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Acta Crystallogr Sect E Struct Rep Online. 2009 July 1; 65(Pt 7): o1572.
Published online 2009 June 13. doi:  10.1107/S1600536809021278
PMCID: PMC2969358

2-[(2,4-Dimethyl­phen­yl)imino­meth­yl]-3,5-dimethoxy­phenol

Abstract

X-ray analysis reveals that the title Schiff base compound, C17H19NO3, possesses both OH and NH tautomeric character in its mol­ecular structure. The occupancies of the enol and keto tautomers are 0.62 (3) and 0.38 (3), respectively. The presence of the minor keto form could not be confirmed from the IR spectrum. The mol­ecule is approximately planar, the dihedral angle between the planes of the two aromatic rings being 6.97 (8)°. The mol­ecular structure of the major component is stabilized by an intra­molecular O—H(...)N hydrogen bond, which generates an S(6) ring motif (N—H(...)O hydrogen bond in the minor component).

Related literature

For tautomeric forms of Schiff bases, see: Becker et al. (1987 [triangle]); Seliger et al. (1990 [triangle]); Sugawara et al. (1999 [triangle]); Tezer & Karakus (2009 [triangle]). For bond-length data, see: Allen et al. (1987 [triangle]); Ogawa & Harada (2003 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-65-o1572-scheme1.jpg

Experimental

Crystal data

  • C17H19NO3
  • M r = 285.33
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-o1572-efi1.jpg
  • a = 4.7070 (2) Å
  • b = 11.283 (5) Å
  • c = 28.216 (5) Å
  • β = 97.542 (11)°
  • V = 1485.6 (7) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.09 mm−1
  • T = 296 K
  • 0.67 × 0.31 × 0.09 mm

Data collection

  • Stoe IPDS II diffractometer
  • Absorption correction: integration (X-RED32; Stoe & Cie, 2002 [triangle]) T min = 0.977, T max = 0.994
  • 13316 measured reflections
  • 2797 independent reflections
  • 1808 reflections with I > 2σ(I)
  • R int = 0.043

Refinement

  • R[F 2 > 2σ(F 2)] = 0.043
  • wR(F 2) = 0.111
  • S = 0.98
  • 2797 reflections
  • 195 parameters
  • H-atom parameters constrained
  • Δρmax = 0.09 e Å−3
  • Δρmin = −0.14 e Å−3

Data collection: X-AREA (Stoe & Cie, 2002 [triangle]); cell refinement: X-AREA; data reduction: X-RED32; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 [triangle]); software used to prepare material for publication: WinGX (Farrugia, 1999 [triangle]).

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809021278/ci2808sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809021278/ci2808Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This study was supported financially by the Research Center of Ondokuz Mayıs University (Project No. F-476). 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 No. F279 of the University Research Fund).

supplementary crystallographic information

Comment

Proton tautomerism plays an important role in many fields of chemistry and biochemistry (Sugawara et al., 1999). The study of ground state intramolecular proton (hydrogen) transfer (IPT) reactions have received increasing attention in recently aiming at the characterization of a large number of compounds in which rapid hydrogen migration occurs both in solution and in solid state. Salicilidine aniline and its derivatives are among the earliest examples of a chemical system involving IPT. A prototropic tautomeric attitude has been recognized in a number of aromatic Schiff bases (Becker et al., 1987; Seliger et al., 1990; Tezer & Karakus, 2009). O-hydroxy Schiff bases are of interest mainly due to the existence of O—H···N and N—H···O type hydrogen bonds and tautomerism between the enol-imine (OH) and keto-amine (NH) forms.

