organic compounds
(E)-2-[(4-Ethoxyphenyl)iminomethyl]-4-methoxyphenol
aDepartment of Physics, Ondokuz Mayıs University, TR-55139 Samsun, Turkey, and bFaculty of Education, Sinop University, Sinop, Turkey
*Correspondence e-mail: arzuozek@omu.edu.tr
In the molecule of the title compound, C16H17NO3, the aromatic rings are oriented at a dihedral angle of 29.25 (8)°. An intramolecular O—H⋯N hydrogen bond results in the formation of a nearly planar [maximum deviation 0.034 (13) Å] six-membered ring, which is oriented at dihedral angles of 0.91 (1) and 28.91 (12)° with respect to the aromatic rings. The title molecule is a phenol–imine tautomer, as evidenced by C—O, C—N and C—C bond lengths. In the crystal, molecules are linked by intermolecular C—H⋯O hydrogen bonds that generate C(8) chains.
Related literature
For background to this study, see: Özek et al., 2007. For related structures, see: Özek et al. (2009); Özek et al. (2008).
Experimental
Crystal data
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Refinement
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Data collection: X-AREA (Stoe & Cie, 2002); cell X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
Supporting information
https://doi.org/10.1107/S1600536809040586/ez2189sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536809040586/ez2189Isup2.hkl
The compound (E)-2-[(4-ethoxyphenylimino)methyl]-4-methoxyphenol was prepared by refluxing a mixture of a solution containing 5-methoxysalicylaldehyde (0.5 g, 3.3 mmol) in 20 ml ethanol and a solution containing 4-ethoxyaniline (0.45 g, 3.3 mmol) in 20 ml ethanol. The reaction mixture was stirred for 1 h under reflux. Crystals of (E)-2-[(4-ethoxyphenylimino)methyl]-4- methoxyphenol suitable for X-ray analysis were obtained from ethanol by slow evaporation (yield % 75; m.p. 365–367 K).
All the H-atoms were found in difference-density maps, and refined freely. The C—H bond lengths are 0.90 (3)–1.06 (2) Å.
The present work is part of a structural study of
(Özek et al., 2009; Özek et al., 2008; Özek et al., 2007) and we report here the structure of (E)-2-[(4-ethoxyphenylimino)methyl]-4-methoxyphenol, (I).In general, O-hydroxy
exhibit two possible tautomeric forms, the phenol-imine (or benzenoid) and keto-amine (or quinoid) forms. Depending on the tautomers, two types of intra-molecular hydrogen bonds are possible: O—H···N in benzenoid and N—H···O in quinoid tautomers. In the title compound the H atom is located on atom O1, thus the phenol-imine tautomer is favored over the keto-amine form, as indicated by the C2—O1, C8—N1, C1—C8 and C1—C2 bond lengths (Fig. 1 and Table 2). The O1—C2 bond length of 1.351 (2) Å indicates single-bond character, whereas the N1—C8 bond length of 1.277 (2) Å indicates a high degree of double-bond character. A similar result was observed in the X-ray crystal and computational structural study of (E)-2-[(2-chlorophenyl) iminomethyl]-4-methoxyphenol [C—O=1.357 (17) Å, C—N= 1.278 (17) Å, Özek et al., 2008.It is known that
may exhibit thermochromism or depending on the planarity or non-planarity of the molecule, respectively. Therefore, one can expect photochromic properties in (I) caused by non-planarity of the molecules; the dihedral angle between ring A (C1—C6) and ring B (C9—C14) is 29.25 (8) °. The intramolecular O—H···N hydrogen bond (Table 1) results in the formation of a nearly planar six-membered ring C (O1/H1/N1/C1/C2/C8), in which it is oriented with respect to rings A and B at dihedral angles of A/C= 0.91 (1) ° and B/C= 28.91 (12) °. It is thus coplanar with the adjacent ring A. It generates an S(6) ring motif. The O1···N1 distance of 2.5962 (18) Å is comparable to those observed for analogous hydrogen bonds in three (E)-2-[(bromophenyl)iminomethyl]-4-methoxyphenols [2.603 (2) Å, 2.638 (7) Å, 2.577 (4) Å; Özek et al., 2007]. In the weak intermolecular C—H···O hydrogen bonds (Table 1) result in the formation of C(8) chains along the c axis (Fig. 2), which may play a role in the stabilization of the structure.For background to this study, see: Özek et al., 2007. For related structures, see: Özek et al. (2009); Özek et al. (2008).
