(1E,3E)-1,4-Bis(4-meth­oxy­phen­yl)buta-1,3-diene

The title compound, C₁₈H₁₈O₂, which exhibits blue emission in the solid state, is an inter­mediate in the preparation of liquid crystals and polymers. The mol­ecule is located on an inversion centre. In the crystal, mol­ecules are arranged in a herringbone motif.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.045
• wR factor = 0.110
• Data-to-parameter ratio = 18.0

checkCIF/PLATON results

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Alert level G
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   0 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Although the crystal structures of a number of butadiene molecules have been reported (George et al., 1998; Vishnumurthy et al., 2002; Davis et al., 2004, 2008; Kumar et al., 2009; Ono et al., 2009), that of the title compound, C₁₈H₁₈O₂, (I), has not been determined and the structure is reported here (Fig. 1). There are four molecules of (I) per unit cell. The symmetrical molecules are arranged in a herringbone fashion (Koren et al., 2003) in which the molecules are packed in an edge-to-face orientation (Fig. 2).

Thermal properties: On heating, crystals of (I) melted at 237 °C, which on further heating sublimed at 246 °C. The sublimed-condensed crystals were chemically unaltered as evidenced by NMR and MS analyses.

Related literature

For related structures, see: George et al. (1998); Vishnumurthy et al. (2002); Davis et al. (2004, 2008); Kumar et al. (2009); Ono et al. (2009). For the synthesis and the use of the title compound in the preparation of polymers and chiral liquid crystals, see: Rotarski (1908); Wang et al. (2003); Das et al. (2008). For molecules with a herringbone arrangement, see: Koren et al. (2003).

S2. Experimental

A mixture of diethyl-4-methoxybenzylphosphonate (1 equiv) and potassium tert-butoxide (5 equiv) were stirred in dry DMF at room temperature and cooled to 273 K. 4-Methoxycinnamaldehyde (1 equiv) dissolved in dry DMF was slowly added into the solution. The reaction mixture was allowed to stir for 12 h at room temperature. TLC analysis indicated completion of reaction. Reaction mixture was poured into ice water, extracted with dichloromethane and concentrated under reduced pressure. The residue was washed with ethyl acetate and filtered. The compound being insoluble in ethyl acetate remained in the residue. This was repeatedly washed with ethyl acetate (small quantities) to obtain pure title compound. The small amount of compound which remained in the filtrate was recovered by column chromatography through silica gel (100–200 mesh), using 5% ethyl acetate/hexane as the mobile phase. Single crystals obtained from ethylacetate at room temperature were of poor quality (high R value) and the structure determination was carried out at 100 K. Fresh crystals were grown from chloroform/hexanes at room temperature which were of higher quality to permit X-ray analysis at 293 K. The data presented herein are from the latter determination.

S3. Refinement

H atoms bonded to N and O atoms were located in a difference map and refined with distance restraints of O—H = 0.84 (2) and N—H = 0.87 (2) Å, and with U_iso(H) = 1.2U_eq(N,O). Other H atoms were positioned geometrically and refined using a riding model (including free rotation about the ethanol C—C bond), with C—H = 0.95–0.99 Å and with U_iso(H) = 1.2 (1.5 for methyl groups) times U_eq(C).

Computing details

Data collection: APEX2 (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms.
	Fig. 2. The herringbone packing of (I) in the crystal structure.

(1E,3E)-1,4-Bis(4-methoxyphenyl)buta-1,3-diene

Crystal data

C18H18O2	F(000) = 568
Mr = 266.32	Dx = 1.224 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 7512 reflections
a = 7.3543 (3) Å	θ = 2.6–23.6°
b = 6.2617 (3) Å	µ = 0.08 mm^−1
c = 31.3872 (13) Å	T = 293 K
V = 1445.39 (11) Å^3	Pyramidal, colourless
Z = 4	0.25 × 0.22 × 0.22 mm

Data collection

Bruker X8 APEXII CCD area-detector diffractometer	1658 independent reflections
Radiation source: fine-focus sealed tube	1287 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
ϕ and ω scans	θmax = 27.5°, θmin = 1.3°
Absorption correction: numerical (SADABS; Sheldrick, 2006)	h = −8→9
Tmin = 0.981, Tmax = 0.983	k = −8→8
40427 measured reflections	l = −40→37

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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.110	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0429P)^2 + 0.3178P] where P = (Fo^2 + 2Fc^2)/3
1658 reflections	(Δ/σ)max < 0.001
92 parameters	Δρmax = 0.13 e Å^−3
0 restraints	Δρmin = −0.13 e Å^−3