The X-ray analysis reveals that in the title compound both the enol (OH) and keto (NH) tautomers coexist with occupancies of 0.62 (3) and 0.38 (3), respectively. But we are unable to confirm the presence of minor keto form from the IR spectrum. The major enol (OH) tautomer is shown in Fig. 1. The C2—O1 [1.3312 (18) Å] bond length is intermediate between the C—O single (1.362 Å) and C═O double (1.222 Å) bonds. Similarly, the C7—N1 bond length of 1.293 (2) Å is shorter than C—N and C═N bond lengths (1.339 and 1.279 Å, respectively; Allen et al., 1987). The shortened C2—O1 bond and the slightly longer C7—N1 bond provide structural evidence for the double tautomeric forms of the title compound. Similar result was observed for N-(5-chloro-2-hydroxybenzylidene) -4-hydroxyaniline [C—O = 1.321 (2) and C—N = 1.293 (2) Å; Ogawa & Harada, 2003].

The molecule of the title compound is approximately planar, with the dihedral angle between the two aromatic rings being 6.97 (8)°. The molecular structure is stabilized by an intramolecular O1—H1A···N1 hydrogen bond (Table 1) which generates a six-membered ring, producing a S(6) ring motif. It is known that Schiff bases may exhibit thermochromism or photochromism, depending on the planarity or non-planarity of the molecule, respectively. Therefore, the title compound may exhibit thermochromic properties.

No significant π-π interactions are observed in the crystal structure.

Experimental

A solution of 2-hydroxy-4,6-dimethoxy-benzaldehyde (0.0389 g, 0.21 mmol) in ethanol (20 ml) was added to a solution of 2,4-dimethylaniline (0.0263 g, 0.21 mmol) in ethanol (20 ml). The reaction mixture was stirred for 1 h under reflux. Single crystals suitable for X-ray analysis were obtained from ethyl alcohol by slow evaporation (yield 59%; m.p.386–388 K).

Refinement

C-bound H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.96 Å and Uiso(H) = 1.2-1.5Ueq(C). The C15-methyl group was refined as idealized disordered one with two positions rotated from each other by 60°. At this stage, the hydroxyl H atom, H1A, was located in a difference map and attempts to refine it freely resulted in a very long O-H distance of 1.22 (3) Å. When the O-bound H atom was positioned geometrically a new peak at 0.97 Å from N1 was observed, indicating a disorder in the H atom i.e the presence of both OH and NH tautomers. At this stage both O and N-bound H atoms, H1A and H1B, were positioned geometrically and their occupancies were refined to 0.62 (3) and 0.38 (3), respectively. The refinement shows the enol form is the major component. The IR spectrum of the compound confirms only the presence of enol form and we are unable to confirm the minor keto form from the IR spectrum.

Figures

Fig. 1.
The molecular structure of the title compound, showing the atom-numbering scheme and 50% probability diplacement ellipsoids. Only the enol (OH) tautomer is shown. Also, only one component of the disordered C15-methyl group is shown.

Crystal data

C17H19NO3F(000) = 608
Mr = 285.33Dx = 1.276 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ybcCell parameters from 10962 reflections
a = 4.7070 (2) Åθ = 1.5–26.2°
b = 11.283 (5) ŵ = 0.09 mm1
c = 28.216 (5) ÅT = 296 K
β = 97.542 (11)°Prism, yellow
V = 1485.6 (7) Å30.67 × 0.31 × 0.09 mm
Z = 4

Data collection

Stoe IPDS II diffractometer2797 independent reflections
Radiation source: fine-focus sealed tube1808 reflections with I > 2σ(I)
plane graphiteRint = 0.043
Detector resolution: 6.67 pixels mm-1θmax = 25.6°, θmin = 1.5°
rotation method scansh = −5→5
Absorption correction: integration (X-RED32; Stoe & Cie, 2002)k = −13→13
Tmin = 0.977, Tmax = 0.994l = −34→34
13316 measured reflections

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.043Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.111H-atom parameters constrained
S = 0.98w = 1/[σ2(Fo2) + (0.0599P)2] where P = (Fo2 + 2Fc2)/3
2797 reflections(Δ/σ)max = 0.001
195 parametersΔρmax = 0.09 e Å3
0 restraintsΔρmin = −0.14 e Å3