Data collection: X-AREA (Stoe & Cie, 2002); cell
X-AREA (Stoe & Cie, 2002); data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).C16H17NO3 | F(000) = 576 |
Mr = 271.31 | Dx = 1.276 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 14704 reflections |
a = 14.8558 (7) Å | θ = 2.0–28.0° |
b = 13.7669 (7) Å | µ = 0.09 mm−1 |
c = 6.9042 (3) Å | T = 296 K |
β = 90.287 (4)° | Prism, brown |
V = 1412.02 (11) Å3 | 0.77 × 0.51 × 0.28 mm |
Z = 4 |
Stoe IPDS II diffractometer | 2938 independent reflections |
Radiation source: fine-focus sealed tube | 2014 reflections with I > 2σ(I) |
Plane graphite monochromator | Rint = 0.051 |
Detector resolution: 6.67 pixels mm-1 | θmax = 26.5°, θmin = 2.0° |
ω scans | h = −18→18 |
Absorption correction: integration (X-RED32; Stoe & Cie, 2002) | k = −17→17 |
Tmin = 0.943, Tmax = 0.973 | l = −8→7 |
14704 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.044 | All H-atom parameters refined |
wR(F2) = 0.123 | w = 1/[σ2(Fo2) + (0.0671P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
2938 reflections | Δρmax = 0.11 e Å−3 |
250 parameters | Δρmin = −0.12 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0043 (13) |
C16H17NO3 | V = 1412.02 (11) Å3 |
Mr = 271.31 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 14.8558 (7) Å | µ = 0.09 mm−1 |
b = 13.7669 (7) Å | T = 296 K |
c = 6.9042 (3) Å | 0.77 × 0.51 × 0.28 mm |
β = 90.287 (4)° |
Stoe IPDS II diffractometer | 2938 independent reflections |
Absorption correction: integration (X-RED32; Stoe & Cie, 2002) | 2014 reflections with I > 2σ(I) |
Tmin = 0.943, Tmax = 0.973 | Rint = 0.051 |
14704 measured reflections |
R[F2 > 2σ(F2)] = 0.044 | 0 restraints |
wR(F2) = 0.123 | All H-atom parameters refined |
S = 1.04 | Δρmax = 0.11 e Å−3 |
2938 reflections | Δρmin = −0.12 e Å−3 |
250 parameters |
Experimental. 260 frames, detector distance = 100 mm |
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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.67303 (10) | 0.38075 (10) | 0.1954 (2) | 0.0592 (4) | |
C2 | 0.66776 (11) | 0.36315 (11) | −0.0041 (2) | 0.0644 (4) | |
C3 | 0.74627 (12) | 0.35280 (13) | −0.1091 (2) | 0.0738 (5) | |
C4 | 0.82841 (13) | 0.35935 (13) | −0.0201 (2) | 0.0743 (5) | |
C5 | 0.83522 (11) | 0.37538 (12) | 0.1785 (2) | 0.0677 (4) | |
C6 | 0.75803 (10) | 0.38680 (12) | 0.2840 (2) | 0.0633 (4) | |
C7 | 0.93120 (15) | 0.38888 (19) | 0.4548 (3) | 0.0868 (6) | |
C8 | 0.59256 (11) | 0.38970 (11) | 0.3128 (2) | 0.0635 (4) | |
C9 | 0.43564 (10) | 0.38370 (11) | 0.3529 (2) | 0.0587 (4) | |
C10 | 0.43263 (11) | 0.35185 (12) | 0.5428 (2) | 0.0663 (4) | |
