A polymorph of terephthalaldehyde

A new ortho­rhom­bic polymorph of terephthalaldehyde, C₈H₆O₂, with a melting point of 372 K, has been obtained by recrystallization from ethanol. At room temperature, the crystals transform into the well known monoclinic form, with a melting point of 389 K. The crystal structure of the monoclinic form involves C—H⋯O hydrogen bonds, but no such bonds are observed in the orthorhombic form. The molecule is planar.

Related literature

For the structure of the monoclinic polymorph, see: Britton (1998).

Experimental

Crystal data

• C₈H₆O₂

• M_r = 134.13

• Orthorhombic, P c a 2₁

• a = 12.8811 (5) Å

• b = 3.8933 (3) Å

• c = 13.3202 (9) Å

• V = 668.01 (7) ų

• Z = 4

• Mo Kα radiation

• μ = 0.10 mm⁻¹

• T = 295 (2) K

• 0.20 × 0.10 × 0.10 mm

Data collection

• Bruker SMART 4K CCD area-detector diffractometer

• Absorption correction: none

• 3959 measured reflections

• 653 independent reflections

• 563 reflections with I > 2σ(I)

• R_int = 0.030

Refinement

• R[F² > 2σ(F²)] = 0.042

• wR(F²) = 0.112

• S = 1.04

• 653 reflections

• 91 parameters

• 1 restraint

• H-atom parameters constrained

• Δρ_max = 0.16 e Å⁻³

• Δρ_min = −0.10 e Å⁻³

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; 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.

Supporting information

S1. Comment

Terephthalaldehyde, (I), is a simple aromatic compound used in organic synthesis. It is known as a white substance, slightly soluble in water, with a melting point of 389 K. To the best of our knowledge, the only packing information of (I) in the solid state comes from the work of Britton (Britton, 1998), who investigated the intermolecular C—H···O arrangement in the structure of terephthalaldehyde and the crystals suitable for diffraction were obtained by recrystallization from an acetone/ethyl ether mixture.

A new polymorphic form of (I) has been obtained serendipitously during cocrystallization of pyridine and terephthalaldehyde from ethanol (Fig. 1). Flat needles which precipitated first from the solution had a melting point of 372 K and were identified as a new polymorphic form of (I) by X-ray crystallography. At room temperature, the crystals transform into the well known monoclinic form, with a melting point of 389 K. The crystal structure of the monoclinic form involves C—H···O hydrogen bonds but no such bonds are observed in the orthorhombic form (Fig. 2).

Related literature

For a related structure, see: Britton (1998).

S2. Experimental

The title compound was purchased from Aldrich.

S3. Refinement

All H atoms were initially located in a difference Fourier map and then included with constrained bond lengths and isotropic displacement parameters: C—H=0.93Å and U_iso(H)=1.2U_eq(C) for H atoms.

Computing details

Data collection: SMART (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 50% probability displacement ellipsoids (arbitrary spheres for H atoms).
	Fig. 2. The packing of the molecules, viewed down the b axis.

terephthalaldehyde

Crystal data

C8H6O2	F(000) = 280
Mr = 134.13	Dx = 1.334 Mg m^−3
Orthorhombic, Pca21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2ac	Cell parameters from 1070 reflections
a = 12.8811 (5) Å	θ = 3.1–23.5°
b = 3.8933 (3) Å	µ = 0.10 mm^−1
c = 13.3202 (9) Å	T = 295 K
V = 668.01 (7) Å^3	Block, colorless
Z = 4	0.20 × 0.10 × 0.10 mm