Special details

Experimental. 2010–02-01 # Formatted by publCIF

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
O1	−0.01884 (15)	0.42509 (16)	0.19955 (3)	0.0584 (3)
C1	−0.00667 (17)	0.4944 (2)	0.15818 (4)	0.0420 (3)
C2	0.07908 (18)	0.3855 (2)	0.12580 (4)	0.0458 (3)
H2	0.1341	0.2543	0.1310	0.055*
C3	0.08211 (18)	0.4740 (2)	0.08547 (4)	0.0441 (3)
H3	0.1386	0.3988	0.0636	0.053*
C4	0.00422 (16)	0.6707 (2)	0.07623 (4)	0.0396 (3)
C5	−0.08465 (17)	0.7752 (2)	0.10963 (4)	0.0440 (3)
H5	−0.1411	0.9056	0.1046	0.053*
C6	−0.09002 (18)	0.6884 (2)	0.14980 (4)	0.0455 (3)
H6	−0.1501	0.7605	0.1716	0.055*
C7	0.02594 (18)	0.7620 (2)	0.03382 (4)	0.0452 (3)
H7	0.0769	0.6729	0.0133	0.054*
C8	−0.01863 (18)	0.9584 (2)	0.02086 (4)	0.0461 (3)
H8	−0.0777	1.0472	0.0402	0.055*
C9	0.0738 (3)	0.2339 (3)	0.21039 (5)	0.0789 (6)
H9A	0.0254	0.1176	0.1940	0.118*
H9B	0.0577	0.2050	0.2402	0.118*
H9C	0.2010	0.2497	0.2043	0.118*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0773 (7)	0.0568 (6)	0.0410 (6)	0.0056 (6)	0.0018 (5)	0.0061 (5)
C1	0.0447 (7)	0.0442 (7)	0.0371 (7)	−0.0047 (6)	−0.0013 (5)	0.0012 (6)
C2	0.0485 (8)	0.0395 (7)	0.0495 (8)	0.0068 (6)	0.0004 (6)	0.0015 (6)
C3	0.0454 (7)	0.0431 (7)	0.0439 (7)	0.0041 (6)	0.0049 (6)	−0.0034 (6)
C4	0.0366 (6)	0.0405 (7)	0.0416 (7)	−0.0029 (5)	−0.0018 (5)	−0.0007 (5)
C5	0.0446 (7)	0.0395 (7)	0.0479 (8)	0.0056 (6)	0.0001 (6)	−0.0005 (6)
C6	0.0485 (8)	0.0439 (7)	0.0441 (7)	0.0043 (6)	0.0036 (6)	−0.0047 (6)
C7	0.0464 (7)	0.0484 (8)	0.0407 (7)	−0.0010 (6)	−0.0012 (6)	−0.0009 (6)
C8	0.0463 (7)	0.0488 (8)	0.0430 (7)	−0.0031 (6)	−0.0036 (6)	0.0015 (6)
C9	0.1102 (16)	0.0692 (11)	0.0574 (10)	0.0158 (11)	−0.0010 (10)	0.0204 (9)

Geometric parameters (Å, º)

O1—C1	1.3721 (15)	C5—C6	1.3735 (18)
O1—C9	1.4190 (19)	C5—H5	0.9300
C1—C2	1.3768 (18)	C6—H6	0.9300
C1—C6	1.3860 (18)	C7—C8	1.3367 (19)
C2—C3	1.3820 (18)	C7—H7	0.9300
C2—H2	0.9300	C8—C8^i	1.435 (3)
C3—C4	1.3890 (18)	C8—H8	0.9300
C3—H3	0.9300	C9—H9A	0.9600
C4—C5	1.3978 (18)	C9—H9B	0.9600
C4—C7	1.4573 (18)	C9—H9C	0.9600
C1—O1—C9	117.55 (12)	C5—C6—C1	120.54 (12)
O1—C1—C2	124.87 (12)	C5—C6—H6	119.7
O1—C1—C6	115.34 (12)	C1—C6—H6	119.7
C2—C1—C6	119.78 (12)	C8—C7—C4	127.73 (13)
C1—C2—C3	119.00 (12)	C8—C7—H7	116.1
C1—C2—H2	120.5	C4—C7—H7	116.1
C3—C2—H2	120.5	C7—C8—C8^i	124.37 (17)
C2—C3—C4	122.70 (12)	C7—C8—H8	117.8
C2—C3—H3	118.6	C8^i—C8—H8	117.8
C4—C3—H3	118.6	O1—C9—H9A	109.5
C3—C4—C5	116.82 (12)	O1—C9—H9B	109.5
C3—C4—C7	119.55 (12)	H9A—C9—H9B	109.5
C5—C4—C7	123.56 (12)	O1—C9—H9C	109.5
C6—C5—C4	121.12 (12)	H9A—C9—H9C	109.5
C6—C5—H5	119.4	H9B—C9—H9C	109.5
C4—C5—H5	119.4
C9—O1—C1—C2	4.3 (2)	C7—C4—C5—C6	−175.32 (12)
C9—O1—C1—C6	−176.19 (14)	C4—C5—C6—C1	0.1 (2)
O1—C1—C2—C3	−179.72 (12)	O1—C1—C6—C5	179.15 (12)
C6—C1—C2—C3	0.81 (19)	C2—C1—C6—C5	−1.33 (19)
C1—C2—C3—C4	0.9 (2)	C3—C4—C7—C8	−170.76 (13)
C2—C3—C4—C5	−2.09 (19)	C5—C4—C7—C8	6.0 (2)
C2—C3—C4—C7	174.90 (13)	C4—C7—C8—C8^i	175.49 (15)
C3—C4—C5—C6	1.54 (18)

Symmetry code: (i) −x, −y+2, −z.