C11 | 0.35242 (11) | 0.34958 (13) | 0.6444 (2) | 0.0669 (4) | |
C12 | 0.27310 (10) | 0.37865 (10) | 0.5544 (2) | 0.0593 (4) | |
C13 | 0.27591 (11) | 0.41068 (12) | 0.3634 (2) | 0.0658 (4) | |
C14 | 0.35554 (10) | 0.41219 (12) | 0.2639 (2) | 0.0647 (4) | |
C15 | 0.18545 (13) | 0.35600 (18) | 0.8412 (3) | 0.0808 (5) | |
C16 | 0.08889 (15) | 0.3588 (2) | 0.8994 (4) | 0.1001 (7) | |
N1 | 0.51409 (8) | 0.38318 (9) | 0.23737 (18) | 0.0634 (3) | |
O1 | 0.58802 (9) | 0.35510 (10) | −0.09793 (18) | 0.0830 (4) | |
O2 | 0.92111 (8) | 0.37741 (11) | 0.25288 (18) | 0.0904 (4) | |
O3 | 0.19015 (7) | 0.37712 (8) | 0.63865 (15) | 0.0709 (3) | |
H1 | 0.5439 (17) | 0.3668 (16) | −0.006 (3) | 0.116 (8)* | |
H3 | 0.7423 (13) | 0.3381 (14) | −0.243 (3) | 0.100 (6)* | |
H4 | 0.8816 (14) | 0.3471 (14) | −0.091 (3) | 0.093 (6)* | |
H6 | 0.7613 (11) | 0.3976 (13) | 0.421 (3) | 0.083 (5)* | |
H7A | 0.9038 (14) | 0.4477 (18) | 0.503 (3) | 0.105 (7)* | |
H7B | 0.8999 (13) | 0.3335 (15) | 0.528 (3) | 0.093 (6)* | |
H7C | 0.9976 (15) | 0.3864 (13) | 0.473 (3) | 0.096 (6)* | |
H8 | 0.6036 (11) | 0.4006 (12) | 0.449 (3) | 0.080 (5)* | |
H10 | 0.4858 (12) | 0.3266 (13) | 0.606 (2) | 0.082 (5)* | |
H11 | 0.3521 (11) | 0.3218 (13) | 0.777 (3) | 0.084 (5)* | |
H13 | 0.2221 (11) | 0.4322 (12) | 0.307 (2) | 0.073 (5)* | |
H14 | 0.3585 (10) | 0.4324 (13) | 0.130 (2) | 0.077 (5)* | |
H15A | 0.2218 (13) | 0.4035 (14) | 0.913 (3) | 0.090 (6)* | |
H15B | 0.2105 (13) | 0.2887 (16) | 0.862 (3) | 0.112 (7)* | |
H16A | 0.0524 (19) | 0.304 (2) | 0.825 (4) | 0.158 (11)* | |
H16B | 0.0618 (16) | 0.4162 (19) | 0.873 (4) | 0.128 (9)* | |
H16C | 0.0829 (14) | 0.3476 (15) | 1.038 (4) | 0.105 (7)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0603 (8) | 0.0579 (8) | 0.0594 (8) | 0.0004 (6) | 0.0039 (6) | −0.0015 (6) |
C2 | 0.0680 (9) | 0.0663 (10) | 0.0589 (8) | −0.0002 (7) | −0.0019 (7) | 0.0026 (7) |
C3 | 0.0824 (12) | 0.0850 (12) | 0.0542 (9) | 0.0049 (8) | 0.0085 (8) | 0.0022 (8) |
C4 | 0.0714 (11) | 0.0849 (12) | 0.0666 (10) | 0.0082 (8) | 0.0157 (8) | 0.0059 (8) |
C5 | 0.0598 (9) | 0.0752 (10) | 0.0682 (9) | 0.0016 (7) | 0.0055 (7) | 0.0066 (7) |
C6 | 0.0619 (9) | 0.0718 (10) | 0.0561 (8) | −0.0011 (7) | 0.0043 (7) | −0.0025 (7) |
C7 | 0.0665 (12) | 0.1075 (17) | 0.0864 (13) | −0.0070 (11) | −0.0097 (9) | −0.0061 (12) |
C8 | 0.0634 (9) | 0.0665 (10) | 0.0605 (9) | 0.0000 (7) | 0.0005 (7) | −0.0065 (7) |
C9 | 0.0577 (8) | 0.0580 (8) | 0.0604 (8) | 0.0005 (6) | −0.0006 (6) | −0.0042 (6) |
C10 | 0.0574 (8) | 0.0769 (10) | 0.0645 (9) | 0.0066 (7) | −0.0065 (7) | 0.0038 (7) |
C11 | 0.0627 (9) | 0.0768 (10) | 0.0610 (9) | 0.0051 (7) | −0.0026 (7) | 0.0078 (8) |