Special details

Experimental. 240 frames, detector distance = 130 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/UeqOcc. (<1)
O1−0.1970 (3)0.07461 (10)0.06735 (5)0.0759 (4)
H1A−0.06860.08470.08960.114*0.62 (3)
O2−0.3588 (3)0.47471 (10)0.10480 (4)0.0735 (4)
O3−0.9431 (3)0.29177 (10)−0.02381 (4)0.0721 (4)
N10.1167 (3)0.18286 (12)0.13482 (5)0.0584 (4)
H1B0.07960.12070.11750.070*0.38 (3)
C1−0.2694 (3)0.27691 (13)0.08638 (6)0.0534 (4)
C2−0.3428 (4)0.17509 (14)0.05865 (6)0.0580 (4)
C3−0.5703 (4)0.17634 (14)0.02150 (6)0.0610 (5)
H3−0.61860.10850.00350.073*
C4−0.7208 (3)0.27934 (14)0.01202 (6)0.0569 (4)
C5−0.6564 (4)0.38249 (14)0.03878 (6)0.0593 (4)
H5−0.76160.45150.03170.071*
C6−0.4362 (3)0.38028 (13)0.07557 (6)0.0553 (4)
C7−0.0392 (3)0.27603 (14)0.12467 (6)0.0565 (4)
H7−0.00020.34430.14280.068*
C80.3450 (3)0.17699 (14)0.17280 (6)0.0555 (4)
C90.4693 (3)0.06605 (15)0.18298 (6)0.0590 (4)
C100.6896 (4)0.05720 (16)0.22082 (6)0.0657 (5)
H100.7713−0.01680.22790.079*
C110.7925 (4)0.15256 (17)0.24829 (6)0.0655 (5)
C120.6723 (4)0.26180 (17)0.23629 (7)0.0694 (5)
H120.74120.32830.25360.083*
C130.4512 (4)0.27460 (16)0.19910 (6)0.0661 (5)
H130.37360.34920.19180.079*
C140.3707 (4)−0.04062 (15)0.15315 (7)0.0758 (6)
H14A0.4782−0.10890.16530.114*
H14B0.4005−0.02690.12060.114*
H14C0.1706−0.05400.15460.114*
C151.0290 (4)0.1388 (2)0.28958 (7)0.0865 (6)
H15A0.99770.19300.31460.130*0.50
H15B1.21030.15550.27890.130*0.50
H15C1.02930.05900.30150.130*0.50
H15D1.16050.07870.28210.130*0.50
H15E0.94790.11620.31770.130*0.50
H15F1.12890.21270.29520.130*0.50
C16−0.5298 (4)0.57876 (15)0.09754 (7)0.0788 (6)
H16A−0.45720.63800.12040.118*
H16B−0.72420.56020.10150.118*
H16C−0.52320.60820.06580.118*
C17−1.0150 (5)0.19050 (17)−0.05323 (8)0.0852 (7)
H17A−1.17350.2093−0.07700.128*
H17B−1.06700.1261−0.03390.128*
H17C−0.85290.1679−0.06860.128*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
O10.0732 (8)0.0612 (7)0.0852 (9)0.0155 (6)−0.0198 (7)−0.0036 (7)
O20.0791 (9)0.0578 (7)0.0746 (8)0.0127 (6)−0.0235 (7)−0.0093 (6)
O30.0703 (8)0.0676 (7)0.0697 (8)0.0140 (6)−0.0237 (6)−0.0097 (6)
N10.0537 (8)0.0624 (8)0.0559 (8)0.0062 (6)−0.0046 (7)0.0033 (6)
C10.0488 (9)0.0570 (9)0.0529 (9)0.0024 (7)0.0002 (7)0.0055 (7)
C20.0541 (10)0.0562 (9)0.0613 (10)0.0076 (7)−0.0010 (8)0.0058 (8)
C30.0585 (10)0.0574 (9)0.0635 (10)0.0047 (8)−0.0058 (8)−0.0043 (8)
C40.0513 (9)0.0615 (9)0.0548 (10)0.0041 (7)−0.0048 (8)0.0020 (8)
C50.0575 (10)0.0553 (9)0.0616 (10)0.0094 (7)−0.0054 (8)0.0037 (8)
C60.0555 (10)0.0538 (8)0.0545 (9)0.0004 (7)−0.0009 (8)0.0006 (7)
C70.0534 (9)0.0598 (9)0.0549 (10)0.0010 (8)0.0009 (8)0.0021 (7)
C80.0476 (9)0.0671 (10)0.0499 (9)0.0022 (7)−0.0013 (7)0.0033 (8)
C90.0538 (10)0.0672 (10)0.0542 (10)0.0052 (8)0.0008 (8)0.0053 (8)
C100.0570 (10)0.0762 (11)0.0614 (11)0.0099 (8)−0.0018 (9)0.0105 (9)
C110.0494 (10)0.0920 (13)0.0531 (10)0.0037 (9)−0.0002 (8)0.0085 (9)
C120.0607 (11)0.0834 (12)0.0613 (11)−0.0051 (9)−0.0023 (9)−0.0070 (9)
C130.0595 (11)0.0696 (10)0.0661 (11)0.0056 (8)−0.0034 (9)−0.0001 (9)
C140.0810 (13)0.0660 (11)0.0750 (12)0.0091 (9)−0.0097 (10)0.0030 (9)
C150.0623 (12)0.1271 (17)0.0645 (12)−0.0006 (11)−0.0125 (10)0.0102 (12)
C160.0879 (14)0.0586 (10)0.0823 (13)0.0180 (9)−0.0175 (11)−0.0103 (9)
C170.0864 (14)0.0770 (12)0.0816 (13)0.0157 (10)−0.0293 (11)−0.0214 (10)