Data collection

Bruker SMART 4K CCD area-detector diffractometer	563 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.030
Graphite monochromator	θmax = 25.5°, θmin = 3.1°
ϕ and ω scans	h = −15→12
3959 measured reflections	k = −4→4
653 independent reflections	l = −16→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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.112	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0755P)^2 + 0.0133P] where P = (Fo^2 + 2Fc^2)/3
653 reflections	(Δ/σ)max = 0.014
91 parameters	Δρmax = 0.16 e Å^−3
1 restraint	Δρmin = −0.10 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	0.8164 (2)	0.3463 (7)	0.2145 (2)	0.0509 (7)
C2	0.9236 (2)	0.3850 (7)	0.2147 (3)	0.0545 (7)
H2	0.9566	0.4847	0.1599	0.065*
C3	0.9315 (2)	0.1279 (7)	0.3776 (2)	0.0515 (7)
C4	0.8239 (2)	0.0894 (7)	0.3770 (3)	0.0547 (7)
H4	0.7907	−0.0106	0.4316	0.066*
C5	0.7668 (2)	0.1993 (6)	0.2955 (3)	0.0543 (7)
H5	0.6950	0.1744	0.2953	0.065*
C6	0.9805 (2)	0.2776 (7)	0.2951 (3)	0.0547 (6)
H6	1.0523	0.3040	0.2949	0.066*
C7	0.7563 (4)	0.4635 (8)	0.1269 (4)	0.0707 (10)
H7	0.7934	0.5547	0.0733	0.085*
C8	0.9916 (3)	0.0084 (8)	0.4657 (4)	0.0627 (9)
H8	0.9550	−0.0874	0.5190	0.075*
O1	0.6637 (2)	0.4514 (7)	0.1187 (3)	0.0930 (10)
O2	1.0834 (2)	0.0266 (7)	0.4731 (4)	0.0876 (9)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0535 (16)	0.0494 (14)	0.0498 (17)	0.0041 (11)	0.0057 (14)	−0.0068 (13)
C2	0.0564 (18)	0.0551 (15)	0.0520 (17)	0.0022 (13)	0.0123 (15)	0.0015 (15)
C3	0.0547 (16)	0.0509 (14)	0.0490 (17)	−0.0008 (12)	0.0064 (15)	−0.0078 (13)
C4	0.0593 (19)	0.0573 (14)	0.0476 (17)	−0.0067 (14)	0.0140 (16)	0.0002 (14)
C5	0.0463 (13)	0.0570 (14)	0.0595 (15)	−0.0016 (12)	0.0102 (17)	−0.0083 (14)
C6	0.0448 (13)	0.0582 (14)	0.0610 (15)	−0.0003 (12)	0.0043 (18)	−0.0008 (14)
C7	0.071 (2)	0.077 (2)	0.063 (3)	0.0121 (16)	−0.006 (2)	−0.0016 (18)
C8	0.067 (2)	0.0704 (19)	0.0508 (19)	0.0030 (13)	0.009 (2)	0.0003 (14)
O1	0.075 (2)	0.129 (2)	0.075 (2)	0.0162 (14)	−0.0158 (19)	−0.0026 (18)
O2	0.0617 (17)	0.125 (2)	0.0761 (19)	0.0064 (12)	−0.0077 (16)	0.0074 (15)

Geometric parameters (Å, º)

C1—C5	1.378 (4)	C4—C5	1.379 (5)
C1—C2	1.389 (4)	C4—H4	0.9300
C1—C7	1.473 (6)	C5—H5	0.9300
C2—C6	1.363 (5)	C6—H6	0.9300
C2—H2	0.9300	C7—O1	1.199 (5)
C3—C4	1.393 (4)	C7—H7	0.9300
C3—C6	1.395 (4)	C8—O2	1.188 (4)
C3—C8	1.482 (6)	C8—H8	0.9300
C5—C1—C2	120.2 (3)	C1—C5—C4	119.9 (3)
C5—C1—C7	120.4 (3)	C1—C5—H5	120.1
C2—C1—C7	119.4 (3)	C4—C5—H5	120.1
C6—C2—C1	120.2 (3)	C2—C6—C3	120.2 (2)
C6—C2—H2	119.9	C2—C6—H6	119.9
C1—C2—H2	119.9	C3—C6—H6	119.9
C4—C3—C6	119.4 (3)	O1—C7—C1	125.6 (5)
C4—C3—C8	119.4 (3)	O1—C7—H7	117.2
C6—C3—C8	121.2 (3)	C1—C7—H7	117.2
C5—C4—C3	120.1 (3)	O2—C8—C3	124.5 (4)
C5—C4—H4	120.0	O2—C8—H8	117.7
C3—C4—H4	120.0	C3—C8—H8	117.7
C5—C1—C2—C6	0.1 (4)	C1—C2—C6—C3	0.0 (4)
C7—C1—C2—C6	−179.9 (3)	C4—C3—C6—C2	0.0 (4)
C6—C3—C4—C5	−0.2 (4)	C8—C3—C6—C2	179.9 (3)
C8—C3—C4—C5	180.0 (3)	C5—C1—C7—O1	1.8 (5)
C2—C1—C5—C4	−0.2 (4)	C2—C1—C7—O1	−178.2 (3)
C7—C1—C5—C4	179.7 (3)	C4—C3—C8—O2	179.2 (3)
C3—C4—C5—C1	0.2 (4)	C6—C3—C8—O2	−0.6 (5)