C12 | 0.0546 (8) | 0.0601 (9) | 0.0633 (8) | 0.0009 (6) | 0.0002 (6) | −0.0028 (7) |
C13 | 0.0580 (9) | 0.0769 (10) | 0.0625 (9) | 0.0070 (7) | −0.0078 (7) | 0.0016 (7) |
C14 | 0.0651 (9) | 0.0737 (10) | 0.0554 (8) | 0.0031 (7) | −0.0026 (7) | 0.0020 (7) |
C15 | 0.0702 (11) | 0.1014 (15) | 0.0707 (11) | 0.0031 (10) | 0.0062 (8) | 0.0190 (10) |
C16 | 0.0712 (13) | 0.139 (2) | 0.0902 (15) | 0.0020 (13) | 0.0187 (11) | 0.0247 (15) |
N1 | 0.0595 (8) | 0.0655 (8) | 0.0651 (7) | −0.0001 (6) | 0.0016 (6) | −0.0029 (6) |
O1 | 0.0742 (8) | 0.1130 (10) | 0.0616 (7) | −0.0007 (6) | −0.0088 (6) | −0.0047 (6) |
O2 | 0.0576 (7) | 0.1344 (12) | 0.0794 (8) | 0.0014 (6) | 0.0047 (6) | 0.0062 (7) |
O3 | 0.0564 (6) | 0.0901 (8) | 0.0661 (6) | 0.0021 (5) | 0.0011 (5) | 0.0055 (5) |
C1—C2 | 1.401 (2) | C9—C14 | 1.393 (2) |
C1—C6 | 1.403 (2) | C9—N1 | 1.4154 (19) |
C1—C8 | 1.453 (2) | C10—C11 | 1.386 (2) |
C2—O1 | 1.3518 (19) | C10—H10 | 0.965 (18) |
C2—C3 | 1.384 (2) | C11—C12 | 1.388 (2) |
C3—C4 | 1.367 (3) | C11—H11 | 0.990 (17) |
C3—H3 | 0.94 (2) | C12—O3 | 1.3653 (18) |
C4—C5 | 1.392 (2) | C12—C13 | 1.392 (2) |
C4—H4 | 0.95 (2) | C13—C14 | 1.371 (2) |
C5—C6 | 1.371 (2) | C13—H13 | 0.936 (17) |
C5—O2 | 1.373 (2) | C14—H14 | 0.966 (17) |
C6—H6 | 0.957 (18) | C15—O3 | 1.431 (2) |
C7—O2 | 1.410 (2) | C15—C16 | 1.492 (3) |
C7—H7A | 0.97 (2) | C15—H15A | 0.98 (2) |
C7—H7B | 1.03 (2) | C15—H15B | 1.01 (2) |
C7—H7C | 0.99 (2) | C16—H16A | 1.06 (3) |
C8—N1 | 1.277 (2) | C16—H16B | 0.90 (3) |
C8—H8 | 0.963 (18) | C16—H16C | 0.98 (2) |
C9—C10 | 1.384 (2) | O1—H1 | 0.93 (3) |
C2—C1—C6 | 119.01 (14) | C9—C10—H10 | 120.8 (10) |
C2—C1—C8 | 121.41 (14) | C11—C10—H10 | 117.9 (10) |
C6—C1—C8 | 119.55 (13) | C10—C11—C12 | 119.84 (15) |
O1—C2—C3 | 118.65 (14) | C10—C11—H11 | 118.9 (10) |
O1—C2—C1 | 122.00 (14) | C12—C11—H11 | 121.1 (10) |
C3—C2—C1 | 119.35 (15) | O3—C12—C11 | 124.83 (14) |
C4—C3—C2 | 120.70 (16) | O3—C12—C13 | 116.10 (13) |
C4—C3—H3 | 120.3 (12) | C11—C12—C13 | 119.06 (14) |
C2—C3—H3 | 119.0 (12) | C14—C13—C12 | 120.63 (15) |
C3—C4—C5 | 120.92 (16) | C14—C13—H13 | 121.6 (10) |
C3—C4—H4 | 120.2 (12) | C12—C13—H13 | 117.7 (10) |
C5—C4—H4 | 118.7 (12) | C13—C14—C9 | 120.83 (15) |
C6—C5—O2 | 125.23 (15) | C13—C14—H14 | 121.8 (9) |
C6—C5—C4 | 119.02 (16) | C9—C14—H14 | 117.4 (9) |
O2—C5—C4 | 115.75 (14) | O3—C15—C16 | 108.04 (16) |
C5—C6—C1 | 120.99 (15) | O3—C15—H15A | 109.3 (11) |
C5—C6—H6 | 120.3 (10) | C16—C15—H15A | 111.9 (11) |
C1—C6—H6 | 118.7 (10) | O3—C15—H15B | 107.7 (12) |
O2—C7—H7A | 113.0 (12) | C16—C15—H15B | 109.9 (12) |