Geometric parameters (Å, °)

O1—C21.3312 (18)C10—C111.376 (3)
O1—H1A0.82C10—H100.93
O2—C61.3673 (19)C11—C121.380 (3)
O2—C161.4229 (19)C11—C151.510 (2)
O3—C41.3634 (18)C12—C131.385 (2)
O3—C171.427 (2)C12—H120.93
N1—C71.293 (2)C13—H130.93
N1—C81.4159 (19)C14—H14A0.96
N1—H1B0.86C14—H14B0.96
C1—C21.407 (2)C14—H14C0.96
C1—C61.416 (2)C15—H15A0.96
C1—C71.426 (2)C15—H15B0.96
C2—C31.397 (2)C15—H15C0.96
C3—C41.369 (2)C15—H15D0.96
C3—H30.93C15—H15E0.96
C4—C51.399 (2)C15—H15F0.96
C5—C61.367 (2)C16—H16A0.96
C5—H50.93C16—H16B0.96
C7—H70.93C16—H16C0.96
C8—C131.384 (2)C17—H17A0.96
C8—C91.396 (2)C17—H17B0.96
C9—C101.391 (2)C17—H17C0.96
C9—C141.507 (2)
C2—O1—H1A109.5C8—C13—C12120.38 (17)
C6—O2—C16117.08 (12)C8—C13—H13119.8
C4—O3—C17116.70 (13)C12—C13—H13119.8
C7—N1—C8123.93 (15)C9—C14—H14A109.5
C7—N1—H1B118.0C9—C14—H14B109.5
C8—N1—H1B118.0H14A—C14—H14B109.5
C2—C1—C6117.64 (14)C9—C14—H14C109.5
C2—C1—C7121.47 (14)H14A—C14—H14C109.5
C6—C1—C7120.88 (14)H14B—C14—H14C109.5
O1—C2—C3118.22 (14)C11—C15—H15A109.5
O1—C2—C1120.65 (14)C11—C15—H15B109.5
C3—C2—C1121.13 (14)H15A—C15—H15B109.5
C4—C3—C2118.77 (15)C11—C15—H15C109.5
C4—C3—H3120.6H15A—C15—H15C109.5
C2—C3—H3120.6H15B—C15—H15C109.5
O3—C4—C3124.01 (14)C11—C15—H15D109.5
O3—C4—C5113.93 (13)H15A—C15—H15D141.1
C3—C4—C5122.06 (14)H15B—C15—H15D56.3
C6—C5—C4118.92 (14)H15C—C15—H15D56.3
C6—C5—H5120.5C11—C15—H15E109.5
C4—C5—H5120.5H15A—C15—H15E56.3
O2—C6—C5124.00 (14)H15B—C15—H15E141.1
O2—C6—C1114.55 (13)H15C—C15—H15E56.3
C5—C6—C1121.46 (15)H15D—C15—H15E109.5
N1—C7—C1121.77 (15)C11—C15—H15F109.5
N1—C7—H7119.1H15A—C15—H15F56.3
C1—C7—H7119.1H15B—C15—H15F56.3
C13—C8—C9119.42 (15)H15C—C15—H15F141.1
C13—C8—N1123.59 (15)H15D—C15—H15F109.5
C9—C8—N1116.99 (14)H15E—C15—H15F109.5
