst. E68, o3403. CSD CrossRef IUCr Journals Google Scholar
Prasath, R., Sarveswari, S., Vijayakumar, V., Narasimhamurthy, T. & Tiekink, E. R. T. (2010). Acta Cryst. E66, o1110. Web of Science CSD CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Shin, S. Y., Ahn, S., Park, M. J., Yoon, H., Kim, M., Ji, S. Y., Koh, D., Lee, Y. H. & Lim, Y. (2012). J. Korean Soc. Appl. Biol. Chem. 55, 669–675. Web of Science CrossRef CAS Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
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Chalcones have an α,β-unsaturated carbonyl (enone) group which connects two aromatic rings at the 1,3-positions. Typically, the conformation of enone system is s-cisoid, in which the C═C and C═O double bonds are cis with respect to each other. Few examples of s-transoid conformations have been reported in the literature (Fun et al., 2012; Prasath et al., 2010). As a part of our studies on the substituent effects of chalcones on structures and biological activities (Shin et al., 2012; Hwang et al., 2011), the crystal structure of title compound has been determined.
The molecular structure of the title compound is shown in Fig. 1. The relative conformation of two double bonds of the central enone group is s-transoid. The trans configuration at the C1═C2 bond is reflected in the O1-C1-C2-C3 torsion angle of -168.7 (2)° compared to the value of -1.1 (5)° in a structure with an s-cisoid configuration (Lee et al., 2012). The dihedral angle between the benzene rings is 52.52 (7)°. Two methoxy groups at meta positions of the C4-C6/C8/C9/C11 ring are essentially co-planar with the ring [C8—C6—O2—C7 = -2.4 (3)° and C11—C9—O3—C10 = -1.2 (3)°]. However, the methoxy group at the ortho position of the C12-C17 ring is slightly twisted with respect to the benzene ring [C16—C17—O4—C18 = 21.6 (3)°]. In the crystal, molecules are linked by a pair of weak C—H···O hydrogen bonds to form inversion dimers (Table 1, Fig. 2).