O2—C7—H7B | 110.8 (11) | H15A—C15—H15B | 109.9 (17) |
H7A—C7—H7B | 105.2 (17) | C15—C16—H16A | 109.9 (15) |
O2—C7—H7C | 103.0 (11) | C15—C16—H16B | 113.3 (16) |
H7A—C7—H7C | 113.8 (16) | H16A—C16—H16B | 107 (2) |
H7B—C7—H7C | 111.3 (15) | C15—C16—H16C | 110.6 (13) |
N1—C8—C1 | 121.24 (14) | H16A—C16—H16C | 108 (2) |
N1—C8—H8 | 123.9 (10) | H16B—C16—H16C | 107 (2) |
C1—C8—H8 | 114.9 (10) | C8—N1—C9 | 121.49 (13) |
C10—C9—C14 | 118.40 (14) | C2—O1—H1 | 106.1 (14) |
C10—C9—N1 | 124.26 (13) | C5—O2—C7 | 117.78 (14) |
C14—C9—N1 | 117.20 (13) | C12—O3—C15 | 117.91 (12) |
C9—C10—C11 | 121.23 (14) | ||
C6—C1—C2—O1 | 179.03 (14) | C9—C10—C11—C12 | 0.7 (3) |
C8—C1—C2—O1 | 1.0 (2) | C10—C11—C12—O3 | 178.28 (15) |
C6—C1—C2—C3 | −0.4 (2) | C10—C11—C12—C13 | −0.7 (2) |
C8—C1—C2—C3 | −178.42 (15) | O3—C12—C13—C14 | −178.05 (15) |
O1—C2—C3—C4 | −179.32 (15) | C11—C12—C13—C14 | 1.0 (2) |
C1—C2—C3—C4 | 0.2 (3) | C12—C13—C14—C9 | −1.3 (3) |
C2—C3—C4—C5 | 0.8 (3) | C10—C9—C14—C13 | 1.3 (2) |
C3—C4—C5—C6 | −1.5 (3) | N1—C9—C14—C13 | 177.16 (14) |
C3—C4—C5—O2 | 177.91 (16) | C1—C8—N1—C9 | 174.64 (13) |
O2—C5—C6—C1 | −178.13 (15) | C10—C9—N1—C8 | −27.7 (2) |
C4—C5—C6—C1 | 1.2 (2) | C14—C9—N1—C8 | 156.79 (15) |
C2—C1—C6—C5 | −0.3 (2) | C6—C5—O2—C7 | 2.3 (3) |
C8—C1—C6—C5 | 177.78 (14) | C4—C5—O2—C7 | −177.08 (18) |
C2—C1—C8—N1 | −1.0 (2) | C11—C12—O3—C15 | 8.4 (2) |
C6—C1—C8—N1 | −179.00 (14) | C13—C12—O3—C15 | −172.62 (16) |
C14—C9—C10—C11 | −1.0 (2) | C16—C15—O3—C12 | 179.78 (18) |
N1—C9—C10—C11 | −176.53 (15) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···N1 | 0.93 (3) | 1.75 (3) | 2.5962 (18) | 149 (2) |
C10—H10···O1i | 0.965 (18) | 2.571 (18) | 3.3801 (19) | 141.5 (13) |
Symmetry code: (i) x, y, z+1. |
Experimental details
Crystal data | |
Chemical formula | C16H17NO3 |
Mr | 271.31 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 296 |
a, b, c (Å) | 14.8558 (7), 13.7669 (7), 6.9042 (3) |
β (°) | 90.287 (4) |
V (Å3) | 1412.02 (11) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.77 × 0.51 × 0.28 |
Data collection | |
Diffractometer | Stoe IPDS II |
Absorption correction | Integration (X-RED32; Stoe & Cie, 2002) |
Tmin, Tmax | 0.943, 0.973 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 14704, 2938, 2014 |
Rint | 0.051 |
(sin θ/λ)max (Å−1) | 0.628 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.044, 0.123, 1.04 |
No. of reflections | 2938 |
No. of parameters | 250 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.11, −0.12 |
Computer programs: X-AREA (Stoe & Cie, 2002), X-RED32 (Stoe & Cie, 2002), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999).