C10—C9—C8118.20 (16)O2—C16—H16A109.5
C10—C9—C14121.02 (15)O2—C16—H16B109.5
C8—C9—C14120.76 (14)H16A—C16—H16B109.5
C11—C10—C9123.23 (17)O2—C16—H16C109.5
C11—C10—H10118.4H16A—C16—H16C109.5
C9—C10—H10118.4H16B—C16—H16C109.5
C10—C11—C12117.21 (16)O3—C17—H17A109.5
C10—C11—C15121.56 (18)O3—C17—H17B109.5
C12—C11—C15121.23 (18)H17A—C17—H17B109.5
C11—C12—C13121.49 (17)O3—C17—H17C109.5
C11—C12—H12119.3H17A—C17—H17C109.5
C13—C12—H12119.3H17B—C17—H17C109.5
C6—C1—C2—O1−179.15 (16)C7—C1—C6—C5179.61 (16)
C7—C1—C2—O1−0.4 (3)C8—N1—C7—C1−179.15 (15)
C6—C1—C2—C30.6 (3)C2—C1—C7—N11.8 (3)
C7—C1—C2—C3179.39 (17)C6—C1—C7—N1−179.44 (15)
O1—C2—C3—C4−179.62 (16)C7—N1—C8—C13−9.1 (3)
C1—C2—C3—C40.6 (3)C7—N1—C8—C9172.11 (16)
C17—O3—C4—C3−1.3 (3)C13—C8—C9—C102.6 (3)
C17—O3—C4—C5178.46 (17)N1—C8—C9—C10−178.54 (15)
C2—C3—C4—O3178.77 (17)C13—C8—C9—C14−176.31 (17)
C2—C3—C4—C5−0.9 (3)N1—C8—C9—C142.6 (2)
O3—C4—C5—C6−179.76 (16)C8—C9—C10—C11−0.7 (3)
C3—C4—C5—C60.0 (3)C14—C9—C10—C11178.17 (18)
C16—O2—C6—C53.4 (3)C9—C10—C11—C12−1.5 (3)
C16—O2—C6—C1−176.22 (17)C9—C10—C11—C15179.01 (18)
C4—C5—C6—O2−178.32 (16)C10—C11—C12—C131.9 (3)
C4—C5—C6—C11.3 (3)C15—C11—C12—C13−178.59 (18)
C2—C1—C6—O2178.09 (15)C9—C8—C13—C12−2.2 (3)
C7—C1—C6—O2−0.7 (2)N1—C8—C13—C12178.98 (17)
C2—C1—C6—C5−1.6 (3)C11—C12—C13—C8−0.1 (3)

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
O1—H1A···N10.821.82 (1)2.561 (2)149
N1—H1B···O10.861.86 (1)2.561 (2)137 (1)

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CI2808).

References

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  • Farrugia, L. J. (1999). J. Appl. Cryst.32, 837–838.
  • Ogawa, K. & Harada, J. (2003). J. Mol. Struct.647, 211–216.
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