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···N1 | 0.93 (3) | 1.75 (3) | 2.5962 (18) | 149 (2) |
C10—H10···O1i | 0.965 (18) | 2.571 (18) | 3.3801 (19) | 141.5 (13) |
Symmetry code: (i) x, y, z+1. |
Acknowledgements
The authors acknowledge the Faculty of Arts and Sciences, Ondokuz Mayıs University, Turkey, for the use of the Stoe IPDS II diffractometer (purchased under grant F.279 of the University Research Fund).
References
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The present work is part of a structural study of Schiff bases (Özek et al., 2009; Özek et al., 2008; Özek et al., 2007) and we report here the structure of (E)-2-[(4-ethoxyphenylimino)methyl]-4-methoxyphenol, (I).
In general, O-hydroxy Schiff bases exhibit two possible tautomeric forms, the phenol-imine (or benzenoid) and keto-amine (or quinoid) forms. Depending on the tautomers, two types of intra-molecular hydrogen bonds are possible: O—H···N in benzenoid and N—H···O in quinoid tautomers. In the title compound the H atom is located on atom O1, thus the phenol-imine tautomer is favored over the keto-amine form, as indicated by the C2—O1, C8—N1, C1—C8 and C1—C2 bond lengths (Fig. 1 and Table 2). The O1—C2 bond length of 1.351 (2) Å indicates single-bond character, whereas the N1—C8 bond length of 1.277 (2) Å indicates a high degree of double-bond character. A similar result was observed in the X-ray crystal and computational structural study of (E)-2-[(2-chlorophenyl) iminomethyl]-4-methoxyphenol [C—O=1.357 (17) Å, C—N= 1.278 (17) Å, Özek et al., 2008.
It is known that Schiff bases may exhibit thermochromism or photochromism, depending on the planarity or non-planarity of the molecule, respectively. Therefore, one can expect photochromic properties in (I) caused by non-planarity of the molecules; the dihedral angle between ring A (C1—C6) and ring B (C9—C14) is 29.25 (8) °. The intramolecular O—H···N hydrogen bond (Table 1) results in the formation of a nearly planar six-membered ring C (O1/H1/N1/C1/C2/C8), in which it is oriented with respect to rings A and B at dihedral angles of A/C= 0.91 (1) ° and B/C= 28.91 (12) °. It is thus coplanar with the adjacent ring A. It generates an S(6) ring motif. The O1···N1 distance of 2.5962 (18) Å is comparable to those observed for analogous hydrogen bonds in three (E)-2-[(bromophenyl)iminomethyl]-4-methoxyphenols [2.603 (2) Å, 2.638 (7) Å, 2.577 (4) Å; Özek et al., 2007]. In the crystal structure, weak intermolecular C—H···O hydrogen bonds (Table 1) result in the formation of C(8) chains along the c axis (Fig. 2), which may play a role in the stabilization of the structure.